Difference between revisions of "Brakes"

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You can have all the power in the world, but at some point you're going to want to slow your [[E30]] down. When it's time for some middle-pedal action, get to know what your [[Brakes|brakes]] up are up to.
  
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__TOC__
  
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== Basic checks: ==
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=Overview=
  
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All E30s are fitted with a hydraulic braking system. When the [[Brakes#Brake_Pedal|pedal]] is pressed, fluid is pressurised by the [[Brakes#Master_Cylinder|Master cylinder]] to send [[Brakes#Brake_Fluid|fluid]] to each wheel. To help, extra pressure is generated by the [[Brakes#Brake_Servo|servo]], driven by the engine. This pressurised fluid powers the braking system, which on all E30s comprises of front [[Brakes#Discs|discs]] and either rear discs or [[Brakes#Drums|drums]]. A the front, the brake fluid will pressurise two [[Brakes#Calipers|calipers]], which will squeeze [[Brakes#Pads|pads]] against the discs to convert the kinetic energy of the rotating disc into heat. To a smaller degree, [[Brakes#Cylinders|cylinders]] on the rear will press [[Brakes#Shoes|shoes]] against the inside face of the drums to achieve the same effect.
  
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First off, ensure the callipers are in full working order (no sticking pistons, seals etc) and the brakes hoses are in good condition before embarking on any upgrade. Also check the servo is working properly if fitted (a duff servo normally gives you a hard pedal with a lack of braking force) and that the master cylinder seals are good (leaking seals give you a soft pedal, often slowly "sinking" if held under pressure).
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When you want the car to stay still, a cable-operated [[Brakes#Handbrake|handbrake]] will lock the rear shoes in place. On cars fitted with rear discs, small handbrake shoes work on the inside of the rear disc.
  
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Keeping all of the components fresh and leak free will help massively in preventing car/tree interactions.
  
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=Components=
  
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== What can be improved? ==
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==Brake Pedal==
  
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The brake pedal forms part of the pedal box, and it may surprise you to know that it is how the brakes are activated by the driver. It is connected to the [[Brakes#Master_Cylinder|master cylinder]] through a pull rod, which can be adjusted to control pedal height. There's a small rubber buffer on the lowest part of the bracket that holds the [[Brakes#Brake_Light_Switch|brake light switch]], and the rod should be shortened until the arm of the pedal all but touches this buffer.
  
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There are a lot of closely interrelated aspects surrounding brake system operation, many areas can be improved but at the expense of another area. This makes everything a compromise, here are the aspects with their effects on performance etc:
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To adjust the brake pedal, slacken off the lock nuts and turn the pull rod using a 7mm open-ended spanner on the flats near the [[Drivetrain#Clutch|clutch]] pedal to adjust, until the brake pedal only has a small bit of upwards free movement to its stop. One end of this rod has a reverse thread, so turning it changes its length.
  
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Be careful though. If you over-tighten things, so that the pedal is touching the buffer and moving the [[Brakes#Master_Cylinder|master cylinder]] push rod, the brakes are likely to lock on.
  
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'''Brake "power"'''
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===Brake Light Switch===
  
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ie torque at the wheel for a given brake fluid pressure. This can be improved in several ways:
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The brake light switch is mounted to a frame just above the pedal arm, and is held in place with two small plastic tabs on its sides. It goes directly to the main loom, where it feeds the rear lights, and the [[Instruments#Check_Panel|Check Panel]] and [[Cruise_Control|Cruise Control]] if fitted. For cars fitted with a Check Panel, it is normal for the brake fault light to glow the moment the ignition is turned on; it will turn off the moment the brake pedal is pressed.  
  
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1 - Larger discs, this in effect increases the leverage that acts on the wheel. Downsides are increased unsprung mass (and rotational mass due to the larger diameter), a slight increase in cost if it's a re-drilled one-piece disc or a larger increase in cost if it's alloy bells and rotors.
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==Brake Servo==
  
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2 - Higher coefficient of friction in the pad material. Downsides are that in most performance pads they work better when warm/hot, and full race pads hardly work at all when cold, plus increased cost.
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The brake servo powers the [[Brakes#Master_Cylinder|master cylinder]], making it easier on your braking foot. However, it does not improve braking performance; it simply takes the weight off your leg by replacing muscles with vacuum pressure.
  
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3 - Larger pistons in the caliper (and/or smaller master cylinder piston/s). This increases the mechanical advantage that the system gives your foot over the force applied to the back of the pads, but like all forms of increased leverage the longer the "lever" the longer the travel needed at the input end. In the case of brakes, the added clamping force at the pad is offset by a longer travel / softer pedal.
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It gets this extra pressure via hoses from the [[Intake#Rubber_Boot|rubber boot]] on the engine intake system. Earlier cars used a very complex arrangement of hoses to supply pressure, for reasons unknown, while later systems were significantly simpler, using just one pipe from the [[Intake#Throttle_Body|throttle body]] to the servo.  
  
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When changing your engine or replacing your rubber boot, it is very common to find that you don't have the right number of holes to correctly connect your brake servo. Over the years, BMW tried all sorts of plumbing solutions to provide vacuum to the brake servo, and this resulted in a large variety of rubber boots on the market. If you find that your rubber boot doesn't have the right number of holes, simply connect all the other hoses to the brake servo in the most direct way possible, and plug any other holes.
  
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'''Unsprung mass,'''
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To check the condition of your servo, pump the brake pedal a few times with the engine off to get rid of any vacuum in the the servo. Then press your foot on the brake pedal and hold pressure on it as you start the car. You should feel the pedal drop a bit as the vacuum builds. If it does not you may have a vacuum leak or other servo problem.
  
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This is the effect of the mass of the brakes fitted to the strut, where they are not properly "sprung and damped" by the suspension like the chassis is. The lighter a brake system is, the faster and more controlled the suspension action can be, giving the car more grip. The downsides to lighter brake discs, is that they heat up faster due to the lower "thermal mass", but lighter calipers, pads, alloy bells and mounting brackets all give you "free grip".
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Servos are interchangeable across the entire E30 range. For those attempting an [[M50]] or [[M52]] engine swap, a Renault Clio (2000 or later) brake servo is a smaller alternative than the standard unit, and bolts straight up. It only requires a spacer at the end of the pull rod to remove pedal slack. This is a much better option than the old Mk 1 Gold servo.
  
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===Intake Valve===
  
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'''Rotational mass'''
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Because the brake servo receives air pressure from the [[Intake]], it important for that pressure not to be lost. For that reason, a one-way valve is fitted in the hoses between the [[Intake#Rubber_Boot|rubber boot]] and the brake servo. Occasionally this valve can fail, leading to loss of braking force.
  
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The lighter and smaller the brake disc (and wheel/tyre/hub etc) the less energy is needed to spin it faster or slow it down. So a lighter and smaller brake disc will give the car better acceleration, economy and braking (if the brakes magically still worked just the same!). The downsides are reduced brake power, reduced cooling from the smaller disc vents and reduced thermal mass.
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==Master Cylinder==
  
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To transfer pedal power into fluid pressure, your car is fitted with a Master Cylinder. Imagine it like a big nurse's syringe, but with four holes on it instead of one. As you press the pedal, fluid is compressed through these four holes to each wheel in turn.
  
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'''Fade (pad) resistance'''
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The standard E30 Master cylinder is a 19mm unit, and is the same across all facelift cars. There is no difference between [[Brakes#ABS|ABS]] and non-ABS cars either; cars fitted with ABS simply block up the rear two ports on the master cylinder.
  
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This is the amount of heat the brake pads can withstand before they overheat into "brake fade", this feels like you have a hard pedal but no brake power (similar to a failed servo). In the olden days pads used to "gas", where the glue in the material boiled and producing a thin layer of high pressure gas that lifted the pad off the disc using the same principles as a hovercraft uses! This lead to people drilling (and grooving) their discs to release this gas. Modern brake materials no longer gas in anything like the same way, so grilled discs are of FAR less use than they used to, and given that they can crack the main reason people buy them is for the "look". Grooved discs DO still have a place as they scrub at the face of the pads, and with many race pads they are needed to stop the pad surface "glazing".
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If the pedal sinks slowly to the floor under constant / light pressure then you have a leak, normally this is an internal master cylinder seal.  
  
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===Reservoir===
  
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'''Fade (fluid) resistance'''
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The reservoir that holds the brake fluid sits on top of the master cylinder. It is a simple container, and simply pushes into the top of the master cylinder; it does not have any screws or bolts holding it in place. It also houses the Brake Fluid Level Sensor, which is the first place to check if your brake warning light glows on the [[Instruments#Dash_Cluster|dash cluster]].
  
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This is the amount of heat the brakes can withstand without the fluid boiling, when the fluid boils the bubbles created are easily squashed by the pressure created when the pedal is pressed, making the pedal sink straight to the floor and allying almost no pressure to the pads at all! This is probably the most dangerous form of brake problem and for the few seconds it happens the effect is as ba as a burst brake line. Fluid boiling can be reduced by:
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Leaks from the Reservoir are usually caused by a perished rubber seal between the reservoir and the cylinder. To fix, simply pull the reservoir up firmly, replace the seal and relocate the reservoir.
  
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1 - Running a fluid with a higher boiling point.
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===Pressure Valve===
  
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2 - Changing the fluid regularly as water is absorbed by most brake fluids, and of course only needs 100 degrees C to boil. Also once brake fluid HAS boiled it's resistance to boiling is actually reduced, and next time it will boil at a LOWER temperature!
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Underneath the Master Cylinder is a pressure valve, for the rear brakes. Its purpose is to ensure that the rear brakes don't receive as much pressure as the fronts, because this will cause the rears to lock up which is never fun on a RWD car. Well it is, but you get the point.
  
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3 - Using cooling air from the brake duct to cool the caliper.
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The Pressure Valve was offered in two flavours; an enormous thing as big as the Master Cylinder for earlier cars, and a small metal block for later cars. These are entirely interchangeable, although they very rarely need replacing.
  
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4 - Using cooling air from the brake duct to cool a brake fluid radiator.
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==Brake Fluid==
  
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5 - Running a brake fluid recirculating valve. This clever gadget cycles the fluid into the caliper then back out and up into the main fluid reservoir, this keeps the caliper cooler and stops a stagnant volume of fluid from sitting in the caliper and getting very hot.
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''Main article: [[Brake_Fluid|Brake Fluid]]''
  
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The fluid that pulses through your braking system is the most crucial component. Just like oil for the engine, fluid needs to be [[Brakes#Replacing_Fluid|changed at regular intervals]] to keep the brakes working as they should. If you don't, moisture creeps into the system, which can cause pressure problems as well as internal corrosion.
  
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'''Heat reduction'''
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DOT 4 braking fluid should be used, although DOT 5.1 non-silicon is an acceptable alternative. It is essential to use non-silicon fluids as it can cause failure of the rubber seals in the [[Brakes#Calipers|calipers]]. Learn more about .
  
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This is mainly about keeping the disc cool to stop it "warping" and keep the pads cooler so they can operate properly. You can reduce disc temperatures by:
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==Brake Lines==
  
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1 - Having a larger disc with bigger, more efficient vents and larger area to be cooled, the downside is added unsprung/rotational mass (although mass helps in another way, next....).
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Steel brake lines run from the [[Brakes#Master_Cylinder|master cylinder]] to each wheel in turn. They are clipped to the body of the vehicle every 300mm (approx.) and use 10mm fittings.
  
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2 - Having a heavier disc, this provides more "thermal mass". Thermal mass works because it takes twice as much energy to heat twice as much mass to a given temperature, so if you double the mass while keeping the energy input constant you HALVE the temperature (before cooling efficiency etc starts to come into play). The downside is added unsprung/rotational mass.
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Over time, these steel lines will obviously rust due to all the mud at salt thrown underneath the car. and can cause lost of braking power at the wheel end or, if they burst, total brake failure caused by loss of system pressure. If the MOT man tells you to replace your brake pipes, do what he says.
  
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While replacements are still available from BMW, it can be a lot less of a headache to make your own pipes from cunifer, and bend them yourself to suit. Cunifer doesn't rust, so well-made pipes should last the lifetime of the vehicle.
  
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'''Disc "warping" resistance'''
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==Brake Hoses==
  
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It should be noted that brake discs juddering through the pedal are not "warped" in the way many people think, in most cases it's because road pads (which are abrasive) have been overheated and a high-spot has formed. This high spot gets VERY hot and into a changes into a different and much harder form of iron. Of course the new hard area is more resistant to the pad's abrasion and so as the material around it is worn away it becomes higher, which makes it hotter, and therefore even harder....and so on. The discs DO warp, but only when you press the pedal and this one high spot gets much hotter, rapidly expanding and warping the disc. The things people miss are that (1) the disc returns to a mostly non-warped state as soon as you back off the brakes or take the disc off the car for inspection, and (2) machining the disc won't fix it as there is still a hard spot in the iron waiting to start the whole process again once the abrasion or use continues! Upgrade pads often work by "smearing" their own pad material onto the disc rather than abrading the disc, thereby dodging the high-spot vicious cycle.
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Flexible brake hoses connect the brake components to the brake lines, allowing the [Wheels|wheel]] a degree of [[Suspension|travel]] as well as reducing vibrations through the system.
  
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While the brake hoses are screwed together using standard fittings, they are subjected to such harsh road conditions that it's almost impossible to remove them without damaging them, even with the correct tools. For the sake of safety, it is best to consider brake hoses disposable items.
  
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'''Resistance to high temperatures by all components in a performance/race application'''
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Brake hoses don't have to split to cause problems to the system. Over time the rubber they are made of can weaken and relax, allowing them to balloon up under braking pressure. This will stop the brake on that wheel from working properly, so always check the condition of the hoses first when looking for brake problems.
  
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If you assume that the brake system will be used and a hard and sustained way (trackdays etc) then the components ARE going to get very hot no matter what cooling you use, but there are ways to allow them to survive the temperatures and work very effectively for a sustained period.
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==Calipers==
  
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- External piston dust seals on performance calipers often burn off, but they can be omitted without causing any problems in most cases.
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All E30s were fitted with front disc brakes, which employ a caliper to squeeze two [[Brakes#Pads|pads]] to each side of a metal [[Brakes#Discs|discs]]. This resulting friction converts the discs spinning force into heat, slowing the car down. The caliper is mounted to a carrier, which allows the caliper to "float" over the disc.
  
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- Brake discs get very hot in the area that's in contact with the pads and expend with huge force. In a one-piece disc this makes the disc form cone-shape as the vented "rotor" part expands but the "bell" part stays cooler and unchanged, in (very rare) extreme cases the vented part can crack right off the bell! To reduce these forces there are two options, (1) fit an iron rotor to an aluminium bell (aluminium expends faster with temperature than iron, so the cooler bell partly "keeps up" with the hotter rotor as it expands) and (2) fitting a "radially floating rotor (there are radial slots in the rotor or the bell with sliding "bobbins" in them, this allows the rotor to expand totally freely, with no force applied to the bell)! Floating rotors are very expensive though and are almost exclusively for race-cars only - although BMW have recently used the principle on the M3, the discs have aluminium bells with radial spoke-like pegs, and the cast-iron rotor "floats" on these pegs! Also large light-weight rotors rely less on the effects of thermal mass, and more on effective cooling vents to cool the brakes on each straight section of track.
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Two types of '''FRONT''' calipers were fitted. [[M10]]- and [[M40]]-engined cars were fitted with smaller calipers that worked on solid discs, while the more powerful [[M20]]- and [[M42]]-engined cars were capable of accepting vented discs, and therefore had wider calipers.
  
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- Race pads will continue to work happily way after normal pads would have totally failed, and often get better the more abuse they get, and race brake fluid can withstand the continued high temperatures.
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Most calipers were made by ATE, although some parts were sourced by Girling and it is impossible to know what may have been fitted to any particular car without looking. The part number should be stamped on the curved face on the back of the calipers. However, the make of caliper does not affect the purchasing of pads. However, it is important if you are buying parts to rebuild your calipers.
  
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- Brake ducts are very handy as the high speeds on the straight pump much more cooling air into the brakes than on a road car.
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It is possible to fit the wider calipers and vented discs to all E30s. Parts sourced from the more powerful E30s will bolt straight on. If you are interested in much more powerful braking systems, learn more about [[Brake_Upgrades|upgrading the brakes]].
  
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== E30 brake upgrade options in stages (increasing in performance and price). ==
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The '''REAR''' calipers, as fitted to all [[M20]]-engined cars, as well as all [[Touring]]s and [[Cabriolet]]s, are fully interchangeable across all vehicles although Touring calipers have bigger pistons. If your car has [[Brakes#Drums|drums]] at the back, it is possible to convert to discs using bolt-on components. Learn more about [[Rear_Disk_Brake_conversion|converting to rear discs]].
  
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To rebuild your rear calipers, you will need two rebuild kits ('''34211153194''') which contain a piston seal, dust seal and a circlip.
  
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First would be upgrading the pads as you get some easy extra torque and fade resistance (EBC Red, Mintex M1144/1155, Ferodo DS2500 or similar pads for fast road/light trackdays or EBC Yellow/Blue or similar for more serious track use) - of course all the OEM components need to be checked over at the this stage, including the cooling ducts. Fit fresh standard brake fluid and new standard discs (worn discs have less thermal mass and won't bed in properly with new pads). There is NO NEED to get drilled and/or grooved or funny coloured discs, unless you like the look...
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==Discs==
  
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Next would be increasing the resistance to the extra heat and pressure the pads can create by fitting stainless braided lines (like Earls/Goodrich etc) and upgrading the existing brake fluid (like ATE Superblue, or Castrol SRF for a road/trackday oriented car).
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Two different discs were fitted to the front of E30s; solid discs for the smaller engines, and wider, vented discs for the more powerful versions. These discs are matched to the [[Brakes#Calipers|calipers]]; a solid disc should not be fitted to a [[325i]] because it will cause excessive piston travel and ultimately brake failure, while a vented disc will not fit to a standard [[318i]] because it simply won't get inside the caliper.
  
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There is no benefit to using drilled or grooved discs on an E30, and it is heavily recommended that you do not. Drilled discs in particular are structurally weakened by the drilling, which leads to cracks and ultimately brake failure. The standard discs fitted to E30s are more than sufficient, even for the common engine swaps of [[M30]] and [[M50]] engines.
  
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Next we move up to larger diameter discs, here are the approximate sizes possible in each wheel size:
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Learn more about [[Brakes#Replacing_Pads_and_Discs|replacing your discs]].
  
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14" - Very little room, 255mm normally (275mm in some motorsport allys).
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==Pads==
  
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15" - 280mm (300mm in some motorsport alloys). There may be a new 290-300mm 4-pot kit available next year specifically for the 15" BBS...
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The pads are made of a friction material which rubs against the discs when the brakes are pressed. Over time, this friction material will wear down, leaving you with a flat metal pad grinding and gouging the disc surface. It is very important that you change your discs BEFORE you get to this point, as it not only ruins the discs but also leads to total brake failure.  
  
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16" - 300mm (320mm in some motorsport alloys)
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All front pads are interchangeable on E30s, although some simple upgraded pads are available. Textar and Pagid pads are recommended alternatives.
  
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17" - 325mm (345mm in some motorsport alloys)
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Check the condition of the discs before you change the pads. E30 discs only last the life of two or three sets of pads.
  
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Learn more about [[Brakes#Replacing_Pads_and_Discs|replacing your pads]].
  
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Ready made upgrades includes lightweight 4-pot kits and cheaper but heavier sliding caliper kits where the buyer sources second-hand calipers:
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===Pad Wear Sensor===
  
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- The 300mm.de kit, this uses a 312mm re-drilled disc and brackets to suit a BMW sliding caliper.
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Only one pad of the four at the front (and the same at the back if you have rear discs) is fitted with a wear sensor. Pads don't wear completeley evenly, so to be on the safe side, the light usually comes on when there are several thousand miles of wear left in the pads.  
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However, you should have a look at the pads to check that none are nearly down to the metal. There is also [[Instruments#Brake_Pad_Light_Flickering|a well-known fault]] in the [[Instruments#Brake_Lights|instrument cluster]] that puts the pad wear light on intermittently.
  
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- The WMS 280mm 4-pot kit, which is confirmed as fitting the 15" BBS and has custom 1.25" E30-specific pistons.
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==Drums==
  
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- The Wilwood 280mm and 310mm 4-pot kits which have 1.38" pistons.
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The back end of the small-engined saloons were fitted with drum brakes. Unlike [[Brakes#Calipers|calipers]], the braking force is applied to the inside face of the drum, whereby a brake [[Brakes#Cylinders|cylinder]] pushes out two curved [[Brakes#Shoes|shoes]]. These shoes rub against the drum to create friction, and therefore heat.
  
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- Other kits from mfrs including AP Racing, Brembo, Alcon, and Hi Spec.
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Although the rear wheels are driven, they receive a let less braking force than the front wheels due to the [[Brakes#Pressure_Valve|pressure valve]], and therefore a less sophisticated braking system is needed.
  
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However, drums are particularly irksome when it comes to servicing and repairing, with many E30 owners choose to convert to rear discs. Parts availability, and ease of servicing in the future, make this a very popular modification. Learn more about [[Rear_Disk_Brake_conversion|converting to rear discs]].
  
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==Cylinders==
  
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Another option is to scour eBay and breakers yards for crashed cars that already have 4 pots or compatible sliding calipers fitted and make your own brackets. If you are prepared to look around to find parts,and are happy to fabricate calliper brackets, then a budget big brake set-up can be achieved for around 40% less than the equivalent off the shelf items.DIY kits have included:
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To make the [[Brakes#Shoes|shoes]] press against the drum, a cylinder is fitted. The cylinder is little more than two rods, pushed out and in by the changing fluid pressure in the system. When the brake pedal is pressed, the rods in the cylinder extend, forcing the face of the shoes against the drum.  
  
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- 302mm disks with 4 pot callipers can be made to fit under 16" wheels - Baddave's current setup which apparently works rather well.
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Despite the simplicity, the relative size of cylinders makes them fragile, and for peace of mind they should be replaced at the same time as the shoes.
  
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- <<please update me>>
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==Shoes==
  
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<<Please update me with M/C and Servo options for firming up the stock set-up>>
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Shoes in drum brakes come in two flavours. For rear drum brakes, a large pair of shoes is required. These are simple metal curves with a friction pad on the outside face, designed to make maximum contact with the drum.
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E30 M3 master cylinder with stock servo
 
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E32 750i Master cylinder with stock servo (for those who have fitted calipers with a substantial increase in piston area)
 
  
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'''Cars with E30 compatible discs'''
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The shoes are joined at their base with a high-tension coil spring. When detaching this spring, only stretch it by hooking a piece of fine but strong wire around the ends and pulling on the wire, otherwise you are likely to lose the skin off your fingertips.
  
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*Audi TT with some drilling ??
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For cars with rear [[Brakes#Discs|discs]], a smaller pair of shoes is fitted to the inside 'bell' of the disc. These are for the [[Brakes#Handbrake|handbrake]], and therefore do not need to be so large.
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*Chrysler Voyager 302x28mm with redrilled holes(disk offset is near perfect)
 
  
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'''E30 compatible Master Cylinders '''
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==Handbrake==
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''Main article: [[Handbrake]]''
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[[Image:28052007259.jpg|thumb|right|Rear disc handbrake setup]]
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The handbrake is a cable-operated mechanism separate from the hydraulic brake setup. On all cars, the handbrake controls [[Brakes#Shoes|shoes]] on the rear wheel, regardless of whether the car has [[Brakes#Discs|discs]] or [[Brakes#Drums|drums]].
  
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<<Please update me>>
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The handbrake lever is bolted to the [[Drivetrain|transmission]] tunnel inside the car, and is covered with a gaiter. If you remove this gaitor, you will see that the arm sits on two small metal contacts which power the [[Instruments|handbrake light]], which should light when the handbrake is lifted.
  
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*Bmw E30M3
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In the middle of the lever are two threaded rods with nuts. These rods attach to two cables that run from the handbrake lever to each rear wheel. These cables run through protective sleeves to the rear wheels, where they will pull on the handbrake mechanism; a simple mechanical arm that pulls the [[Brakes#Shoes|shoes]] outwards to rub against the inside edge of the [[Brakes#Discs|disc]] or [[Brakes#Drums|drum]]. These cables are specific to disc and drum brakes, and if they need to be replaced, they are a massive headache due to their construction. Brute force and a blowtorch is often the only way to get old cables off the car.
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*Bmw E32 750i
 
  
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With drum brakes, the handbrake is self-adjusting, and any handbrake issues are usually cable-related or rusty mechanisms. With rear discs, the bottom of the shoes are pushed by the handbrake and the top are pushed by a static adjuster. If you only adjust the handbrake at the lever then you don't get full shoe contact and you'll get odd wear and a reduced efficiency handbrake. Learn more about [[Brakes#Adjusting_Handbrake|adjusting the handbrake]].
  
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'''Cars with 4pot calipers'''
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[[Z3]] handbrake shoes from a 6-cylinder model fit rear-disc E30 models. Use the Z3 shoes, pins, retaining springs, pull off springs and adjuster, but retain the E30 expander. This will result in a much firmer, more solid handbrake.
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*Aston Martin(various)-DB7
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==ABS==
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*Alfa Romeo GTV/166
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*Audi Possibly RS2,S8,RS8
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''Main article: [[ABS]]''
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*BMW E38 730i, 735i
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*BMW E34 3.8L M5(very last ones)
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The Anti-Lock Braking System fitted to some E30s is a relatively simple system designed to, well, stop the wheels from locking up. To do this, the pressure to the brakes is pulsed rather then constantly applied, applying a hard then soft force to allow the wheel to still rotate. While this may seem daft in straight-line braking, for cornering it allows the front wheels to still turn the car away from its current direction, so that you don't slide straight into a tree in a cloud of smoke.
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*BMW E31 840i,850i,850csi
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*Citroen C8 possibly (going by pad shape)
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This pulsing pressure is applied through an ABS pump, which accepts fluid straight from the [[Brakes#Master_Cylinder|Master Cylinder]] and sends it onwards to each wheel in turn. Because of this, fewer fluid pipes are needed so for ABS vehicles, the rear ports of the Master Cylinder are blanked off.
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*Ferrari (all newer models)
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*Fiat Coupe
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On each wheel an ABS sensor is fitted, which tracks the rotation speed of each wheel. A sensor is also fitted in the pump to measure incoming braking pressure. When the brake pedal is applied, the ABS ECU will immediately read from each sensor, and if the pressure is hight enough, the ABS pump will pulse. This often feels strange the first time its used, and many new E30 owners spend subsequent wasted hours looking for braking faults. Don't worry, you just have ABS.
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*Fiat Ulysee possibly(going by pad shape)
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*Ford Focus RS
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For track and race preparation, ABS can be easily removed with very little work. The Master Cylinder does not need to be replaced, but brake lines need to be attached to the rear ports on the cylinder to feed the appropriate wheels.
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*Ford Puma(racing) fitted with Alcon 4pots as standard
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*Ford Sierra RS Cosworth 3dr
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If you're having issues, learn more about [[ABS_Problems|ABS Problems]].
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*Jaguar S type R
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*Lamborghini(all newer models)
+
=Servicing=
−
*Lancia Delta(integrale)
+
 
−
*Lancia Phedra
+
No brakes = no car. But you don't want to get into a position where you don't have any brakes, so preventative maintenance '''MUST''' be done regularly. The following parts should be inspected and replaced regularly
−
*Lotus Carlton (AP group C spec)
+
 
−
*Range Rover(newer ones have Brembo's)
+
==Bleeding==
−
*Mazda RX-7
+
 
−
*Mercedes ( most of the higher spec AMG variants)
+
Bleeding is the process of expelling [[Brakes#Air|air]] from the system, and is necessary if you've disconnected any of the hydraulic components.
−
*Mitsibishi 3000GT
+
 
−
*Mitsibishi Lancer ( from Evo 4 onwards iirc)
+
The process is relatively simple, but requires two people. If you have a one-man bleeding kit, follow the instructions provided.
−
*Nissan 300ZX
+
 
−
*Nissan Skyline (R33GTR/R34GTR)
+
Bleeding is done by releasing a special screw on each brake, called a bleed screw. The brake pedal is then pressed to push air out, and the screw retightened. In practice, several pedal pumps are required on each wheel, requiring co-operation between the unscrewer and the pedal-pusher. If the pedal is released while the screw is undone, air will be sucked back into the system and you will have to start all over again, so choose an assistant you can both trust and punch when things go wrong.
−
*Nissan 350Z
+
 
−
*Peugeot 607(possibly)
+
To start, locate the bleed screw on each [[Brakes#Calipers|caliper]] or [[Brakes#Cylinders|cylinder]] and soak it in a good penetrating oil (like WD40) repeatedly for up to a week before attempting to bleed. Bleed screws are notoriously fragile, and if you break one they are becoming increasingly expensive to replace from BMW.
−
*Peugeot 807(possibly)
+
 
−
*Peugeot 406 Coupe
+
# When ready, crack off the bleed screw with a proper brake spanner to reduce the risk of rounding off the bolts.
−
*Porsche 911/928/944/959/968/Boxster/Cayenne/Cayman
+
# Unscrew one quarter turn
−
*Renault Clio Sport(mid engined version)
+
# Have assistant press AND HOLD the brake pedal
−
*MG MGF
+
# Retighten bleed screw
−
*Seat Cupra R (Ibiza,Leon)
+
# Have assistant release brake pedal
−
*Subaru Impeza STI
+
# Repeat steps 2-5 until fluid seeps from the bleed screw. At this point, retighten the screw fully and move to the next wheel.
−
*Toyota Hilux
+
 
−
*Toyota Celica GT4
+
When you have bled each wheel in turn, check the pedal for sponginess. If the pedal is still too soft, re-bleed all four wheels again in the same sequence. If the pedal still feels soft, learn more about [[Brakes#Soft_Brakes|soft brakes]].
−
*Toyota Supra
+
 
−
*TVR ( certain newer models)
+
==Replacing Pads and Discs==
 +
 
 +
When working on brakes, ensure that any wheels touching the ground are chocked, so that they cannot move.
 +
 
 +
For '''FRONT''' discs:
 +
The first step is to lever the pads and the caliper away from the disc. do this by inserting a screwdriver behind the pad (there should be a small lip on the pad you can get leverage on) and pulling the s/driver towards you.
 +
 
 +
Then loosen the caliper bolts. I recommend using a hex socket as opposed to an allen wrench. The allen bolts are 7mm and are in there pretty tight. They loosen fairly easliy with a ratchet. Once the bolts are all the way loose, simply pull the caliper off the rotor. Don't let it hang from the brake line though; support it on a jackstand, or suspend it with stiff wire from the suspension spring. Extract the pads.
 +
 
 +
Now remove the small 6mm hex screw in the face of the disc, and give the disc an allmighty wallop with a hammer to get it off the hub.
 +
 
 +
When you put the new stuff on, squeeze the piston on the caliper back in with some large swan leg pliers, clean all the dirt off the caliper carrier with a wire brush, and apply plenty of copper grease to the back of the pads (not the face that goes on the disc!)  
 +
 
 +
Installation is opposite of removal. Remember to pump the pedal before driving away, to return the caliper piston to its proper location.
 +
 
 +
For '''REAR''' discs:
 +
 
 +
First you need to take out the pre-tension of the shoes. To do this, remove the handbrake lever gaitor and undo the two 10mm nuts.
 +
Lift the car up and remove the rear wheels. Now get a torch and look through the wheel bolt holes to see inside the drum. You are looking for a circular knurled nut around a thread. You need to wind this in so the shoes are nowhere near the drum surface.
 +
Now undo the 6mm alan bolt from the disc, take a hammer and hit the drum/hub part of the disc a couple of times to 'shock' it loose, but make sure you don't hit the wheel spigot or the actual disc. You should now be able to remove the disc
 +
 
 +
When you come to put new discs on, just wind the shoes right out so they are pushed right against the disc, and then undo them 6-7 turns using the adjuster. Now pull up the handbrake 3 clicks and tighten the 10mm nuts so that the shoes only just touch the drum, enough to slightly retard the wheel from moving.
 +
 
 +
==Replacing Fluid==
 +
 
 +
Fresh brake fluid gives a sharper brake response and can cause all manner of brake-related niggles. But unlike engine oils, you don't change it by draining the system, but instead flush the old out with the new. This does lead to some wastage, as you need to pump good stuff all the way through the system and out again to know it's all new, but it's worth it. E30s need less than a litre to fully flush and replace the fluid.
 +
 
 +
This process is very similar to [[Brakes#Bleeding|bleeding]], and the same process applies. However, since we are pushing out (or flushing) fluid, have a container ready to catch the old fluid as it spills from the system.
 +
 
 +
Work systematically. Undo the bleed screw on each [[Brakes#Calipers|caliper]] or [[Brakes#Cylinders|cylinder]] in turn and drain the fluid slowly using the same method as bleeding, but DO NOT get fluid on the paintwork of the car.
 +
 
 +
As you drain each wheel in turn, pour fresh fluid into the [[Brakes#Reservoir|reservoir]]. Keep expelling fluid until it changes colour, then tighten up the bleed screw on that wheel and move to the next.
 +
 
 +
When you've done all four wheels, test the pedal response. If it's still soft, [[Brakes#Bleeding|bleed]] each wheel again in turn to remove any trapped air in the system.
 +
 
 +
==Replacing Rear Shoes==
 +
 
 +
Since all cars have shoes (for [[Brakes#Drums|drums]] and [[Brakes#Discs|disc handbrakes]]) this procedure applies to both.
 +
 
 +
Chock the front wheels and lift the car onto jack stands. Take off the hand brake.
 +
 
 +
If fitted, unbolt the [[Brakes#Caliper|caliper]] and hang it up to something so you don't stress the hose.
 +
 
 +
Undo the [[Brakes#Discs|disc]] holding bolt, in between the wheel nut holes, or the [[Brakes#Drums|drum]] bolt.
 +
 
 +
Wiggle the disc or drum off the hub. If it won't budge then peek inside the disc hub from the top, u should see a bullet type thing with a little knurled wheel; this is the [[Brakes#Handbrake|handbrake]] adjuster. Wind it in to slacken the shoes, and the disc/drum should slip off.
 +
 
 +
The [[Brakes#Shoes|shoes]] themselves are connected to the brake backing plate via 2 spring loaded pegs, one for each shoe. They need to come off.
 +
 
 +
Then detach the spring or [[Brakes#Cylinders|cylinder]] from the top and remove the shoes.
 +
 
 +
The new ones need a light sanding before being fitted, the bolts with the springs should all be in the handbrake kit provided with the shoes
 +
 
 +
Shoes have the narrow nip at the bottom and the wider nip at the top.
 +
 
 +
If you have pegged the shoes in with the spring pegs, then clip the tension spring (the one with the slight kink to it) on the bottom holes, the kink needs to point downwards to clear the hub.
 +
 
 +
Check properly that you have located the shoes into the cable ratchet as it should be. Then position the shoes so they look parallel, fix the bullet back into position, and wind it out one full turn.
 +
 
 +
Then reattach the top spring or cylinder, give it a smothering (light) of copper grease and put the disc or drum back on
 +
 
 +
If you have discs, it may be worth changing your rear brake [[Brakes#Pads|pads]] at the same time.
 +
 
 +
Then [[Brakes#Adjusting_Handbrake|adjust the handbrake]].
 +
 
 +
==Adjusting Handbrake==
 +
''Main article: [[Handbrake]]''
 +
 
 +
Although the handbrake is cable operated, adjustment is made at the wheel. Any adjustment at the lever is considered a bodge, and will result in uneven shoe wear and shortened brake life.
 +
 
 +
Cars fitted with rear drums have self-adjusting handbrakes. If your rear drum handbrake isn't working, remove the [[Wheels|wheel]] and [[Brakes#Drums|drum]] and inspect the mechanism. Lubrication of the mechanism is often all that is needed.
 +
 
 +
For rear disc brakes, the handbrake is adjusted by rotating a small cog behind the disc, which is only accessible through a wheel stud hole. Learn more about [[Handbrake#Adjustment|adjusting the handbrake]].
 +
 
 +
==Rebuilding Calipers==
 +
 
 +
Over time the rubber components that make up the seals in the calipers will perish and fail. You can restore them to fully-working condition by removing, dismantling, cleaning and rebuilding them. Learn more about [[Caliper_Rebuild|rebuilding your calipers]].
 +
 
 +
=Common Problems=
 +
 
 +
==Soft Brakes==
 +
 
 +
Spongy pedal is flex somewhere in the system, failed rubber hoses or air in the system, or contaminated fluid.
 +
 
 +
The most common cause for soft brakes is [[Brakes#Air|air]] in the brake lines, which can be introduced when new pads have been fitted and the air hasn't been completely removed.
 +
 +
[[Brakes#Bleeding|Bleed]] the brakes first to see if this eliminates the spongy feel. If not, check for leaks, give the brake lines and pipes a good check over for a fluid stains. If no stains or leaks are found,  get someone to check the [[Brakes#Brakes_Hoses|brake hoses]] while the brake pedal is being pushed hard, to see if any of the hoses swell up into a blister.
 +
 
 +
If the softness persists, change the brake fluid and re-bleed the system.
 +
 
 +
==Air==
 +
 
 +
Air in a hydraulic system is a big problem, because air can be compressed. Considering the sorts of pressures involved in a braking system, any air in there would be compressed without transferring any force through the system. In short, no brakes.
 +
 
 +
Getting the air out is known as [[Brakes#Bleeding|bleeding]], and is one of the most frustrating parts of brake maintenance. Having [[Brakes#ABS|ABS]] only makes things worse, since the ABS pump is notoriously difficult to bleed.
 +
 
 +
==Pulling==
 +
 
 +
Pulling shows up as an aggressive twist of the steering wheel the moment the brakes are applied. If this is happening to you, the first point of call should be the [[Brakes#Calipers|calipers]], which are most likely sticking. To test, immediately after a driving session examine each wheel in turn for excessive heat. DO NOT touch the discs, as they will be very hot, but if you feel that one [[Wheels|wheel]] is hotter than the rest, then the caliper on that wheel will benefit from a [[Brakes#Rebuilding_Calipers|rebuild]].
 +
 
 +
==Squealing==
 +
 
 +
Squealing from the brakes can be caused by a number of things, only one of which is bad. The first thing to check is the condition of the [[Brakes#Pads|pads]]. If these are worn, replace them immediately. If they're not, check the heat-shields on the rear, and make sure they haven't been bent in such a way that they are touching the disc.
 +
 
 +
If you recently changed your discs and pads, and are now getting squealing, ensure that the rear of the pads were covered with  copper grease where they fit into the carrier, and that the anti-rattle springs are not touching the disc.
 +
 
 +
If the pads were fitted correctly there should be no squeal; however, some brands have been known to squeal when new, and require some aggressive driving to take off the top surface.
 +
 
 +
==Stuck Brakes==
 +
 
 +
Brakes that stick often show themselves as a reluctance for the car to roll, and an extremely stiff pedal. There are multiple causes, and it is important to be systematic as you check the system.
 +
 
 +
To start with, allow the car to sit for a few hours for everything to cool down, and then go out for a very gentle drive without touching the brakes at all. Like any emergency situation, use the gears and handbrake to slow you down as needed, and don't drive too fast. Just move the car around for a few minutes.
 +
 
 +
When ready, bring the car to a stop (WITHOUT touching the brake pedal), and apply the handbrake. Get out, and place your hands on each wheel to feel for heat. You are testing for heat build-up, which will indicate whether one brake or the entire system is sticking.
 +
 
 +
If more than one wheel feels excessively hot, the fault is almost guaranteed to lie with the [[Brakes#Master_Cylinder|master cylinder]], which should be replaced.
 +
 
 +
If only one wheel is hot, inspect the [[Brakes#Brake_Hoses|hose]] and [[Brakes#Brake_Lnes|line]] for kinks, dents or crimps that would stop the fluid from moving through. If the line is showing signs of corrosion, there is a chance that rust inside has reduced the diameter of the pipe, slowing the fluid down. To test, undo the [[Brakes#Bleeding|bleed screw]] on that wheel. If the brake now releases and spins freely, then there is a blockage in the hose or line, which should be replaced.
 +
 
 +
If bleeding does not solve the issue, the problem lies with the brake mechanism itself. On [[Brakes#Drums|drum]] brakes, the drum must be removed and the mechanism inspected. If the cylinder moves freely when disconnected, the problem will be a rusty pivot or broken spring. On [[Brakes#Calipers|disc]] brakes, the fault is normally the caliper piston or the carrier sliders; if these get dirty then the brake cannot slide freely, and will get stuck in position.
 +
 
 +
Unbolt the caliper but don't disconnect its supply hose. Make sure it can move on is sliders freely with no resistance (if there is, clean it with warm soapy water but do not use any metal brushes). Pump the brake pedal to extend the caliper piston, but leave the pads in place to stop the piston coming out completely.
 +
 
 +
Check the condition of the rubber dust seal around the piston for holes/integrity and then fold it back and have a look at the condition of the chromed outer surface of the piston. If water has got at the surface of the chrome plating, cracks and flakes will form and damage the inner pressure seal and jam the piston. If the piston is ok but the rubber components are perished, you can buy just the seals instead of a whole new caliper, and [[Caliper_Rebuild|rebuild your calipers]]. However, if the piston is damaged, the caliper must be replaced.
 +
 
 +
If the caliper looks good, use a G-clamp and a small piece of wood to press the piston back in. If the caliper refuses to return, undo the bleed screw. If the caliper is still very reluctant, a full rebuild is necessary.
 +
 
 +
=Upgrades=
 +
''Main article: [[Brake_Upgrades|Brake Upgrades]]
 +
 
 +
The stock braking system fitted to the [[325i]] and all [[Touring]]s is a perfectly capable braking system for the E30, no matter how aggressively you drive. However, if you're planning to race your E30, or you've [[Engines#Upgrades|changed your engine]] to something more powerful, it's worth looking at your options.
 +
 
 +
There are bolt on kits available which range from 280mm discs with 4 pots to fit under standard 15inch BBS cross spoke wheels to larger kits with 310mm discs. It is possible to retrofit 4 pot calipers from other cars with the use of custom brackets etc. For many track applications simple performance compound pads and grooved disc upgrades will suffice. It is also worth fitting braided brake lines as these hold pressure better when the pedal is pressed hard and keep your system in top performance with regular regular [[Brakes#Servicing|servicing]].
 +
 
 +
Learn more about [[Brake_Upgrades|upgrading your brakes]].
 +
 
 +
[[Category: Technical]]
 +
[[Category: Brakes]]

Latest revision as of 17:27, 23 June 2013

You can have all the power in the world, but at some point you're going to want to slow your E30 down. When it's time for some middle-pedal action, get to know what your brakes up are up to.

Overview

All E30s are fitted with a hydraulic braking system. When the pedal is pressed, fluid is pressurised by the Master cylinder to send fluid to each wheel. To help, extra pressure is generated by the servo, driven by the engine. This pressurised fluid powers the braking system, which on all E30s comprises of front discs and either rear discs or drums. A the front, the brake fluid will pressurise two calipers, which will squeeze pads against the discs to convert the kinetic energy of the rotating disc into heat. To a smaller degree, cylinders on the rear will press shoes against the inside face of the drums to achieve the same effect.

When you want the car to stay still, a cable-operated handbrake will lock the rear shoes in place. On cars fitted with rear discs, small handbrake shoes work on the inside of the rear disc.

Keeping all of the components fresh and leak free will help massively in preventing car/tree interactions.

Components

Brake Pedal

The brake pedal forms part of the pedal box, and it may surprise you to know that it is how the brakes are activated by the driver. It is connected to the master cylinder through a pull rod, which can be adjusted to control pedal height. There's a small rubber buffer on the lowest part of the bracket that holds the brake light switch, and the rod should be shortened until the arm of the pedal all but touches this buffer.

To adjust the brake pedal, slacken off the lock nuts and turn the pull rod using a 7mm open-ended spanner on the flats near the clutch pedal to adjust, until the brake pedal only has a small bit of upwards free movement to its stop. One end of this rod has a reverse thread, so turning it changes its length.

Be careful though. If you over-tighten things, so that the pedal is touching the buffer and moving the master cylinder push rod, the brakes are likely to lock on.

Brake Light Switch

The brake light switch is mounted to a frame just above the pedal arm, and is held in place with two small plastic tabs on its sides. It goes directly to the main loom, where it feeds the rear lights, and the Check Panel and Cruise Control if fitted. For cars fitted with a Check Panel, it is normal for the brake fault light to glow the moment the ignition is turned on; it will turn off the moment the brake pedal is pressed.

Brake Servo

The brake servo powers the master cylinder, making it easier on your braking foot. However, it does not improve braking performance; it simply takes the weight off your leg by replacing muscles with vacuum pressure.

It gets this extra pressure via hoses from the rubber boot on the engine intake system. Earlier cars used a very complex arrangement of hoses to supply pressure, for reasons unknown, while later systems were significantly simpler, using just one pipe from the throttle body to the servo.

When changing your engine or replacing your rubber boot, it is very common to find that you don't have the right number of holes to correctly connect your brake servo. Over the years, BMW tried all sorts of plumbing solutions to provide vacuum to the brake servo, and this resulted in a large variety of rubber boots on the market. If you find that your rubber boot doesn't have the right number of holes, simply connect all the other hoses to the brake servo in the most direct way possible, and plug any other holes.

To check the condition of your servo, pump the brake pedal a few times with the engine off to get rid of any vacuum in the the servo. Then press your foot on the brake pedal and hold pressure on it as you start the car. You should feel the pedal drop a bit as the vacuum builds. If it does not you may have a vacuum leak or other servo problem.

Servos are interchangeable across the entire E30 range. For those attempting an M50 or M52 engine swap, a Renault Clio (2000 or later) brake servo is a smaller alternative than the standard unit, and bolts straight up. It only requires a spacer at the end of the pull rod to remove pedal slack. This is a much better option than the old Mk 1 Gold servo.

Intake Valve

Because the brake servo receives air pressure from the Intake, it important for that pressure not to be lost. For that reason, a one-way valve is fitted in the hoses between the rubber boot and the brake servo. Occasionally this valve can fail, leading to loss of braking force.

Master Cylinder

To transfer pedal power into fluid pressure, your car is fitted with a Master Cylinder. Imagine it like a big nurse's syringe, but with four holes on it instead of one. As you press the pedal, fluid is compressed through these four holes to each wheel in turn.

The standard E30 Master cylinder is a 19mm unit, and is the same across all facelift cars. There is no difference between ABS and non-ABS cars either; cars fitted with ABS simply block up the rear two ports on the master cylinder.

If the pedal sinks slowly to the floor under constant / light pressure then you have a leak, normally this is an internal master cylinder seal.

Reservoir

The reservoir that holds the brake fluid sits on top of the master cylinder. It is a simple container, and simply pushes into the top of the master cylinder; it does not have any screws or bolts holding it in place. It also houses the Brake Fluid Level Sensor, which is the first place to check if your brake warning light glows on the dash cluster.

Leaks from the Reservoir are usually caused by a perished rubber seal between the reservoir and the cylinder. To fix, simply pull the reservoir up firmly, replace the seal and relocate the reservoir.

Pressure Valve

Underneath the Master Cylinder is a pressure valve, for the rear brakes. Its purpose is to ensure that the rear brakes don't receive as much pressure as the fronts, because this will cause the rears to lock up which is never fun on a RWD car. Well it is, but you get the point.

The Pressure Valve was offered in two flavours; an enormous thing as big as the Master Cylinder for earlier cars, and a small metal block for later cars. These are entirely interchangeable, although they very rarely need replacing.

Brake Fluid

Main article: Brake Fluid

The fluid that pulses through your braking system is the most crucial component. Just like oil for the engine, fluid needs to be changed at regular intervals to keep the brakes working as they should. If you don't, moisture creeps into the system, which can cause pressure problems as well as internal corrosion.

DOT 4 braking fluid should be used, although DOT 5.1 non-silicon is an acceptable alternative. It is essential to use non-silicon fluids as it can cause failure of the rubber seals in the calipers. Learn more about .

Brake Lines

Steel brake lines run from the master cylinder to each wheel in turn. They are clipped to the body of the vehicle every 300mm (approx.) and use 10mm fittings.

Over time, these steel lines will obviously rust due to all the mud at salt thrown underneath the car. and can cause lost of braking power at the wheel end or, if they burst, total brake failure caused by loss of system pressure. If the MOT man tells you to replace your brake pipes, do what he says.

While replacements are still available from BMW, it can be a lot less of a headache to make your own pipes from cunifer, and bend them yourself to suit. Cunifer doesn't rust, so well-made pipes should last the lifetime of the vehicle.

Brake Hoses

Flexible brake hoses connect the brake components to the brake lines, allowing the [Wheels|wheel]] a degree of travel as well as reducing vibrations through the system.

While the brake hoses are screwed together using standard fittings, they are subjected to such harsh road conditions that it's almost impossible to remove them without damaging them, even with the correct tools. For the sake of safety, it is best to consider brake hoses disposable items.

Brake hoses don't have to split to cause problems to the system. Over time the rubber they are made of can weaken and relax, allowing them to balloon up under braking pressure. This will stop the brake on that wheel from working properly, so always check the condition of the hoses first when looking for brake problems.

Calipers

All E30s were fitted with front disc brakes, which employ a caliper to squeeze two pads to each side of a metal discs. This resulting friction converts the discs spinning force into heat, slowing the car down. The caliper is mounted to a carrier, which allows the caliper to "float" over the disc.

Two types of FRONT calipers were fitted. M10- and M40-engined cars were fitted with smaller calipers that worked on solid discs, while the more powerful M20- and M42-engined cars were capable of accepting vented discs, and therefore had wider calipers.

Most calipers were made by ATE, although some parts were sourced by Girling and it is impossible to know what may have been fitted to any particular car without looking. The part number should be stamped on the curved face on the back of the calipers. However, the make of caliper does not affect the purchasing of pads. However, it is important if you are buying parts to rebuild your calipers.

It is possible to fit the wider calipers and vented discs to all E30s. Parts sourced from the more powerful E30s will bolt straight on. If you are interested in much more powerful braking systems, learn more about upgrading the brakes.

The REAR calipers, as fitted to all M20-engined cars, as well as all Tourings and Cabriolets, are fully interchangeable across all vehicles although Touring calipers have bigger pistons. If your car has drums at the back, it is possible to convert to discs using bolt-on components. Learn more about converting to rear discs.

To rebuild your rear calipers, you will need two rebuild kits (34211153194) which contain a piston seal, dust seal and a circlip.

Discs

Two different discs were fitted to the front of E30s; solid discs for the smaller engines, and wider, vented discs for the more powerful versions. These discs are matched to the calipers; a solid disc should not be fitted to a 325i because it will cause excessive piston travel and ultimately brake failure, while a vented disc will not fit to a standard 318i because it simply won't get inside the caliper.

There is no benefit to using drilled or grooved discs on an E30, and it is heavily recommended that you do not. Drilled discs in particular are structurally weakened by the drilling, which leads to cracks and ultimately brake failure. The standard discs fitted to E30s are more than sufficient, even for the common engine swaps of M30 and M50 engines.

Learn more about replacing your discs.

Pads

The pads are made of a friction material which rubs against the discs when the brakes are pressed. Over time, this friction material will wear down, leaving you with a flat metal pad grinding and gouging the disc surface. It is very important that you change your discs BEFORE you get to this point, as it not only ruins the discs but also leads to total brake failure.

All front pads are interchangeable on E30s, although some simple upgraded pads are available. Textar and Pagid pads are recommended alternatives.

Check the condition of the discs before you change the pads. E30 discs only last the life of two or three sets of pads.

Learn more about replacing your pads.

Pad Wear Sensor

Only one pad of the four at the front (and the same at the back if you have rear discs) is fitted with a wear sensor. Pads don't wear completeley evenly, so to be on the safe side, the light usually comes on when there are several thousand miles of wear left in the pads. However, you should have a look at the pads to check that none are nearly down to the metal. There is also a well-known fault in the instrument cluster that puts the pad wear light on intermittently.

Drums

The back end of the small-engined saloons were fitted with drum brakes. Unlike calipers, the braking force is applied to the inside face of the drum, whereby a brake cylinder pushes out two curved shoes. These shoes rub against the drum to create friction, and therefore heat.

Although the rear wheels are driven, they receive a let less braking force than the front wheels due to the pressure valve, and therefore a less sophisticated braking system is needed.

However, drums are particularly irksome when it comes to servicing and repairing, with many E30 owners choose to convert to rear discs. Parts availability, and ease of servicing in the future, make this a very popular modification. Learn more about converting to rear discs.

Cylinders

To make the shoes press against the drum, a cylinder is fitted. The cylinder is little more than two rods, pushed out and in by the changing fluid pressure in the system. When the brake pedal is pressed, the rods in the cylinder extend, forcing the face of the shoes against the drum.

Despite the simplicity, the relative size of cylinders makes them fragile, and for peace of mind they should be replaced at the same time as the shoes.

Shoes

Shoes in drum brakes come in two flavours. For rear drum brakes, a large pair of shoes is required. These are simple metal curves with a friction pad on the outside face, designed to make maximum contact with the drum.

The shoes are joined at their base with a high-tension coil spring. When detaching this spring, only stretch it by hooking a piece of fine but strong wire around the ends and pulling on the wire, otherwise you are likely to lose the skin off your fingertips.

For cars with rear discs, a smaller pair of shoes is fitted to the inside 'bell' of the disc. These are for the handbrake, and therefore do not need to be so large.

Handbrake

Main article: Handbrake

Rear disc handbrake setup

The handbrake is a cable-operated mechanism separate from the hydraulic brake setup. On all cars, the handbrake controls shoes on the rear wheel, regardless of whether the car has discs or drums.

The handbrake lever is bolted to the transmission tunnel inside the car, and is covered with a gaiter. If you remove this gaitor, you will see that the arm sits on two small metal contacts which power the handbrake light, which should light when the handbrake is lifted.

In the middle of the lever are two threaded rods with nuts. These rods attach to two cables that run from the handbrake lever to each rear wheel. These cables run through protective sleeves to the rear wheels, where they will pull on the handbrake mechanism; a simple mechanical arm that pulls the shoes outwards to rub against the inside edge of the disc or drum. These cables are specific to disc and drum brakes, and if they need to be replaced, they are a massive headache due to their construction. Brute force and a blowtorch is often the only way to get old cables off the car.

With drum brakes, the handbrake is self-adjusting, and any handbrake issues are usually cable-related or rusty mechanisms. With rear discs, the bottom of the shoes are pushed by the handbrake and the top are pushed by a static adjuster. If you only adjust the handbrake at the lever then you don't get full shoe contact and you'll get odd wear and a reduced efficiency handbrake. Learn more about adjusting the handbrake.

Z3 handbrake shoes from a 6-cylinder model fit rear-disc E30 models. Use the Z3 shoes, pins, retaining springs, pull off springs and adjuster, but retain the E30 expander. This will result in a much firmer, more solid handbrake.

ABS

Main article: ABS

The Anti-Lock Braking System fitted to some E30s is a relatively simple system designed to, well, stop the wheels from locking up. To do this, the pressure to the brakes is pulsed rather then constantly applied, applying a hard then soft force to allow the wheel to still rotate. While this may seem daft in straight-line braking, for cornering it allows the front wheels to still turn the car away from its current direction, so that you don't slide straight into a tree in a cloud of smoke.

This pulsing pressure is applied through an ABS pump, which accepts fluid straight from the Master Cylinder and sends it onwards to each wheel in turn. Because of this, fewer fluid pipes are needed so for ABS vehicles, the rear ports of the Master Cylinder are blanked off.

On each wheel an ABS sensor is fitted, which tracks the rotation speed of each wheel. A sensor is also fitted in the pump to measure incoming braking pressure. When the brake pedal is applied, the ABS ECU will immediately read from each sensor, and if the pressure is hight enough, the ABS pump will pulse. This often feels strange the first time its used, and many new E30 owners spend subsequent wasted hours looking for braking faults. Don't worry, you just have ABS.

For track and race preparation, ABS can be easily removed with very little work. The Master Cylinder does not need to be replaced, but brake lines need to be attached to the rear ports on the cylinder to feed the appropriate wheels.

If you're having issues, learn more about ABS Problems.

Servicing

No brakes = no car. But you don't want to get into a position where you don't have any brakes, so preventative maintenance MUST be done regularly. The following parts should be inspected and replaced regularly

Bleeding

Bleeding is the process of expelling air from the system, and is necessary if you've disconnected any of the hydraulic components.

The process is relatively simple, but requires two people. If you have a one-man bleeding kit, follow the instructions provided.

Bleeding is done by releasing a special screw on each brake, called a bleed screw. The brake pedal is then pressed to push air out, and the screw retightened. In practice, several pedal pumps are required on each wheel, requiring co-operation between the unscrewer and the pedal-pusher. If the pedal is released while the screw is undone, air will be sucked back into the system and you will have to start all over again, so choose an assistant you can both trust and punch when things go wrong.

To start, locate the bleed screw on each caliper or cylinder and soak it in a good penetrating oil (like WD40) repeatedly for up to a week before attempting to bleed. Bleed screws are notoriously fragile, and if you break one they are becoming increasingly expensive to replace from BMW.

  1. When ready, crack off the bleed screw with a proper brake spanner to reduce the risk of rounding off the bolts.
  2. Unscrew one quarter turn
  3. Have assistant press AND HOLD the brake pedal
  4. Retighten bleed screw
  5. Have assistant release brake pedal
  6. Repeat steps 2-5 until fluid seeps from the bleed screw. At this point, retighten the screw fully and move to the next wheel.

When you have bled each wheel in turn, check the pedal for sponginess. If the pedal is still too soft, re-bleed all four wheels again in the same sequence. If the pedal still feels soft, learn more about soft brakes.

Replacing Pads and Discs

When working on brakes, ensure that any wheels touching the ground are chocked, so that they cannot move.

For FRONT discs: The first step is to lever the pads and the caliper away from the disc. do this by inserting a screwdriver behind the pad (there should be a small lip on the pad you can get leverage on) and pulling the s/driver towards you.

Then loosen the caliper bolts. I recommend using a hex socket as opposed to an allen wrench. The allen bolts are 7mm and are in there pretty tight. They loosen fairly easliy with a ratchet. Once the bolts are all the way loose, simply pull the caliper off the rotor. Don't let it hang from the brake line though; support it on a jackstand, or suspend it with stiff wire from the suspension spring. Extract the pads.

Now remove the small 6mm hex screw in the face of the disc, and give the disc an allmighty wallop with a hammer to get it off the hub.

When you put the new stuff on, squeeze the piston on the caliper back in with some large swan leg pliers, clean all the dirt off the caliper carrier with a wire brush, and apply plenty of copper grease to the back of the pads (not the face that goes on the disc!)

Installation is opposite of removal. Remember to pump the pedal before driving away, to return the caliper piston to its proper location.

For REAR discs:

First you need to take out the pre-tension of the shoes. To do this, remove the handbrake lever gaitor and undo the two 10mm nuts. Lift the car up and remove the rear wheels. Now get a torch and look through the wheel bolt holes to see inside the drum. You are looking for a circular knurled nut around a thread. You need to wind this in so the shoes are nowhere near the drum surface. Now undo the 6mm alan bolt from the disc, take a hammer and hit the drum/hub part of the disc a couple of times to 'shock' it loose, but make sure you don't hit the wheel spigot or the actual disc. You should now be able to remove the disc

When you come to put new discs on, just wind the shoes right out so they are pushed right against the disc, and then undo them 6-7 turns using the adjuster. Now pull up the handbrake 3 clicks and tighten the 10mm nuts so that the shoes only just touch the drum, enough to slightly retard the wheel from moving.

Replacing Fluid

Fresh brake fluid gives a sharper brake response and can cause all manner of brake-related niggles. But unlike engine oils, you don't change it by draining the system, but instead flush the old out with the new. This does lead to some wastage, as you need to pump good stuff all the way through the system and out again to know it's all new, but it's worth it. E30s need less than a litre to fully flush and replace the fluid.

This process is very similar to bleeding, and the same process applies. However, since we are pushing out (or flushing) fluid, have a container ready to catch the old fluid as it spills from the system.

Work systematically. Undo the bleed screw on each caliper or cylinder in turn and drain the fluid slowly using the same method as bleeding, but DO NOT get fluid on the paintwork of the car.

As you drain each wheel in turn, pour fresh fluid into the reservoir. Keep expelling fluid until it changes colour, then tighten up the bleed screw on that wheel and move to the next.

When you've done all four wheels, test the pedal response. If it's still soft, bleed each wheel again in turn to remove any trapped air in the system.

Replacing Rear Shoes

Since all cars have shoes (for drums and disc handbrakes) this procedure applies to both.

Chock the front wheels and lift the car onto jack stands. Take off the hand brake.

If fitted, unbolt the caliper and hang it up to something so you don't stress the hose.

Undo the disc holding bolt, in between the wheel nut holes, or the drum bolt.

Wiggle the disc or drum off the hub. If it won't budge then peek inside the disc hub from the top, u should see a bullet type thing with a little knurled wheel; this is the handbrake adjuster. Wind it in to slacken the shoes, and the disc/drum should slip off.

The shoes themselves are connected to the brake backing plate via 2 spring loaded pegs, one for each shoe. They need to come off.

Then detach the spring or cylinder from the top and remove the shoes.

The new ones need a light sanding before being fitted, the bolts with the springs should all be in the handbrake kit provided with the shoes

Shoes have the narrow nip at the bottom and the wider nip at the top.

If you have pegged the shoes in with the spring pegs, then clip the tension spring (the one with the slight kink to it) on the bottom holes, the kink needs to point downwards to clear the hub.

Check properly that you have located the shoes into the cable ratchet as it should be. Then position the shoes so they look parallel, fix the bullet back into position, and wind it out one full turn.

Then reattach the top spring or cylinder, give it a smothering (light) of copper grease and put the disc or drum back on

If you have discs, it may be worth changing your rear brake pads at the same time.

Then adjust the handbrake.

Adjusting Handbrake

Main article: Handbrake

Although the handbrake is cable operated, adjustment is made at the wheel. Any adjustment at the lever is considered a bodge, and will result in uneven shoe wear and shortened brake life.

Cars fitted with rear drums have self-adjusting handbrakes. If your rear drum handbrake isn't working, remove the wheel and drum and inspect the mechanism. Lubrication of the mechanism is often all that is needed.

For rear disc brakes, the handbrake is adjusted by rotating a small cog behind the disc, which is only accessible through a wheel stud hole. Learn more about adjusting the handbrake.

Rebuilding Calipers

Over time the rubber components that make up the seals in the calipers will perish and fail. You can restore them to fully-working condition by removing, dismantling, cleaning and rebuilding them. Learn more about rebuilding your calipers.

Common Problems

Soft Brakes

Spongy pedal is flex somewhere in the system, failed rubber hoses or air in the system, or contaminated fluid.

The most common cause for soft brakes is air in the brake lines, which can be introduced when new pads have been fitted and the air hasn't been completely removed.

Bleed the brakes first to see if this eliminates the spongy feel. If not, check for leaks, give the brake lines and pipes a good check over for a fluid stains. If no stains or leaks are found, get someone to check the brake hoses while the brake pedal is being pushed hard, to see if any of the hoses swell up into a blister.

If the softness persists, change the brake fluid and re-bleed the system.

Air

Air in a hydraulic system is a big problem, because air can be compressed. Considering the sorts of pressures involved in a braking system, any air in there would be compressed without transferring any force through the system. In short, no brakes.

Getting the air out is known as bleeding, and is one of the most frustrating parts of brake maintenance. Having ABS only makes things worse, since the ABS pump is notoriously difficult to bleed.

Pulling

Pulling shows up as an aggressive twist of the steering wheel the moment the brakes are applied. If this is happening to you, the first point of call should be the calipers, which are most likely sticking. To test, immediately after a driving session examine each wheel in turn for excessive heat. DO NOT touch the discs, as they will be very hot, but if you feel that one wheel is hotter than the rest, then the caliper on that wheel will benefit from a rebuild.

Squealing

Squealing from the brakes can be caused by a number of things, only one of which is bad. The first thing to check is the condition of the pads. If these are worn, replace them immediately. If they're not, check the heat-shields on the rear, and make sure they haven't been bent in such a way that they are touching the disc.

If you recently changed your discs and pads, and are now getting squealing, ensure that the rear of the pads were covered with copper grease where they fit into the carrier, and that the anti-rattle springs are not touching the disc.

If the pads were fitted correctly there should be no squeal; however, some brands have been known to squeal when new, and require some aggressive driving to take off the top surface.

Stuck Brakes

Brakes that stick often show themselves as a reluctance for the car to roll, and an extremely stiff pedal. There are multiple causes, and it is important to be systematic as you check the system.

To start with, allow the car to sit for a few hours for everything to cool down, and then go out for a very gentle drive without touching the brakes at all. Like any emergency situation, use the gears and handbrake to slow you down as needed, and don't drive too fast. Just move the car around for a few minutes.

When ready, bring the car to a stop (WITHOUT touching the brake pedal), and apply the handbrake. Get out, and place your hands on each wheel to feel for heat. You are testing for heat build-up, which will indicate whether one brake or the entire system is sticking.

If more than one wheel feels excessively hot, the fault is almost guaranteed to lie with the master cylinder, which should be replaced.

If only one wheel is hot, inspect the hose and line for kinks, dents or crimps that would stop the fluid from moving through. If the line is showing signs of corrosion, there is a chance that rust inside has reduced the diameter of the pipe, slowing the fluid down. To test, undo the bleed screw on that wheel. If the brake now releases and spins freely, then there is a blockage in the hose or line, which should be replaced.

If bleeding does not solve the issue, the problem lies with the brake mechanism itself. On drum brakes, the drum must be removed and the mechanism inspected. If the cylinder moves freely when disconnected, the problem will be a rusty pivot or broken spring. On disc brakes, the fault is normally the caliper piston or the carrier sliders; if these get dirty then the brake cannot slide freely, and will get stuck in position.

Unbolt the caliper but don't disconnect its supply hose. Make sure it can move on is sliders freely with no resistance (if there is, clean it with warm soapy water but do not use any metal brushes). Pump the brake pedal to extend the caliper piston, but leave the pads in place to stop the piston coming out completely.

Check the condition of the rubber dust seal around the piston for holes/integrity and then fold it back and have a look at the condition of the chromed outer surface of the piston. If water has got at the surface of the chrome plating, cracks and flakes will form and damage the inner pressure seal and jam the piston. If the piston is ok but the rubber components are perished, you can buy just the seals instead of a whole new caliper, and rebuild your calipers. However, if the piston is damaged, the caliper must be replaced.

If the caliper looks good, use a G-clamp and a small piece of wood to press the piston back in. If the caliper refuses to return, undo the bleed screw. If the caliper is still very reluctant, a full rebuild is necessary.

Upgrades

Main article: Brake Upgrades

The stock braking system fitted to the 325i and all Tourings is a perfectly capable braking system for the E30, no matter how aggressively you drive. However, if you're planning to race your E30, or you've changed your engine to something more powerful, it's worth looking at your options.

There are bolt on kits available which range from 280mm discs with 4 pots to fit under standard 15inch BBS cross spoke wheels to larger kits with 310mm discs. It is possible to retrofit 4 pot calipers from other cars with the use of custom brackets etc. For many track applications simple performance compound pads and grooved disc upgrades will suffice. It is also worth fitting braided brake lines as these hold pressure better when the pedal is pressed hard and keep your system in top performance with regular regular servicing.

Learn more about upgrading your brakes.

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