- 1 Overview
- 2 Components
- 3 Servicing
- 4 Common Problems
- 5 Upgrades
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.
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.
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.
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.
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.
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.
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.
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 .
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.
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.
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.
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.
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.
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.
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 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.
Main article: Handbrake
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.
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.
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 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.
- When ready, crack off the bleed screw with a proper brake spanner to reduce the risk of rounding off the bolts.
- Unscrew one quarter turn
- Have assistant press AND HOLD the brake pedal
- Retighten bleed screw
- Have assistant release brake pedal
- 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.
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.
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
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.
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.
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.
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.
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 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.
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 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.
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.
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.