Brakes

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.

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.

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.

ABS

Main article: ABS

For ABS vehicles, the rear ports of the Master Cylinder are blanked off.

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

Common Problems

Soft Brakes

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

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.

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.

Remember, bigger doesn't always mean better; massive discs with 4- or 6-pot callipers will add a massive amount of weight to your vehicle, especially its suspension, and you may have difficulty finding wheels that fit. It's often enough just to fit racing-spec pads and discs, and keep your system in top performance with regular servicing.

Learn more about upgrading your brakes.