General information about the brake system (BMW 5 Series E28)

All E28 models (with the "retro" body) are equipped with disc brakes at the front, and either drum or disc brakes at the rear. E34 models (with a modern body) have front and rear disc brakes. Both front and rear brakes are self-adjusting on all models. Some recent models are equipped with anti-lock braking system (ABS); it is described in Section General information about anti-lock braking system.

Hydraulic system

The hydraulic system consists of two separate circuits. The master cylinder has separate reservoirs for each of the two circuits, and if one circuit leaks or fails, the other will continue to operate.

Vacuum booster

The vacuum booster, which uses the vacuum and atmospheric pressure of the engine intake manifold to provide boost to the hydraulic brake system, is mounted on the engine compartment bulkhead.

E28 models are equipped with hydraulic power steering. This system uses hydraulic pressure from the steering pump to boost the braking system.

Parking brake

The parking brake is linked to the rear brakes and is operated by a cable via a lever located on the center console. The parking brake assembly on models with rear drum brakes is a self-adjusting part of the rear drum brake assembly. On models with rear disc brakes, the parking brake operates via a pair of brake shoes located in the center of the rear brake disc and is manually adjusted.

Brake pad wear warning system

The brake pad wear warning system is linked to a red warning light on the instrument cluster that illuminates when the brake pads are worn to the point where they need to be replaced. DO NOT IGNORE this warning light. If you do not replace the pads soon after this light comes on, your brake rotors will be damaged.



On some models, the brake pad wear warning system also includes a warning light that comes on only when the brake pedal is depressed to give you advance notice that the pads need to be replaced.

The wear sensor is attached to the brake pads. It is located on the left front wheel; some models also have a sensor on the right rear wheel. The wear sensor is part of a closed circuit. As soon as the pads wear down to the point of contact with the sensor, the disc begins to rub off the part of the sensor facing the disc. This wears the wire inside the sensor and lights up the red light on the instrument panel.

Always check the sensor when replacing the pads. If you replace the pads before the warning light comes on, the sensor may still be OK; if the signal has already come on, the sensor should be replaced.

Service

After completing any procedure that requires disassembling any part of the brake system, always perform a test drive to check the brakes before using the vehicle normally. Always test the brakes on a clean, dry, level surface. Otherwise, the test results will be inaccurate.

Check the brakes at different speeds, with light and strong pressure on the brake pedal. The car should stop evenly, without turning to one side. Avoid locking the brakes, as this leads to wheel slippage, reduces braking efficiency and reduces control of the car.

The condition of the tires, the vehicle load and the front wheel alignment angles also affect the operation of the brakes.

[The original version is on the portal BMWMAN.RU]