Brakes and Traction Control: Description and Operation

GENERAL
The car is equipped with two independent braking systems, one of which - the wheel brakes - is operated by the brake pedal and acts on all four wheels through an hydraulic system supplying two independent circuits from a tandem-type master cylinder.

The second system - the parking brake - is lever-operated and acts mechanically on both rear wheels.





Axle-Split Braking System
1. Master cylinder
2. Brake manifold and reducing valve.

Cars with ABS and models without ABS from 1992 on are equipped with an axle-split braking system. In this case, the rear circuit supplies the front brakes and the front circuit the rear brakes. The purpose of the reducing valve (which was added to the rear brakes on 1992 models) is to reduce the pressure in the rear circuit under severe braking conditions to prevent wheel lock.

The reducing valve incorporates a safety function which is associated with the front brakes. In the event of an hydraulic fault in the front brakes, the pressure to the rear brakes is maintained at its full, unreduced value.

The hydraulic braking system is of the dual-circuit type.

Note: All cars with ABS have an axle-split system.





Circuit Arrangement On Cars With Axle-split Braking System, With Or Without ABS
Supplied by the front section of the master cylinder, the secondary circuit serves the rear calipers.

Two brake pipes are run to a pressure-reducing valve, from there the pipes run to the ABS hydraulic modulator or, on cars without ABS, directly to the wheels. These variants are also equipped with a level warning switch in the brake fluid reservoir.

Brakes Applied





The caliper pistons are forced outward, pressing the brake pads against the discs, when the brakes are applied and the pressure in the master cylinder increases. The braking power varies in proportion to the pedal pressure. Outward movement of the pistons produces a lateral stress on the seals, which remains present while the brakes are on.
1. Seal
2. Piston housing
3. Brake piston

Brakes Released





The hydraulic pressure on the pistons is relieved when the pedal is released. In this system, in which there is no residual hydraulic pressure in the brake pipes, the stress in the seal is sufficient to return each piston by a certain amount, creating a clearance between pad and disc. Thus, the pads remain in a 'neutral' position at a certain distance from the disc, regardless of wear, and the brakes are self-adjusting.