Brake distributor for Volkswagen Golf 2

Why the rear does not bear the full load

When braking, the vehicle’s weight shifts forwards. The rear axle becomes lighter, and lighter wheels lock up at a much lower pressure. However, a locked rear wheel causes the vehicle to lose stability: the rear end slips, and the car veers off course.

The pressure distributor therefore limits the pressure sent to the rear beyond a certain threshold, so that the front wheels always lock first. In the most sophisticated systems, it is load-sensitive: connected to the rear axle via a link or a spring, it measures the suspension travel and allows more pressure to be applied the heavier the vehicle is. This is why it is also known as a brake compensator or brake regulator.

The two types of failure, which are opposite in nature

• Stuck in the closed position: the rear receives almost no pressure. Braking distances increase significantly, especially when laden, and the rear brake linings no longer wear. This is the most insidious fault, as it produces no noise and develops gradually.
• Stuck in the open position: all the pressure goes to the rear. The rear wheels lock up under heavy braking, particularly when the vehicle is unladen and on a wet road, and the vehicle becomes unstable.
• Broken or misaligned servo linkage: on a load-sensitive system, a corroded or dislodged link rod locks the brake force distributor in a position that makes no sense.

In both cases, the check is carried out on a brake test bench, which measures the braking force on each wheel individually. This is the only objective method, and it is also what the MOT test checks for.

Adjustment and replacement

A load-sensing brake distributor is not a component that you simply fit and forget: it must be adjusted, with the vehicle unladen and the suspension in its normal position, by adjusting the length of its link rod or the preload on its spring. A new unit fitted without adjustment may well brake less effectively than the old one.

Take advantage of the removal to check the condition of the linkage and its joints, which are exposed underneath the vehicle and are prone to corrosion, and to inspect the pipes leading to the brake force distributor, which are often corroded in the same place. After refitting, bleed the entire rear brake circuit, then have the brake force distribution checked on a test bench: when it comes to braking, a test drive is of no value whatsoever.

A brake force distributor is not a T-joint

The term ‘brake force distributor’ covers two very different components in a braking system. The brake force distributor, the subject of this page, is an active component: it modulates the pressure sent to the rear. The T-joint, sometimes also referred to as a ‘distributor’, is a simple plumbing fitting that splits a pipe to the two wheels on an axle, without modulating the pressure in any way.

If you’re looking for the component that mechanically distributes braking force, you’ve come to the right place. If you’re looking for the fitting that splits a pipe, you’ll need to look under ‘brake line parts’.