Rear brake pressure regulating valve - removal, refitting and adjustment

Braking system / Rear brake pressure regulating valve - removal, refitting and adjustment

Note: Before starting work refer to the warning at the beginning of Section 2 concerning the dangers of hydraulic fluid.

Removal
1 A brake pressure regulator is fitted in the rear brake circuit of most models and its purpose is to prevent the rear wheels locking in advance of the front wheels during heavy application of the brakes. The regulator is also load sensitive in order to vary the pressure according to the load being carried. The regulator is located on the underbody, in front of the left-hand rear wheel.

2 Minimise fluid loss by first removing the master cylinder reservoir cap, and then tightening it down onto a piece of polythene, to obtain an airtight seal.

3 Chock the front wheels then jack up the rear of the car and support on axle stands (see “Jacking and vehicle support”).

4 Working beneath the car unhook the spring from the regulator.

5 Identify each hydraulic brake line for position, then unscrew the union nuts and withdraw the lines so that they are just clear of the regulator. Tape the ends of the brake lines to prevent entry of dust and dirt.

6 Unscrew the mounting bolts and withdraw the regulator from under the car.

Refitting
7 Before refitting the regulator check that the brake line apertures and sealing surfaces are clean.

8 Locate the regulator on the underbody, insert the bolts and tighten securely.

9 Remove the tape and wipe clean the ends of the hydraulic lines then insert them into their correct positions and tighten the union nuts. To ensure that the nuts are not crossthreaded, initially tighten them by hand only.

10 Hook the spring onto the regulator and adjustment roller.

11 Remove the polythene from the master cylinder then bleed the complete hydraulic circuit as described in Section 2.

12 Lower the car to the ground.

13 The initial operation of the regulator can be checked as follows Have an assistant depress the brake pedal rapidly and check that the regulator lever moves at the same time.

Adjustment
14 Checking and adjustment of the regulator is best left to a WV garage as special pressure gauges and spring tensioning tools are required. Adjustment is made by varying the spring tension, but this must be carried out by the garage.