Hydraulic Fluid Regulator Pressure Switch: Service and Repair

Removing and Installing Pressure Warning Switch


Removing




1. With the ignition switch in position 0, pull off both plugs at the pump assembly.

2. Evacuate all pressure from the system by pressing the brake pedal down about 25 times. The system is at zero pressure when the brake pedal feels hard as it is pressed.




3. Remove press. warning switch (No.1) with special tool 9524. Prevent the pump assembly from turning while loosening the switch.

Warning: first clean the area round the pressure warning switch and cover it with non-fluffy cleaning cloths to trap the small a- mount of residual brake fluid which emerges.


Installing

1. Screw in the pressure warning switch and tighten to a torque of 26 Nm (19 ftlb). Renew the O-ring if necessary. Prevent the pump assembly from turning while tightening.

Note
Wet the sealing ring with brake fluid only. Never use brake cylinder paste. Absolute cleanliness is essential. Use only non-fluffy cleaning cloths.




2. If there is an electrical fault at the pressure warning switch, always exchange hydraulic pump relay (no.3) as well.





3. Attach plug to pressure warning switch (arrow).

4. Partly bleed the booster circuit as follows:
Open the bleed valve at the pressure reservoir. Attach the electrical plug to the pump. As soon as brake fluid emerges free from air bubbles, pull off the electrical plug and close the bleed valve.
Next, charge the pressure reservoir completely. To do this, attach the electrical plug. As soon as the pump is heard to switch off, pull off the electrical plug and relieve the pressure completely at the pressure reservoir bleed valve. Slowly open the bleed valve and hold the bleed hose firmly.

Warning: a pressure of up to 180 bar is present at the valve.
Wear protective goggles and gloves.

5. Connect pressure gauge SW 9509 to the pressure reservoir and check the switching points of the pressure warning switch and also for leakage in the booster circuit. The precise working procedure. and desired values are stated in Pressure Tests On Booster Circuit under Testing and Inspection.

Notes

If necessary, top up the brake fluid level at intervals so that the fluid reservoir is not drained completely. The booster circuit must be at zero pressure when connecting and removing the pressure gage.

6. After testing and assembly work has been completed, correct the brake fluid level with the pressure reservoir completely filled.