The pressure regulator is attached to the frame.
It adjusts the brake fluid pressure in the rear wheel brake circuit depending on the vehicle load, which improves directional stability during braking.
By sensing the rear axle load through the load spring, the regulator limits the fluid pressure in the rear brake circuit.
If the regulator fails, it is replaced.
Important: after replacing the regulator or rear suspension components, the position of the load spring relative to the rear axle must be readjusted.
Drain the brake fluid from the rear circuit.
Disconnect the load spring from the rear axle.
Using a 12 mm wrench, loosen the two brake pipe unions.
Holding the bolts from turning with a 12 mm socket, use a 13 mm wrench to loosen the two nuts of the regulator mounting bolts.
Remove the bolts and take the regulator off the vehicle together with the bracket.
Using a 13 mm wrench, loosen the two nuts.
Remove the bracket from the regulator.
Using a 12 mm wrench, loosen the retaining bolt.
Remove the load spring.
Extract the pin.
Extract the lever shaft. Remove the lever.
After transferring the components to the new regulator, install it in the reverse order.
Important: bleed the brake system and adjust the regulator.
Adjusting the Brake Pressure Regulator
Using a 13 mm wrench, loosen the strut nut and disconnect the load spring from the rear axle. Lower the load spring.
Using a 14 mm wrench, loosen the lock nut of the adjusting bolt.
Using a 10 mm wrench, turn the adjusting bolt. Set the distance between the center of the bracket hole and the regulator axis.
The distance must be within:
- 28–32 mm — for 4×2 buses;
- 36–40 mm — for 4×4 buses;
- 13–17 mm — for other vehicle types.
Holding the adjusting bolt, tighten the lock nut.
Secure the lower end of the strut to the rear axle bracket.
Adjustment check: after adjustment, check the operation of the regulator. To do this, at a speed of 50–60 km/h on a firm, dry road surface, press the brake pedal firmly; an assistant should stand to the side and observe the wheels.
With a serviceable and correctly adjusted regulator, there should be a slight lead in locking of the front wheels relative to the rear wheels.
If the opposite occurs, loosen the lock nut of the adjusting bolt and turn the bolt out half a turn.
If the front wheels lock much earlier than the rear wheels, turn the adjusting bolt in half a turn and tighten the lock nut.
Materials and Tools Used
- New brake pressure regulator assembly with bracket (if necessary).
- Brake fluid recommended by the vehicle manufacturer (usually DOT-4).
- 10 mm, 12 mm, 13 mm, and 14 mm wrenches.
- 12 mm socket for holding the bolts.
- Container for draining brake fluid.
- Rags for removing brake fluid traces.
- Vernier caliper or ruler for checking the 13–40 mm distance.
- Brake bleeding aid (e.g., an assistant or a vacuum bleeding kit).
Recommendations: brake fluid is hygroscopic and aggressive to paintwork — if it gets on the body, rinse it off immediately with water. After replacing the regulator, be sure to bleed the rear circuit and check the connections for leaks. Perform the adjustment on a loaded vehicle, with normal tire pressure and on a level surface.