Rear brake pressure regulator — removal, installation and adjustment

See part number. Here.

Rear brake hydraulic pressure regulator ("witch") located on the bottom, between the rear suspension beam and the body (see photo).

Removing

Put the car on a four-post lift, apply the parking brake and turn off the ignition (four-column platform lift type P-178D-03 with a lifting capacity of 3.5 tons).

Raise the vehicle to a height convenient for work.

Unscrew the fittings of the brake pipes 1 and 2, Figure 16-1, from the rear brake pressure regulator 4 and install the plugs on the brake pipes and in the openings of the pressure regulator (wrench for brake pipes type 41 08 11 13 f. "Stahlwille", technological plugs).

Disconnect the link 5 of the rear brake pressure regulator drive from the beam 6 of the rear suspension arms (flathead screwdriver, pliers).

Unscrew the bolts 3 fastening the pressure regulator and remove the regulator (interchangeable head 10, extension, ratchet wrench).

Installation

Install the rear brake pressure regulator and secure it with bolts. Bolt tightening torque 12 Nm (1.2 kgf·m) (interchangeable head 10, extension, ratchet wrench, torque wrench).

Remove the plugs from the holes of the regulator and the brake pipes and screw the fittings of the brake pipes into the holes of the rear brake pressure regulator. Tightening torque of fittings 14 Nm (1.4 kgf·m) (wrench for brake pipes type 41 08 11 13 f. "Stahlwille", interchangeable insert 11 type 58 23 10 11 f. "Stahlwille", torque wrench type 50 18 00 04 f. "Stahlwille").

Connect the rear brake pressure regulator link to the rear suspension beam (flathead screwdriver, pliers).

Bleed the brake system.

Rear brake pressure regulator drive adjustment.

Attention. When adjusting the car must be in running order and stand on wheels.

Adjust the rear brake pressure regulator, for which:

• unscrew the coupling bolt 2, Figure 16-2, of the adjusting clutch;
• install the adjusting clutch 3 of the drive lever so that it touches the lever 4 of the rear brake pressure regulator;
• tighten the pinch bolt. Bolt tightening torque 12 Nm (1.2 kgf·m) (interchangeable head 10, ratchet wrench, torque wrench).

Attention. When adjusting, it is not allowed to influence the nut 6 of the regulator rod.

Checking the rear brake pressure regulator

Attention. The rear brake pressure regulator is checked with the vehicle on wheels, with one person on board and a full tank of fuel.

The pressure reading is made diagonally by comparing the rear brake pressure with the set front brake pressure.

If none of the rear brakes are at correct pressure, replace the rear brake pressure regulator.

Attention. Be sure to check both brake circuits. Right front / left rear wheel and left front / right rear wheel.

Remove the protective caps, unscrew the brake bleeders from the right front and left rear brake mechanisms and connect pressure gauges to them (wrench 7, two pressure gauges type Fre. 1085-01).

Bleed the brake system through the bleed fittings on the pressure gauges.

Start the engine.

Press and hold the brake pedal in a position corresponding to the pressure in the front brake cylinder of 100 bar.

Record the readings of the pressure gauge connected to the working cylinder of the rear brake.

Repeat the operation on the other brake circuit.

If the pressure values exceed the allowable values specified in tables 16-1 and 16-2, the rear brake pressure regulator must be replaced. Regulator repair is not provided.

Attention. The pressure difference in the working cylinders of the rear brakes must not exceed 4 bar, regardless of the load on the rear axle.

Reference pressure values in the rear wheel cylinders

Reference pressure values are given in tables 16-1 and 16-2.

Table 16-1 - Excluding axle load distribution (the pressure test is performed with a full fuel tank)

Model car	Pressure in the rear wheel cylinder, bar Modification E0/E1		Pressure in the rear wheel cylinder, bar Modification E2
	K7M engine	K4M engine	K7M engine	K4M engine
R90	37,50...48,40	29,50...40,40	37,00...47,90	28,80...39,90

Table 16-2 - Considering axle load distribution

Automobile model	Pressure in the rear wheel cylinder, bar (with a rear axle load of 700 kg)		Pressure in the rear wheel cylinder, bar (with a rear axle load of 825 kg
	K7M engine	K4M engine	K7M engine	K4M engine
F90	50,68...61,88	Measurement is not performed	64,20...75,40	Measurement is not performed
R90/5 - local	50,68...61,88	42,24...53,44	64,20...75,40	57,20...68,30
R90/7 - local	48,92...60,12	40,90...52,10	59,90...71,10	52,40...63,60

Bleed the brake system and, if necessary, the clutch hydraulic drive (see here).

Check the efficiency of the service brake system.