The two-section brake valve (Fig. 1) is designed to control the actuating mechanisms of the vehicle's service brake system, as well as to control the valve of the trailer brake actuator.
The brake valve consists of an upper and a lower body.
The lever mechanism of the valve is attached to the upper body. The lever body is protected from dirt and moisture by a boot.
The upper cylinder controls the brakes of the trailer (semi-trailer), the lower cylinder controls the brakes of the tractor.
Figs. 2 to 4 show in detail the construction of the covers of the upper and lower cylinders of the brake valve.
The valve is removed from the vehicle and partially or completely disassembled to eliminate air leakage through the exhaust port due to leakage of valves 15 or seals 13 and 19 (see Fig. 1).
The location of the air leak must be determined before removing the valve from the vehicle according to the following signs:
- - the leak stopped after turning the parking brake lever 4 — the valve 15 of the upper cylinder is leaking;
- - the leak did not stop after turning the parking brake lever — the seal 13 of the upper cylinder piston is leaking;
- - the leak did not stop after depressing the brake pedal — the valve 15 or the seal 19 of the lower cylinder piston is leaking.
The diagram for checking the tightness of seals with pistons is shown in Fig. 5.
The brake valve is mounted on a special bracket under the cab and secured with three bolts on the inside of the left frame side member.
When removing the brake valve, remove the split pins of the rods, disconnect the ends of the actuator rods from the levers 2 and 4 (see Fig. 1) of the brake valve.
Unscrew the union nuts and disconnect the pipelines from the brake valve.
Unscrew the nuts of the valve mounting bolts, remove the washers from the bolts, the brake valve and its bracket.
Valve repair
Defective parts should be replaced during repair with new ones, factory-made.
When assembling the brake valve after repair, tighten the rod nut 1 so that the free travel of the end of lever 2 is 0.2–4.0 mm, and its working travel is 19–21 mm, the free travel of lever 4 is 8–12 mm, and its total travel is 44–47 mm.
After assembly, check the brake valve and, if necessary, adjust it on a special stand at a constant air pressure of 6.00–6.50 kgf/cm².
With levers 2 and 4 in the free position, the air pressure in the pneumatic line of the trailer brakes should be 4.8–5.3 kgf/cm², and in the pneumatic line of the vehicle brakes it should be absent.
Perform adjustment by turning nut 3, after first unscrewing the lock bolt 6.
If the air pressure in the brake line is less than 4.8–5.3 kgf/cm², turn nut 3 clockwise.
When lever 2 is fully retracted, the air pressure in the pneumatic line of the trailer should be absent, and in the pneumatic line of the vehicle brakes it should be equal to the air pressure in the air tank.
Perform adjustment with the rod nut 1 within the working travel of the lever end of 19–21 mm.
The adjustments must be checked at three fixed positions of the mode ring 22, which should be turned with a wrench without jamming.
When lever 4 is fully retracted, the air pressure in the pneumatic line of the vehicle brakes should be absent, and in the pneumatic line of the trailer brakes it should decrease from 4.8–5.3 kgf/cm² to 0.
When the lever returns to its original position, the air pressure in the trailer's pneumatic line should increase to 4.8–5.3 kgf/cm².
If the air pressure in the pneumatic line of the trailer brakes has not dropped to 0, then adjust the valve by turning the guide washer 3 (see Fig. 3) relative to the nut 1, reducing dimension a equal to 97.5 mm.
After adjustment, fix the position of the washer relative to the nut 1 and tube 4 with the retaining ring 2, after drilling a new hole in the nut and tube.
Install the checked and adjusted brake valve on the vehicle, connect the ends of the rods and pipelines.
Check and, if necessary, adjust the brake valve actuator.
The maximum air pressure in the pneumatic system after the brake valve (upper scale of the pressure gauge) is adjusted by the bolt 12 (Fig. 6) that limits the brake pedal travel and should be within 4.0–4.5 kgf/cm².
After adjustment, lock the bolt by tightening the lock nut 11.
Adjust the free play of the brake pedal by changing the length of the rod 16.
It should be within 15–30 mm.
The beginning of the working travel is determined by a significant increase in pedal force.
In the connection of the lever with the rod, the clearance between the pin and the bracket should not exceed 2 mm. Adjust by changing the length of the rod.
The brake valve actuator (see Fig. 6) is structurally combined with the clutch control actuator and consists of a suspended pedal 5, levers 22 and 24, rods 8 and 16.
Removal and disassembly of the clutch and brake valve control actuator
Disconnect and remove springs 1 and 13.
Remove the split pins of the pins and remove rods 8, 9, 16 and 17. Unscrew bolts 7, 19 and remove brackets 10, 21 as assemblies.
When disassembling bracket 10, remove the split pins from the ends of shaft 32 and remove washers 28 and 34.
Unscrew the clamp bolt 31 of lever 26.
Remove clutch pedals 2 and brake pedal 5, key 33 of the clutch pedal.
Move lever 26 towards the clutch pedal side and remove key 30. Remove shaft 32 from the bracket, remove levers 24 and 26.
When disassembling bracket 21, unscrew the clamp bolts 18, remove levers 20 and 23, keys, shaft and lever 22. If necessary, press out the bushings from the levers and brackets.
The data for checking the technical condition of the parts of the brake and clutch actuator are given in the table.
Table 1. Control dimensions of actuator parts
Clutch pedal shaft. Outer diameter:
- - nominal size - 20-0.020 mm;
- - permissible size - 19.50 mm
Clutch pedal shaft bushing. Inner diameter:
- - nominal size - 20+0.150 mm;
- - permissible size - 20.50 mm
Brake pedal bushing. Inner diameter:
- - nominal size - 32+0.150 mm;
- - permissible size - 32.50 mm
Brake pedal shaft. Outer diameter:
- - nominal size - 32-0.100 mm;
- - permissible size - 31.50 mm
Clutch release actuator shaft. Outer diameter:
- - nominal size - 20-0.020 mm;
- - permissible size - 19.50 mm
Brake valve control lever assembly. Diameter of the hole in the bushing for the shaft:
- - nominal size - 20+0.150 mm;
- - permissible size - 20.50 mm
Assemble the brake and clutch control actuator in the reverse order of disassembly.
During assembly, lubricate the bushings and shafts with graphite grease.
Connect the brake pedal shaft and lever 24 according to the marks on the splined ends of these parts.
Determining the free play of the brake pedal
Measure the free play of the brake pedal (Fig. 7). If it is greater or less than 15–25 mm, adjust it by changing the length of the rod 2.
When measuring free play, the actuating lever must be pressed against the stop of the upper brake valve cover. The beginning of the working travel is determined by a significant increase in force.
