The parking brake is a drum-type brake with mechanical actuation (Fig. 1).
The parking brake actuation, through a lever and rod, is connected to the lever 13 of the brake valve, which ensures that when braking the vehicle with the parking brake, the service brake system of the trailer (semi-trailer) is activated.
The parking brake is mounted on the transfer case.
The brake shield with the shoes is fixed to the bearing cover of the rear axle drive shaft, and the brake drum is fixed to the flange of this shaft.
The parking brake and its actuation are partially or completely disassembled mainly when braking efficiency decreases and cannot be eliminated by adjusting the actuation, as well as when the reliability of locking the parking brake lever in the braked state decreases.
The causes of decreased braking efficiency may be oiling, heat-induced destruction or complete wear of the brake shoe linings, as well as loosening of the bolts securing the brake shield to the transfer case.
The cause of the lever locking malfunction is wear of the sector 5 or the pawl 4 of the lever.
Disassembly and removal of parking brake parts
Unscrew the nuts and remove the driveshaft of the middle axle drive.
Unscrew the nut and remove the bolt securing the ejection tube to the third frame cross member.
Unscrew the two screws securing the drum to the flange, lift the ejection tube upwards and remove the drum.
Remove the tension springs 24 and the shoes 23.
Remove the split pins and remove the pin, disconnect the rod 20 from the lever 21.
Remove the split pins and unscrew the flange securing nut, press the flange off the rear axle drive shaft of the transfer case.
Unscrew the bolts and remove the oil deflector, gasket and brake shield as an assembly.
Unscrew the bolt 25 and remove the adjusting lever 21.
Remove the retaining ring and extract the expansion cam 22.
If necessary, press out the expansion cam bush from the shield bracket. (It is not recommended to press out the shoe axle from the lower bracket of the shield).
Disassembly and removal of parking brake actuation parts
Remove the split pins and remove the pin connecting the rod 10 to the lever 6.
Unscrew the four bolts 8 in the cab and remove the bracket as an assembly.
Remove the split pins and remove the pins connecting the rod 18 to the levers 11 and 19, the rod 15 to the levers 13 and 17, and the rod 10 to the lever 17.
Remove the split pins from the lever 19 axle, remove the washer and the lever.
Unscrew the four bolts and remove the bracket 16 with the levers as an assembly.
Disassemble the bracket 7, for this purpose unscrew the bolt securing the lever 3 on the shaft 9 and remove the lever with the pawl 4, lever 2 and pawl rod 1 as an assembly.
Remove the key of the lever 3 from the shaft 9.
Unscrew the flange securing bolts and the bolt securing the lever 6 on the shaft 9, remove the flange.
Press out the shaft 9 with the key as an assembly from the lever 6 and from the bracket through the hole for the flange.
Remove the key of the lever 6 from the shaft 9. If necessary, unscrew the two bolts and remove the sector 5.
Press out the bushes from the bracket 7 and the flange.
Unscrew the bolt and remove the lever 11 from the shaft and its key.
Extract from the bracket 16 the shaft with the lever 17 as an assembly, which is pressed onto the splined end of the shaft.
It is not recommended to separate the splined end of the shaft from the lever 17. If necessary, press out the bushes from the bracket 16.
The dimensions for checking the main parts are given in Table 1.
Table 1. Dimensions for checking hand brake parts
Hand brake shoe axle. Outer diameter at the shoe support point:
- - nominal size - 28.15+0.100 mm;
- - permissible size - 28.10 mm
Expansion cam bush. Inner diameter:
- - nominal size - 25+0.150 mm;
- - permissible size - 26.00 mm
Expansion cam. Diameter of the journal for the bush:
- - nominal size - 25-0.025 mm;
- - permissible size - 24.85 mm
Parking brake lever shaft. Outer diameter:
- - nominal size - 20-0.080 mm;
- - permissible size - 19.80 mm
Clutch pedal shaft bush. Inner diameter:
- - nominal size - 20+0.150 mm;
- - permissible size - 21.00 mm
Bush. Inner diameter:
- - nominal size - 20.45+0.100 mm;
- - permissible size - 21.00 mm
Intermediate shaft. Outer diameter for the bush:
- - nominal size - 20-0.025 mm;
- - permissible size - 19.80 mm
Brake drum. Inner diameter:
- - nominal size - 300+0.34 mm;
- - permissible size - 303.34 mm
Worn linings should be replaced if less than 0.5 mm remains from their surface to the rivet heads.
In case of significant and uneven (with annular grooves) wear of the brake drum working surface, the drum, as well as the shoes with their linings, must be machined to repair dimensions (Table 2).
Table 2. Repair dimensions
Brake drum inner diameter:
- Nominal size - 300+0.34 mm;
- First repair - 301+0.34 mm;
- Second repair - 302+0.34 mm;
- Third repair - 303+0.34 mm
Shoe outer diameter at the linings:
- Nominal size - 300-0.25 mm;
- First repair - 301-0.25 mm;
- Second repair - 302-0.25 mm;
- Third repair - 303-0.25 mm
When turning on a machine, the shoes should be positioned as shown in Fig. 3. Plates 1 mm thick should be installed between the expansion cam and the shoe tappets.
Oiled linings must be washed with unleaded petrol and then dried.
Linings that have a loose composition and peeling on the working surface due to overheating must be replaced.
Cracks and other damage to the shoes are not allowed. If the tappets become loose on the shoe ends, the screws should be tightened.
Assemble the parking brake and its actuation in the reverse order of disassembly. The following requirements must be observed:
- - when installing the brake shield on the transfer case, the oil deflector gasket must be lubricated with sealing lubricant (the tightening torque of the shield mounting bolts should be 8.0–10 kgf·m);
- - lubricate the expansion cam and its bush, the shoe axle and the brake shoes at the point of support on the axle, as well as the axles and bushes in the parking brake actuation, with graphite grease;
- - when installing the tension springs 24 (see Fig. 1), install the spring with a diameter of 28 mm at the expansion cam, and the spring with a diameter of 20 mm at the shoe support axle;
- - align the marks «a» on the splined ends of the expansion cam 22 and the adjusting lever 21 during assembly;
- - install the lever 6 with its machined side facing the right inner wall of the bracket 7.
After assembly, the parking brake must be adjusted. The lever 2 must be in the lowest extreme position on the stop.
In the connection of the clamp 12 with the lever 13 of the brake valve, a clearance of up to 2 mm must be set by changing the length of the rod 15.
By changing the length of the rod 18 and repositioning the lever 21 on the splines of the expansion cam 22, adjust the clearance between the brake shoe linings and the drum, which should be within 0.3–0.6 mm.
When the parking brake is correctly adjusted, the travel of the lever 3 during full braking should be four to six teeth of the sector, and the actuation lever must be locked.
After the brake shoe linings have bedded in, the efficiency of the parking brake should be checked.