Mechanically operated drum-type parking brake (fig. 1)
The parking brake drive is connected by a lever and a rod to the lever 13 of the brake valve, which ensures that the working brake system of the trailer (semi-trailer) is activated when the car is braked with the parking brake.
The parking brake is mounted on the transfer case.
The brake shield with pads is fixed to the bearing cap of the rear axle drive shaft, and the brake drum is on the flange of this shaft.
The parking brake and its drive are partially or completely disassembled, mainly when the braking efficiency is reduced, which cannot be eliminated by adjusting the drive, as well as when the reliability of fixing the parking brake lever in the braked state is reduced.
The reasons for the decrease in braking efficiency may be oiling, destruction from heating or complete wear of the linings of the brake pads, as well as loosening of the bolts securing the brake shield to the transfer case.
The reason for the violation of the fixation of the lever is the wear of sector 5 or pawls 4 of the lever.
Disassembly and removal of parking brake parts
Remove the nuts and remove the driveshaft of the middle axle drive.
Unscrew the nut and remove the bolt securing the ejection pipe to the third cross member of the frame.
Unscrew the two screws securing the drum to the flange, lift the ejection pipe up and remove the drum.
Remove the return springs 24 and pads 23.
Unpin and remove the pin, disconnect the rod 20 from the lever 21.
Unpin and unscrew the flange fastening nut, press the flange off the rear axle drive shaft of the transfer case.
Remove the bolts and remove the oil separator, gasket and brake shield assembly.
Unscrew bolt 25 and remove adjusting lever 21.
Remove the retaining ring and extract the expander knuckle 22.
If necessary, press the expander bushing out of the shield bracket. (It is not recommended to press the axle of the pads out of the bottom bracket of the shield).
Disassembly and removal of parts of the parking brake drive
Unpin and remove the pin connecting the rod 10 with the lever 6.
Unscrew four bolts 8 in the cab and remove the bracket assembly.
Unpin and remove the pins connecting rod 18 with levers 11 and 19, rod 15 with levers 13 and 17, rod 10 with lever 17.
Unpin the lever axle 19, remove the washer and the lever.
Remove four bolts and remove bracket 16 complete with levers.
Disassemble the bracket 7, to do this, unscrew the bolt securing the lever 3 on the shaft 9 and remove the lever assembly with pawl 4, lever 2 and pawl 1.
Remove the key of lever 3 from shaft 9.
Unscrew the flange mounting bolts and the lever mounting bolt 6 on the shaft 9, remove the flange.
Press the shaft 9 complete with the key out of the lever 6 and out of 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 bushings out of bracket 7 and flange.
Remove the bolt and remove lever 11 from the shaft and its key.
Remove from the bracket 16 the shaft assembly with the lever 17, which is pressed onto the splined end of the shaft.
It is not recommended to disconnect the splined end of the shaft from the lever 17. If necessary, press bushings 16 out of the bracket.
Dimensions to control the main parts are shown in Table 1.
|
Detail |
Dimensions, mm |
|
|---|---|---|
|
Denomination |
valid |
|
|
Handbrake shoe axle Outer diameter at pad support |
28.15+0.100 |
28.10 |
|
Spreader bushing Inner diameter |
25+0.150 |
26.00 |
|
Expanding knuckle Neck diameter for bushing |
25-0.025 |
24.85 |
|
Parking lever shaft Outer diameter |
20-0.080 |
19.80 |
|
Clutch pedal shaft bushing Inner diameter |
20+0.150 |
21.00 |
|
Sleeve Inner diameter |
20.45+0.100 |
21.00 |
|
Intermediate shaft Outer diameter for bushing |
20-0.025 |
19.80 |
|
Brake drum Inner diameter |
300+0.34 |
303,34 |
Worn pads, if there is less than 0.5 mm left from their surface to the rivet heads, should be replaced.
In case of significant and uneven (with annular grooves) wear near the working surface of the brake drum, it, as well as the pads assembled with linings, must be machined to repair dimensions (Table 2).
|
Rem. Size |
Int. diameter brake drum, mm |
External dia. block by overlays |
|---|---|---|
|
Denomination |
300+0.34 |
300-0.25 |
|
First |
301+0.34 |
301-0.25 |
|
Second |
302+0.34 |
302-0.25 |
|
Third |
303+0.34 |
303-0.25 |
When turning on the machine, the pads should be based, as shown in fig. 3. At the same time, install plates 1 mm thick between the expanding fist and crackers of the blocks.
Oiled brake pads should be washed with unleaded gasoline and then dried.
Pads that have a loose composition on the working surface and peel off due to overheating must be replaced.
Cracks and other damage to pads are not allowed. If the fastening of the crackers to the toes of the shoes is loosened, the screws should be tightened.
Assembly of the parking brake and its drive in the reverse order of disassembly. In this case, the following requirements must be met:
- - when installing the brake shield on the transfer case, the oil catcher gasket must be lubricated with sealing lubricant (the tightening torque of the shield fastening bolts must be 8.0-10 kgf / m);
- - the expanding fist and its bushing, the axle of the pads and the brake pads in the place of support on the axle, as well as the axles and bushings in the parking brake drive, lubricate with graphite grease;
- - when installing coupling springs 24 (see Fig. 1), install a spring with a diameter of 28 mm at the expanding fist, and with a diameter of 20 mm - at the axis of the shoe support;
- - labels "a" on the splined ends of the expanding fist 22 and the adjusting lever 21 during assembly;
- - install the lever 6 with the processed side to the right inner wall of the bracket 7.
The parking brake must be adjusted after assembly. In this case, lever 2 should be in the lowest position on the stop.
In the connection of the bracket 12 with the lever 13 of the brake valve, be sure to set a gap of up to 2 mm by changing the length of the rod 15.
By changing the length of the rod 18 and shifting the lever 21 on the splines of the expanding fist 22, adjust the gap between the brake pads and the drum, which should be within 0.3-0.6 mm.
With a properly adjusted parking brake, the stroke of lever 3 at full braking should be four to six teeth of the sector, while the drive lever should be fixed.
After running in the brake pads, check the effectiveness of the parking brake.