Service brakes are disassembled during maintenance and troubleshooting (oiling, wear and tear of brake pad linings, wear or damage to wheel cylinder seals, breakage of return spring, etc.)
Removing and disassembling service brake parts
Remove the wheel and hub assembly with the brake drum, clean the brake mechanism from dirt and rinse.
Using the mounting spatula as a lever, disconnect the return spring 2.
Remove retaining clips 9, pads 8 and brake pads 6 from the axles 11 of the pads.
Disconnect the brake fluid supply pipeline from the wheel cylinder 1, unscrew the bolts securing it to the shield and remove the cylinder assembly.
If necessary, loosen the screws and remove the brake shield.
If the shoe linings or the shoe assembly cannot be replaced, then it is not recommended to unscrew the nuts 12 and rotate the axles 11 in the shield bracket, which will allow the shoes to take their previous position relative to the brake drum during assembly, and, therefore, will facilitate the adjustment of the gaps between the shoe linings and brake drum.
When disassembling the wheel cylinder, remove the cap springs 1 (fig. 3), caps 2 .assembly with pistons 4.
Remove cuffs 5, cuff holders 6 and spring 9.
After dismantling, wash the wheel cylinder parts in alcohol or brake fluid, and the parts of the mechanical part of the brake in unleaded gasoline.
Washed parts should be carefully inspected and measured if necessary.
If the depth of sinking of the heads of the rivets fastening the linings is 0.5 mm or less, then the linings should be replaced with new ones.
Pistons, cuffs and cylinders in the presence of scratches or significant wear of the working surfaces must also be replaced with new ones.
The protective caps of the cylinders should be especially carefully examined, since the durability and reliability of the operation of the wheel cylinder as a whole depend on their condition.
In case of through breaks and cracks, the cap must be replaced using a tool (Fig. 4).
Dimensions for checking the main parts of the service brake are shown in table 1.
|
Detail |
Size, mm |
|
|---|---|---|
|
Value |
valid |
|
|
Support bracket brake shoes Hole Diameter under shoe axles |
22+0.045 |
22,10 |
|
Brake Pad Axis Neck outside diameter under pad bushing |
28-0.025 |
27.85 |
|
Wheel Cylinder Hole diameter for piston |
35+0.027 |
35.06 |
|
Piston wheel cylinder Outside Diameter |
35-0.075 |
34.85 |
|
Brake shoe assembly Inner diameter of bushing |
28+0.033 |
28,10 |
|
Brake drum Drum inner diameter |
420+0,380 |
424,40 |
In case of significant wear and the presence of annular grooves on the working surface of the brake drum, grind it, as well as the pads assembled with linings, to one of the repair sizes indicated in Table 2.
|
Repair dimensions |
Inner diameter brake drum, mm |
Outer pad diameter overlays 2Rmm |
|---|---|---|
|
Value |
420+0.38 |
420-0.60 |
|
First |
421+0.38 |
421-0.60 |
|
Second |
422+0.38 |
422-0.60 |
|
Third |
423+0.38 |
423-0.60 |
When turning, base the brake drum on the inner surfaces of the outer rings of the hub bearings, and the shoes as shown in fig. 5.
To assemble the wheel brake in the reverse order of disassembly, it is necessary to fulfill a number of the following mandatory requirements:
- the mirror of the wheel cylinder, the piston and the sealing collar should be lubricated with brake fluid. Apply graphite lubricant to the pad bushings.
Before connecting the wheel cylinders to the vehicle's hydraulic system, replace the brake fluid, clean the fluid reservoir on the pneumatic boosters from sludge.
Before installing the hub with the brake drum, bring the pads inward with adjusting eccentrics 4 (Fig. 2) and setting the axes of the pads to the position when in which the installation risks at the ends of the axles are directed back at the axis of the front pad, and forward at the axis of the rear.
If, during disassembly, the position of the axes of the shoes on the brake shield is not disturbed, and during assembly, the shoes are installed in their places, then the gaps between the shoes and the brake drum should be adjusted only with eccentrics 4, turning them (see Fig. 2) until the wheel will not brake.
Then turn the eccentric in the opposite direction until the wheel rotates freely (turn the wheel in the direction of the adjustable shoe).
After adjustment, check the gap through the hatch in the brake drum with a feeler gauge 200 mm long at a distance of 30 mm from the edges of the lining.
The gaps should be at the toe (upper part of the last) 0.35 mm, at the heel (lower part of the last) 0.20 mm.
After replacing the brake pads or installing other complete pads, as well as in case of violation of the position of the axes of the pads on the shields, the gaps should be adjusted using eccentrics 4 and axles 11 of the pads.
In this case, turn the eccentric 4 to slow down the rotation of the wheel.
Turning the axle 11 of the block, determine the direction of its rotation, in which the wheel will rotate freely.
Continue rotation of the block axle in the same direction until the wheel is completely braked.
Divide the angle of rotation of the axle of the shoe from the first braked state of the wheel to the second in half and set the axle in this position.
Repeat this operation several times. Each time, the angle of rotation of the block axle from the first braked state of the wheel to the second will decrease.
After completing the adjustment, make a gap of 0.20 mm at the heel of the shoe, for which insert a probe of 0.20 mm between the drum and the heel of the shoe and slightly clamp it by turning the axis of the shoe.
In this case, the gap at the toe of the shoe should be 0.35 mm. If the gap at the toe of the pad is different, the adjustment should be continued.
After adjusting the brakes of all wheels, install the axle shafts and bleed (fill) the hydraulic system with brake fluid, having previously thoroughly cleaned the outer surfaces of the main brake cylinders, brake fluid reservoirs and bypass valves from dirt.
Fill the system with liquid and bleed the brakes only if there is air (7.5 kgf/cm2) in the car's pneumatic system.
Before filling, carefully remove dirt from the main cylinders and tanks.
Then, having removed the sealing tubes 1 from both cylinders (Fig. 6) and unscrewing the filler plugs 2, fill the reservoirs with brake fluid.
Bleed air from the master cylinders through bypass valve 3.
The procedure for bleeding the main cylinders and service brake cylinders:
Remove the rubber cap from the bypass valve 3 (Fig. 6), put on it the tube provided in the tool kit (Fig. 6), lower its open end into brake fluid poured into a glass vessel with a capacity of at least 0.2 l;
Unscrew the bypass valve ½ - ¾ turn, then depress the brake pedal several times.
Press quickly and release slowly. Repeat pressing until no more air bubbles come out of the tube.
During the pumping process, it is necessary to add liquid to the tanks, avoiding a “dry bottom”, since air will again enter the system.
While pressing the pedal, tighten the bypass valve of the cylinder tightly, remove the tube and put on the cap.
In the same way, bleed the wheel brake cylinders through the bypass valve (fig. 6) in the following sequence (fig. 6):
I - middle left, II - back left, III - back right, IV - middle right, V - front right, VI - front left.
After pumping all the cylinders, add fluid to the tanks to a level of 15...20 mm below the upper edge of the filler neck, tighten the filler plug tightly, attach the sealing tube.
When changing the brake fluid, disassemble the wheel and master cylinders, wash the working surfaces of the parts.
When assembling the wheel cylinders, lubricate the piston and the inner surface of the cylinders with castor oil.