In these brakes, both brake shoes are pressed against the brake drum under pressure from the pistons of the wheel cylinder, which is located between the upper parts of both brake shoes. The location of the brake pads in the AUDI 80 brake drum is such that one of the brake pads has a self-reinforcing braking effect, and the wheel cylinder used in this type of brake is dual. The self-reinforcing braking effect consists in the fact that one of the brake pads, when the wheel reaches a certain number of revolutions, begins to independently attract to the brake drum, facilitating the braking process. This block is the front block when viewed in the direction of travel.
The brake drum mechanism is self-aligning. This effect is provided by an adjusting device for automatically adjusting the gap between the brake shoes. As the brake pads wear, the expansion bar spring between both brake pads is forced to lengthen so that the pads lie against the brake drum when braking. This expander bar extension provides a wedge with a return spring that increases in tension as the brake pads wear and moves the wedge to allow the expander bar spring to extend.
When determining the residual thickness of the brake linings, only the thickness of the front pad is measured, because it wears out to a greater extent.
1. Put the rear of the car on jack stands.
2. Remove the plastic cap from the respective rear wheel (see illustration).
3. Shine a flashlight into the viewing hole in the caliper body. The remaining thickness of the brake pads without backing plate must be at least 2.5 mm.
The brake drum can be removed without removing the wheel.
4. Turn out one of bolts of fastening of a wheel.
5. Place the rear of the vehicle on jack stands.
6. Rotate the rim or brake drum until the hole of the removed wheel bolt is at the top.
7. Insert a screwdriver into the bolt hole and push the adjusting wedge up. The brake pads will then move away from the brake drum.
8. Remove the protective cap from the wheel hub nut.
9. Bend the ends of the expansion pin on the nut and remove it.
10. Remove the slotted lock washer and remove the hub hex nut.
11. Remove thrust washer and outer bearing
12. Remove the brake drum (see illustration).
13. Adjust the bearing play after installing the brake drum in place.
14. Squeeze out a brake pedal that brake pads were self-installed in a brake drum.
Attention! If the brake adjustment wedge cannot be pushed up because it is rusty, have an assistant depress the brake pedal. This will move the wedge up. Now the assistant should release the pedal. In this position of the pedal, you can remove the screwdriver from the hole for the wheel bolt. If the screwdriver is removed earlier, the wedge will return to its original position.
Attention! The brake pedal can only be depressed with the brake drums not removed.
Checking the condition of the brake drum
The surface of the brake drum to which the brake pads are attached must be as smooth as possible. If it has grooves or corrugations formed as a result of friction of the rivets of worn out brake linings, then the brake drum can be turned. The new brake drum has an inner diameter of 230 mm. After completion, the inner diameter of the brake drum must not exceed 231 mv 3 otherwise both brake drums must be replaced.
If the drum has been reworked, the brake pads should be fitted with pads of increased thickness.
Wheel cylinder - removal
15. Remove the brake drum.
16. Remove the brake pads.
17. Turn out the pumping union.
18. Disconnect the brake hose. If a new wheel cylinder will not be installed immediately, then press the brake pedal and hold it in this position to avoid leakage and loss of brake fluid.
19. Turn out two bolts of fastening of the wheel cylinder on a support and remove the cylinder.
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