The friction lining of the drum surface, as well as the bushings and necks of the expanding fists and the axles of the shoes are subject to the greatest wear in service brakes
Disassembly of the front wheel brake is given in the article "Repair of the front axle and steering rods MAZ".
The thickness of the overlays must be at least 7 mm with a margin of overlays of 1 mm to the control shoulder or rivet head. Cracks, chipping and chips are not allowed on the lining surface.
Installing new pads and riveting them to the pads, use a special device that ensures a snug fit of the pad to the surface of the pad.
The local gap between the block and the lining should not be more than 0.1 mm.
The shape of the rivet, its dimensions, as well as the dimensions of the hole for the rivet in the overlay are shown in fig. 1.
Riveting is carried out from the block side, and the head of the rivet must lie on the mandrel, which ensures that the head retains its shape during the riveting process.
Riveting can be done in a vise with a simple tool.
After riveting the pads, the pads assembled with the pads must be machined in pairs along the outer diameter to the nominal size, if the drum was not bored to the repair size.
If the drum was bored to one of the repair sizes, then the complete blocks with overlays must be machined to the same repair size number (see table).
The pads are processed on a lathe using a special machine that ensures the correct positioning of a pair of pads.
On vehicles equipped with ABS, the lining must be processed on the front axle or rear (middle) axle using a machine model F - 306 from HUNGER (Germany) or similar.
The processing scheme is shown in fig. 2 and 3. The bases for processing are surfaces A and B of the wheel hub flange or hub trunnion.
Before reworking the brakes, the runout of the base surfaces relative to the axis of rotation must be checked. Allowable runouts:
- - surface "A" - 0.2 mm;
- - surface "B" - 0.1 mm.
If the runout of the base surfaces of the hub exceeds the allowable value, the hub must be replaced.
The order of processing overlays is as follows:
- - fix the adjusting lever motionlessly at a distance Г = 90 mm from the mating plane of the brake chamber mounting bracket using a tool;
- - by rotating the hexagon of the worm shaft of the adjusting lever, set the dimension "D" between the centers of the axes of the rollers of the brake pads, equal to 95 + 1.0 mm (Fig. 3);
- - install and fix the centering flange of the processing machine on the wheel hub flange, based on surfaces A and B.
When using the wheel hub trunnion as a base, install and fix the centering coupling of the machine on the trunnion;
- —process brake pads.
It is not allowed to install brake pads with linings of different materials in one brake mechanism (on one axle, on one axle).
The wear of the expanding knuckle necks is allowed up to a diameter of 39.75 mm, the expanding knuckle bushings - up to a diameter of 40.10 mm.
When these surfaces are worn over the indicated necks, they are welded and machined to a nominal diameter (40-0.75) mm, and the bushings are replaced with new ones.
Wear of the support journals of the axes of the pads is allowed up to a diameter of 31.88 mm.
Assemble the service brake in reverse order. When installing the pads, lubricate the axles with Litol-24 grease.
After installing the brake drum on the car, it is necessary to check its runout relative to the axis of rotation, which should not exceed 0.2 mm.
If the runout exceeds the specified value, the brake drum must be replaced.
When installing the adjusting lever, lubricate the splines of the expanding fist with Litol-24 or USSA grease.
On 4WD vehicles equipped with a transmission parking brake, the brake pads are also subject to wear.
The requirements for their condition are the same as for service brake linings.
The differences are that the drum has a diameter of 300 + 0.15 mm, the pads have a width of 100-1.0 mm and they processtsya in diameter 300-0.2 mm.
The shape of the rivet, its dimensions, as well as the dimensions for the rivet in the overlay are shown in fig. 4.
After machining, the brake drum is statically balanced at the factory. Permissible imbalance - no more than 50 gcm.
The holes are drilled on the drum flange with a depth of no more than 6 mm with a minimum pitch of 20 mm.
|
Наименование размера |
Internal diameter brake drum, mm |
Outer diameter block brakes by overlays, mm |
|---|---|---|
|
Rated |
420+0.75 |
420-0.57 |
|
First repair |
421+0.75 |
421-0.57 |
|
Second repair |
422+0.75 |
422-0.57 |
|
Third repair |
423+0.75 |
423-0.57 |