6.7. Brake mechanism of a back wheel

Description of the device

Fig. 6.5. Brake mechanism of a back wheel: 1 – front brake shoe; 2 – ottyazhny spring of an expansion level; 3 – the spring is clamping; 4 – the level is expansion; 5 – the spring is coupling top; 6 – the cylinder is wheel; 7 – axis of the razzhimny lever; 8 – plug; 9 – board of a back brake; 10 – lever of razzhimny; 11 – back brake shoe; 12 – tip of a cable of the drive of the parking brake; 13 – spring; 14 – the spring is coupling lower


Brake mechanisms of back wheels are equipped with the self-established blocks (floating type). Brake shoes 1 and 11 (fig. 6.5) are put in action by one hydraulic wheel cylinder 6 with two pistons. The steel spring cutting rings connected to pistons and which are carrying out a role of the automatic device supporting a constant gap between a frictional overlay and the working surface of the reel are inserted into hydraulic cylinders with a tightness. In the brake drums cast from aluminum alloy pig-iron sleeves are filled in.

Replacement of brake shoes
Minimum admissible thickness of frictional overlays of brake shoes of 1,5 mm. At wear of slips to this thickness, their fragile connection with the basis, oiling of surfaces of slips or in the presence on overlays of deep furrows and chips replace brake shoes new at the same time on both brake mechanisms of forward wheels, i.e. both couples.
If blocks do not be replaced, at removal mark them that at assembly to put on former places as rings of automatic devices were established on a certain block, and for other block the piston should be shifted in a starting position again. Each excess movement of a ring, hit of dirt or application of improper mandrels can lead to emergence longitudinal рисок on a mirror of the cylinder and a leak of brake fluid.
1. Remove a wheel and the brake drum.
2. Remove top 5 and lower the 14th coupling springs of blocks by means of special pincers.
3. Remove an ottyazhny spring of an expansion level.
4. Raise a pad of a clamping spring 3 and take out a front brake shoe 1.
5. Remove an expansion level 4.
6. Having raised a pad of a clamping spring, take out a front brake shoe 1 and, having wrung out a spring, disconnect a tip of a cable of the drive of the parking brake from the razzhimny lever.
7. Turn off a nut of an axis of the razzhimny lever, take out the plug and disconnect razzhimny the lever from a back block.
8. Establish brake shoes upside-down. At installation of new blocks press pistons into the case of the wheel cylinder against the stop one in another with identical distance from case end faces. Do it by easy blows of the hammer through a wooden drift.

Repair of the brake drum
1. Remove a wheel and clear the brake drum of dirt.
2. Be convinced of free rotation of the brake drum. The lever of the parking brake at the same time has to be lowered.

Fig. 6.6. Installation of hairpins in openings


3. Turn out two directing hairpins of fastening of a drum to a nave, establish hairpins in carving openings And (fig. 6.6) of a flange of a drum and, screwing them, remove a drum. At strong corrosion of a flange of a drum and a nave moisten places of their contact with liquid of the WD-40 type and sustain some time. In order to avoid damage of the reel 4 and deformation of a board of a brake do not beat with the hammer a rim of a drum and you do not enter the screw-driver between a board and a rim of a drum, using it as the lever.

Fig. 6.7. Moving of a front brake shoe: 1 – bolts of fastening of a wheel; 2 – lever (assembly shovel); 3 – core


4. At considerable wear of a drum on its working surface the ring ledge interfering removal of a drum is formed. In this case through a big opening in a flange of a drum insert a core of 8 mm (

Fig. 6.8. Moving of a back brake shoe: 1 – face key; 2 – bolts of fastening of a wheel; 3 – lever (assembly shovel); 4 – brake drum; 5 – the directing hairpin; And – an opening with a carving

fig. 6.7) in an opening of a sock of a forward block. A neck or an assembly shovel, leaning on bolts of fastening of a wheel, turn the brake drum towards the wheel cylinder so that the block moved, having shifted at the same time a ring of automatic adjustment of a gap in the wheel cylinder. Shift a back brake shoe, having put on a face key of 1 (fig. 6.8) a nut of an axis of the razzhimny lever, and remove the brake drum (in case of need use the methods described above).
5. Maximum permissible diameter of a working surface of the reel of 231,6 mm. Examine the internal working surface (mirror) of the removed reel and check its ovality. The difference of the measured diameters (maximum and minimum) should not be more than 0,2 mm. In the presence of deep risok or the increased ovality the drum can be chiseled, basing on the central opening and pressing an internal surface of a flange of a drum to adaptation. For rigidity preservation it is impossible to chisel drums more than on 0,8 mm on the party. After boring the working surface of the reel has to have a roughness no more than 1,6 microns.
6. Before installation of the brake drum carefully clear its privalochny surfaces, basic openings and privalochny surfaces of a flange of a half shaft of dirt, corrosion or забоин and slightly grease with refractory and moisture resistant lubricant.
7. The brake drum has to be put on densely against the stop a half shaft flange only by effort of a hand. Thus after installation the drum should not move to half shafts freely.

Repair of wheel cylinders
1. Lift the relevant party of the car a jack, put a support under a jack nest, remove a jack and remove a wheel and the brake drum.
2. Remove both coupling springs of blocks and an ottyazhny spring of an expansion level by means of special pincers and, having moved apart blocks, bring their ends out of cuts of basic cores of pistons.
3. Disconnect the pipeline from the wheel cylinder. Muffle a pipeline opening.
4. Turn off two bolts of fastening of the wheel cylinder to a brake board and remove the cylinder.
5. Remove protective rubber covers from the wheel cylinder.
6. The screw-driver inserted into grooves of basic cores of pistons turn pistons on 90 ° and take out them from a cylinder cavity.
7. Carefully wash out an internal cavity of the wheel cylinder fresh brake fluid.

Fig. 6.9. The device for extraction of a spring ring of the automatic device from the wheel cylinder


8. Take out from a cylinder cavity both spring rings of the automatic device by means of a special stripper (fig. 6.9).
9. Remove sealing rubber cuffs from pistons.
10. Turn out the valve of production of air from the cylinder.
11. Carefully wash out details of the disassembled brake cylinder, examine and establish their suitability to further work.
12. Replace wheel cylinders assembled if on their working surface there are deep longitudinal risks or other defects leading to a leak of brake fluid. Grinding of their working surface is not allowed as at the same time the tightness in the cylinder of a spring ring of the automatic device for maintenance of a gap between a block and a drum decreases and their working capacity is broken.
13. Irrespective of a state replace sealing rubber cuffs.
14. Before assembly carefully wash out all details in fresh brake fluid.
15. Grease before assembly by fresh brake fluid of a cuff, pistons, rings and the internal surface of the cylinder.
16. Put on cuff pistons so that they were turned by the parties of bigger diameter in the cylinder.

Fig. 6.10. Installation of a spring ring of the automatic device in the wheel cylinder: and – compression of a ring in special pincers; – installation of a ring in a mandrel; in – installation of a ring in the wheel cylinder; 1 – special pincers; 2 – ring; 3 – mandrel; 4 – wheel cylinder


17. Squeeze rings in special pincers and insert into a mandrel for installation of a ring in the cylinder (fig. 6.10). Enter a ring with a mandrel into a cylinder cavity so that the section of a ring was parallel to the privalochny plane of the cylinder and was in its top part. Then finish a mandrel against the stop of its fillet in a cylinder end face, press the handle of a mandrel and push out from it a ring. Take out a mandrel from the cylinder.
18. Insert the piston into the cylinder against the stop in a ring, accurately filling a cuff edge, and turn it on 90 °. The cut of a basic pin of the piston has to be parallel to the privalochny plane of the cylinder at the same time.
19. In the absence of special devices for assembly of wheel cylinders insert pistons against the stop into rings and press them on a manual press or easy blows of the hammer through a wooden drift against the stop one in another with their identical distance to end faces of cylinders. The cut of a basic core of the piston has to be parallel to the privalochny surface of the cylinder. In order to avoid education at the same time longitudinal рисок on a mirror of the cylinder examine a ring before a press fitting and if necessary polish all zaboina on a cylindrical surface and edges. Carefully clear a ring and the cylinder of the smallest grains of sand.
20. Put on rubber protective covers and screw the valve of production of air. After installation and fastening of the cylinder in the brake mechanism of a wheel, assembly of blocks with springs and installations to the place of the brake drum pump over the brake system and be convinced of free rotation of the drum at the released brake pedal.