Wheel cylinders
Disassemble the wheel cylinders, for which remove the protective caps 1 (pic. 6-20) and pistons 2, remove seals 3, support cups 5 and spring 7. Then unscrew fitting 6. Check the cleanliness of the working surfaces of the cylinder and pistons. Surfaces must be perfectly smooth and free of roughness to prevent fluid leakage and premature wear of seals and pistons. Eliminate defects on the cylinder mirror by lapping or grinding. However, an increase in the inner diameter of the cylinder is not allowed.
Pic. 6-20. Wheel Cylinder Details: 1 - protective cap; 2 - piston; 3 - sealant; 4 - body of the wheel cylinder; 5 - spring cups; 6 - air outlet fitting; 7 - spring
Replace seals with 3 new ones. Check the condition of the protective caps 1 and replace them if necessary.
Check the condition of the spring 7. Its length in the free state should be 34 mm, under load 34.3±1.96 N (3.5±0.2 kgf) - 17.8 mm, replace if necessary.
Lubricate all parts liberally with brake fluid before assembling. Install the parts in the reverse order of disassembly. After assembly, check the movement of the pistons, which should be smooth, without jamming.
Pads
Carefully check the pads for damage or deformation.
Check the elasticity of the coupling springs, both upper and lower; replace them if necessary.
Springs should not have residual deformations when stretched: lower - with a force of 343 N (35 kgf), upper - 412 N (42 kgf).
Check the cleanliness of the linings, if dirt or traces of grease are found, carefully clean the linings with a wire brush and rinse with mineral spirits, in addition, check if there is any leakage of grease or oil inside the drum; troubleshoot.
Replace the pads with new ones if the thickness of the pads has become less than 1.5-2 mm.
Brake drums
Examine them. If there are deep grooves or excessive ovality on the working surface, bore the drums on the machine.
Then, on a lathe, grind the drums with abrasive fine-grained bars. This increases the durability of the linings and improves braking uniformity and efficiency.
The largest allowable increase in the nominal diameter of the drum (250 mm) after boring and grinding 1 mm. This tolerance must be strictly adhered to. otherwise, the strength of the drum is violated, as well as the effectiveness of braking.
Checking the wheel cylinders of the rear brakes on the stand.
Install the cylinder on the stand, connect the pipeline from the pressure gauges to it (pic. 6-21) and pump the system.
Pic. 6-21. Scheme for checking the wheel cylinders of the rear brakes: 1 - piston stops; 2 - tested cylinder; 3 - cylinder bracket; 4 - low pressure gauge; 5 - high pressure gauge; 6 - cylinder for creating pressure; 7 - vessel; 8 - flywheel
Adjust stops 1 so that the pistons of the wheel cylinder rest against them.
Check for fluid leakage. Connect a low pressure gauge; slowly turning the flywheel for controlling the drive cylinder, set the fluid pressure to 0.05 MPa (0.5 kgf/cm2).
Ensure that the set pressure is maintained for 5 minutes. Repeat the same test at a pressure of 0.1-0.2-0.3-0.4-0.5 MPa (1-2-3-4-5 kgf/cm2).
Reduce pressure and connect a high pressure gauge. Following these rules, repeat the test at a pressure of 5-10-15 MPa (50-100- 15G kgf/cm2).
Pressure reduction due to liquid leakage through sealing elements, pipeline connections, liquid pumping fittings or through the pores of the casting is not allowed.
Minor (no more than 0.5 MPa (5 kgf/cm2) within 5 minutes) reduction in pressure, especially at higher pressures, due to shrinkage of seals.