Pipelines and connections
To prevent failure of the brake system, carefully check the connection of all pipelines.
During the inspection, ensure that:
- metal pipes were free of cracks, dents and were located away from sharp edges that could damage them;
- flexible hoses do not come into contact with mineral oils or lubricants that dissolve rubber. Press the brake pedal hard to check whether the hoses develop any bulges that indicate a malfunction;
- all pipe fastening brackets were tightened well. Loose fastenings lead to vibration, which causes breakages;
- there was no leakage of liquid from the fittings. If necessary, tighten the nuts to the limit without deforming the pipelines.
Parts are replaced with new ones at the slightest doubt about their suitability. Flexible hoses, regardless of their condition, are replaced with new ones after 100 thousand km of mileage or after 5 years of vehicle operation.
Wheel cylinders
To check, the wheel cylinders are disassembled: the protective caps 5 (see fig. 147) and pistons 4, remove seals 3, support cups 2 and spring 6, then unscrew air release nipple 1.
The working surfaces of the cylinder and pistons are checked. The surfaces must be completely smooth, without visible scratches or roughness. Minor damage to the cylinder mirror is eliminated by grinding.
The elasticity of the spring is checked; its length in a free state should be 34 mm, and under a load of (3.5±0.2) kgf – 17.8 mm.
Replace the seals with new ones, also check whether the cylinder protective caps are damaged and, if necessary, replace them with new ones.
Before assembly, generously lubricate all parts with brake fluid. In the reverse order of disassembly, install the parts into the cylinder body without force, so as not to damage the rubbing surfaces. Install protective caps. Using both hands, check the movement of the pistons, which should be smooth, without jamming.
Pads
Carefully check the pads for damage (deformations). The elasticity of the tension springs, both upper and lower, is checked. The springs should not have any residual deformations when stretched with a force of 35 kgf for the lower springs and 42 kgf for the upper ones. If necessary, they are replaced with new ones.
The linings are inspected. If dirt or traces of grease are found, the linings are thoroughly cleaned with a metal brush and washed with white spirit. In addition, there is a check for grease or oil leaks inside the drum. Malfunctions are eliminated. The pads are replaced with new ones if the thickness of the linings has become less than 1.5-2 mm.
Brake drums
The brake drums are inspected. If there are deep scratches on the working surface, the drums are bored on a machine, and then the irregularities are removed from the working surface using grinding bars (grain size 10-16). This increases the durability of the linings and improves the uniformity and efficiency of braking.
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The maximum permissible increase in the nominal drum diameter (250 mm) after boring and grinding is 1 mm. The limits of this tolerance must be strictly observed, otherwise the strength of the drum and the braking efficiency are impaired.
Drum wear is allowed up to a diameter of no more than 251.6 mm.