Table of contents: Signs of a problem with the brake… ↓ Brake lines and hoses ↓ Checking the brake mechanisms ↓ Checking the brake booster ↓
Caution: Dust from brake lining wear that accumulates on brake components may contain asbestos, which is hazardous to health. Do not blow out this dust with compressed air or inhale it! Do not use gasoline-based solvents to remove dust.
Note: In addition to routine checks, the condition of the brakes should be checked every time the wheels are removed or if there are signs of a fault in the brake system. Checking the brake fluid level is described in Section 4.
Signs of a problem with the brake system
1. Any of the following symptoms may indicate a potential defect in the brake system:
- when pressing the brake pedal while driving, the car "pulls" to the side;
- the brakes make scraping or squealing sounds when braking;
- the brake pedal has excessive travel;
- the brake pedal pulsates (this is normal only when the ABS system is working);
- brake fluid leaks are observed (usually visible on the inside of a tire or wheel).
2. If you notice any of these signs, inspect the brake system immediately.
Brake lines and hoses
Note: The brake system uses mostly metal brake lines, with the exception of flexible reinforced hoses near the wheels. Regular inspection of all these lines is very important.
3. Park the car on a level surface.
4. Jack up the car and place it on stands, then remove the wheels. Checking the vacuum hoses is described in Section 5.
5. Check all brake lines and hoses for cracks or abrasions in their outer coating, as well as leaks, bulges, and deformations. Check the brake hoses at the front and rear of the vehicle for signs of softening, cracks, deformations, or wear due to friction with other parts. Check all fittings for signs of leaks and make sure that all brake line fasteners are secure.
6. Bend the brake hose in both directions with your hands to check for damage. Do not twist the hoses.
7. Turn the steering wheel from lock to lock. Make sure that the front brake hoses do not touch the vehicle's structural elements.
8. If any damage or fluid leaks are found in the brake lines, these faults should be repaired immediately. For a more detailed description of the brake system repair procedure, refer to Chapter 9.
Checking the brake mechanisms
9. The thickness of the outer brake pads can be determined without removing the wheel. In this case, you need to roll the car so much that the brake mechanism is visible in the wheel rim opening (see illustrations). If necessary, use a caliper. Compare the measurement result with the requirements Specifications and if necessary, replace all the pads of both brake mechanisms of the wheels of this axle (see Chapter 9).
8.9a. Front wheel brake pad thickness
8.9b. Rear wheel brake pad thickness
Note: As a rule, 1 mm of brake pad wear corresponds to at least 1000 km of mileage under unfavorable operating conditions. Under normal conditions, the pads wear out much more slowly.
10. For a more accurate measurement of the thickness of the pads, jack up the car and place it on supports, then remove the corresponding wheel.
Note: Experience shows that due to the presence of dirt on the edge of the road, the brake pads of the right wheel wear more than the left. Therefore, it makes sense to remove the front right wheel for inspection.
11. With the wheel removed, check the wheel cylinders of the brake mechanisms for leaks. If leaks are found, repair the wheel cylinders immediately.
12. Visually inspect the brake discs from the inside and outside for grooves, rust and cracks. Replace defective discs.
13. Measure the thickness of the brake discs in several places using a micrometer or a special caliper. You can also measure the thickness of the brake disc with a regular caliper, placing a lining of a known size on each side of the disc (for example, two coins), and then calculating the difference between the measured value and the thickness of the linings.
14. Compare the minimum of the results obtained with the requirements Specifications for Chapter 9. If the wear limit is reached, replace both brake discs. The brake disc should also be replaced if there are large cracks or deep grooves on the working surface.
15. The rear disc brakes, which are also used in the parking brake, are self-adjusting. The parking brake does not require inspection, and adjustment is only required after replacing the parking brake cables, as well as the calipers, pads or discs of the rear brake mechanisms.
Checking the brake booster
16. With the engine off, press the brake pedal several times - with each press its travel should decrease.
17. With the brake pedal depressed, start the engine - the pedal should move down.
18. Keep the brake pedal depressed and turn off the engine. If the pedal travel does not change after holding it for 30 seconds, the vacuum booster is OK.
19. If any of the above checks fail, repair or replace the vacuum booster (see Chapter 9).
20. If you have a vacuum gauge, you can more accurately assess the proper functioning of the brake booster, as described below.
21. Disconnect the hose from the tip and connect a vacuum gauge between the tip and the vacuum hose coming from the check valve.
22. Start the engine and make sure that the vacuum increases. Stop the engine.
23. Press the brake pedal, create a vacuum of no more than 0.8 bar and wait until the value stabilizes. When the brake pedal is released, a vacuum drop of no more than 0.06 bar is allowed during 1 minute of testing. Otherwise, check the tightness of the vacuum line connections, replace the check valve, check the condition and tightness of the sealing gasket (ring) between the brake booster and the master cylinder, or replace the brake booster (if the specified values are not reached again during the repeated check).