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When should brake discs be replaced?
The service life of the front brake discs is on average 50,000–70,000 km, and 70,000–100,000 km for the rear ones. However, sometimes they will need to be changed earlier. New discs need to be installed if they wear down to the minimum thickness specified in the vehicle’s service manual. It is recommended to measure this with a vernier caliper once every 10,000 km. Also, cracks and chips, uneven wear and warping indicate that the components need to be replaced.
The procedure for checking the brake disc wear:
There are also indirect symptoms to let you know that your brake discs need checking or replacement. For instance, if you feel wobbling, grinding, rattling or vibrations during braking, this may indicate that the parts are warped. In this case, you might need to take additional measurements, for instance, with the help of a dial indicator. Before proceeding with the measurements, thoroughly clean the wheel hub and the disc. Mount the device on a stand and position its spindle perpendicular to the disc surface about 5 mm away from its edge. The tip of the spindle should contact the surface. Then, rotate the wheel hub. The dial indicator should not show the deflection of over 0.06 mm.
Weak and uneven braking, as well as a vibrating brake pedal, often indicate uneven wear of the friction surface of the discs.
Do I need to replace brake discs and pads together?
When replacing brake discs, it is recommended to install new pads at the same time. The old ones will have developed a wear pattern that corresponds to the old discs. Therefore, using these pads again risks premature wear of the discs and a decrease in braking performance. How long the procedure will take depends on the vehicle design and your mechanical skills. On average, installing new brake discs and pads takes from 15 minutes to 3 hours.
Can I only replace one brake disc?
No, you cannot. Brake discs should only be replaced in pairs on an axle. Otherwise, due to a smaller thickness of the old part and, therefore, different lengths of the piston stroke, the brake mechanisms will fail to act simultaneously, which will lead to instability of the vehicle when braking.
Is driving with worn brake discs dangerous?
Yes, it is quite dangerous, that is why worn discs should be replaced immediately. A brake disc that is too thin is unable to dissipate heat efficiently, which can make it crack or break after overheating. As a result, the wheel will lock and the car will skid. Uneven wear and deep grooves reduce the area of contact with the pad, which leads to decreased braking performance. Warping will cause lateral run-out which leads to uneven wear of the part’s working surface and increased travel of the brake pedal (“spongy brakes”). As for corrosion, the disc can still be used if it is insignificant, however, you should clean its surface by pressing the brake pedal all the way down while driving. But if the braking performance dropped significantly because of corrosion or the braking mechanisms work incorrectly, the components should be replaced as soon as possible.