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Servicing Disc Brakes
Disc brakes bring a vehicle to a stop when pressure is applied to both sides of disc-shaped rotors at either end of the axle. A caliper, housing two brake pads, is situated on top of the rotor. When the brake is applied, pistons inside the caliper squeeze the pads against both sides of the rotor to slow and stop the vehicle.
Brakes should be serviced about every 10,000 miles or so. Servicing disc-style brakes generally involves replacing brake pads and checking the rotors to see whether they are in need of resurfacing (or replacement, if they are severely damaged). If there are deep scratches, grooves or scoring on the rotor, it should be resurfaced. Resurfacing is something that should generally be done by a brake technician since it requires a brake lathe -- a highly specialized piece of equipment.
A dial indicator is used to check the rotors to make certain that they are not warped or out of round. With the dial indicator set to zero, the disc is rotated. If the disc is still even and is not warped, the dial indicator will remain close enough to the zero setting to indicate it is within proper, specified limits.
After checking the rotor with the dial indicator, the caliper is removed to gain access to the pads and rotor. The caliper is held in place by retaining bolts that are easily removed. Once the bolts have been removed, the caliper remains attached to the brake lines. Letting the heavy caliper hang suspended by the brake line could damage the brake line, so electrician's wire can be used to suspend the caliper so that it's free of the rotor and out of the way.
Once the rotor has been removed, its exact thickness needs to be measured. Since resurfacing is accomplished by removing a thin layer from the rotor's outer walls, it's necessary to ascertain that the amount being removed won't reduce the thickness of the rotor below proper and safe operating specifications. Minimum-thickness specifications (in millimeters) are usually stamped right into the metal rotors. A micrometer or a digital slide caliper is used to measure the thickness of the rotors to see how much useful life they have left in them.
Once the rotors have been measured and it has been determined that there is enough thickness left to allow resurfacing, the rotors are turned on a brake lathe. The lathe has hardened carbide blades that shave off tiny amounts of metal from both surfaces of the rotor as it turns. Precision controls allow the lathe operator to dial in and determine in thousandths of an inch exactly how much metal is to be removed.
Once the rotor has been resurfaced and reinstalled, new brake pads are seated and installed in the caliper, and an antisqueal lubricant may be applied. Before finishing the job, it's a good idea to clean the rotor and the area around it with brake cleaner.
When you're servicing disc brakes, it's also a good time to check and repack the wheel bearings and seals. The bearings serve to cushion the contact between the wheel and the spindle it sits on at the end of the axle. They are packed with grease to reduce wear from friction as the wheel rotates. Since the wheels on your vehicle may turn as many times as 900 times per mile, it's easy to see why these parts are so important. Since the grease used to pack the bearings picks up dirt and other contaminants, it's best to replace it about once a year to help extend the life of the bearings -- about the same interval as that for servicing brakes.
Repacking bearings on disc brakes requires removing the wheel-bearing nut and the wheel hub. The wheel bearing can then be removed from the center of the hub by prying it loose with a screwdriver. The bearing, hub center and end of the spindle are then cleaned with parts solvent, inspected for damage and allowed to dry. Provided that the bearings are not so worn that they need to be replaced, they can be repacked by rolling the bearing in a mound of bearing grease in the palm of your hand -- a very messy job. Consult your vehicle's service manual before attempting to remove, repack, and reinstall bearings. Some vehicles have sealed bearings that do not require maintenance.
Important :
The braking system is perhaps the most important system on your vehicle from a safety standpoint. Since improper repair or installation of critical elements in the braking system could ultimately result in a serious accident, it's vital to make sure that any brake job is done right. For this reason, many people leave brake work to professionals at the automotive dealership or a brake specialty shop. In addition, there is considerable variation among braking systems on different vehicles, particularly on newer vehicles that use sophisticated hydraulic and electronic control systems.
Simple elements in brake repair, such as replacing pads or shoes, are jobs that the automotive do-it-yourselfer can do -- provided that the instructions in the vehicle's service manual are consulted and followed. Major brake work, however, generally is best left to professionals who have the expertise and equipment to do it properly. The description of the steps in this project is intended to provide an understanding of some of the procedures that are involved in typical brake repair.
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