1. Replace worn brake pads.
2. Repairing caliper assembly.
3. Turning (machining) brake discs.
4. Bleeding the system.
Depending on the condition of these parts and as per need, do one or more of these operations. Service manual must be followed because procedures may vary. In any case you must make sure the brake assembly is in sound operation condition. Replacing Brake Pads To replace worn brake pads first loosen the bolts. Place the car on the car jack stands and remove the wheels and tires. Before caliper removal, use a large C- clamp to push the piston back in to its cylinder. Then the piston will be retracted and out of way, allowing the new, thicker pads to fit in to the caliper. Unbolt and slide the caliper-off of the disc. To prevent brake hose damage, hang the caliper by a piece of mechanics wire (simple wire) if not to be removed.
Remove old pads. Install anti-rattle clips on new pads. Fit pads back in to caliper. Slide the caliper assembly over the disc. Assemble the caliper mounting hardware in reverse order of disassembly. Make sure all bolts are torqued (tightened) properly. Install wheels and tighten wheel by nuts to specifications. Repeat these operations on the other disc brake assemblies as needed. Note It is acceptable to service the just front or just near brakes. But never service only the right or let brake assemblies. This will cause dangerous brake pull. Repairing a Caliper Assembly When a caliper piston is frozen, leaking or has extremely high mileage, it must be rebuilt (repaired). Remove the caliper from the car and take it to a clean work area. To remove the piston from the caliper, use just enough air pressure to push the piston out of its cylinder. Danger Keep your fingers out of the way when using compressed air to remove caliper pistons. A stick piston will fly out with great force, which can injure your hands.
After piston removal, remove the old dust boot and seal out of caliper keep all the parts organized on your workbench. Do not mix up right and left hand side or front and rear parts.
Check caliper cylinder wall for wear, scoring or pitting. Light surface imperfections can usually be cleaned up with a cylinder hone.When honing, use brake fluid to lubricate the hone. If excessive honing is needed replace the caliper.
Also check the caliper piston for wear or damage. Install a new one if you find out any problems. The piston and the cylinders are very critical and must be in perfect condition.
Clean all the parts with an approved cleaner wipe the parts clean with a elocutions rag. Then coat them with brake fluid. Assemble the caliper in reverse order of disassembly. Typically, fit the new seal in the cylinder bore groove, work it in with your fingers. Then install the new boot in it grooves. Coat the piton with more brake fluid. Spread the boot with your fingers and slide the piston in to the cylinder. Brake Disc Service When servicing a brake system it is important to check the condition of the brake disc. Automakers provide specifications for minimum disc thickness and maximum disc Run-out (wobble). Also the disc must not be scored, cracked or heat checked. Measuring Disc Run-Out Brake disc run-out in the amount of side-to-side movement measured near the outer friction surface of the rotor. A dial indicator is used to measure disc Run-out.
Compare indicator reading to the manuals specifications. Typically, disc run-out should not exceed 004 inch (0.10mm) if run-out is more than specifications turn (machine) the rotor (disc) on a brake lathe to true (correct) its friction surface. Measuring Disc Thickness Brake disc thickness is measure across the two friction surfaces in several locations. Variation in disc thickness indicates wear.
To measure disc thickness, use an outside micrometer. Measure in several places. Compare your measurements to the specifications.
Minimum disc thickness will sonic-times has been printed on the side of the disc. If not, refer to a manual or brake specification chart. If disc thickness is under specifications replace the disc, otherwise disc cannot dissipate heat properly and may warp or fail in service. Resurfacing a Brake Disc Brake disc resurfacing involves machining the friction surfaces on a brake lathe. Disc resurfacing is needed to correct run-out, thickness variation, or scoring. When a disc is in good condition, it should not be resurfaced.
To resurface a brake disc, mount the disc on the lathe. Use the appropriate spaces and comes to position the disc on the machines arbor. Follow the directions provided with the brake lathe. Wrap a spring or rubber damper around the disc to prevent vibration.
Wear the eye protection; adjust the cutting tools until they contact the friction surface on the disc. Then with the machine feeds and control set properly, machine smooth surfaces on the disc.
Only machine off enough metal to true the disc. Then without touching the machined surfaces with your fingers. Remove the disc. Double check disc thickness, then, install the disc on the vehicle. Some front wheel drive cars have brake discs that are difficult to remove with their cars, an on the car disc lathe (grinder) is a time saver use it. It will resurface the discs with out removing them. Disc Brake Re-assembly Re-assemble the disc brake in the opposite order of disassembly. After in stalling the brake disc, fit the caliper assembly into place. Make sure the new pads are properly installed. Tight all fastener (nut & bolts) to the specifications.