Notes, Warnings, and Hints
WARNINGS, NOTES, AND HINTSNOTES
Prior to removing the calipers, remove/siphon brake fluid from master-cylinder until the reservoir is only 1/3 full.
Always replace all brake linings on an axle. Never replace only one wheel. Unequal lining thickness between wheels on the same axle will result in a strong steering pull when the brakes are applied.
Clean and lubricate caliper slide joint/pins with high temperature silicone grease:
- Unlike drum brakes, disc brakes do not utilize a spring to withdraw the pads/linings when the brake pedal is released. Disc brakes rely on the elasticity of the piston seals, and the unrestricted movement of the caliper slide assemblies to release the brakes.
- If the slide joints/pins are not cleaned and lubricated properly the disc brake linings will drag upon the release of the brake pedal. This will result in overheated brakes and premature brake wear.
- High temperature silicone lubricant must be used. Low temperature grease can melt and contaminate the pads and rotors, or can bake into a very hard substance which binds the slides. Petroleum based grease can cause the slide boots to soften and swell.
Disc Brake Mechanical Force Diagram:
NOTE: Floating calipers require free and unrestricted movement on the caliper mounting. Floating or sliding calipers have pistons only on one side of the rotor. The first part of the piston's travel forces the inner pad against the rotor, then further travel forces the movable part of the caliper to pull the outer pad against the rotor.
Anti-squeal Coating:
Apply an anti-squeal coating to the back side of the pads/linings. This coatings acts as an insulator to dampen high frequency vibrations that are generated during normal braking. These compounds are highly effective in preventing brake squeal.
Always flush and bleed the brake hydraulic syst when servicing the brakes, because:
- Brake fluid absorbs moisture from the air, after 3-4 years of service the water content of the brake fluid may be as high as 6-7%. This significantly reduces the boiling point of the brake fluid which may result in a soft pedal or brake failure during prolonged or severe braking.
- Corrosion deposits and other contaminants gradually build up inside of the brake hydraulic syst. Check the bottom of the master-cylinder reservoir for a build up of fine black silt. If any is present the brake fluid should be flushed.
Thoroughly clean the rotors with brake cleaner.
- Any grease or brake fluid which comes in contact with the rotor should be thoroughly cleaned prior to installing the new pads/linings.
- Grease and other contaminants become lodged in the microscopic pores of the rotor's surface. This prolongs the brake-in time of the new linings and contaminates the friction material.
- Commercially produced aerosol brake cleaners should be used to clean the rotor. Unlike carburetor cleaner or other petroleum based solvents, brake cleaner does not leave a residue on the rotor's surface.
Upon installing both left and right side calipers, pump the brake pedal to seat the new pads. It normally takes 3-4 full pumps to establish a firm pedal.
After pumping up the brake pedal, refill the master-cylinder. As the caliper pistons push out the new brake linings to contact the rotor, up to 30% of the brake fluid in the master-cylinder may be used.
Always tighten the lug nuts to the correct torque specification.
- Lightly lubricate the studs with high temperature wheel bearing grease or an anti-seize compound to ensure proper torque and prevent damage to the threads.
- Tighten in an alternating pattern around the wheel until the wheel is centered on the studs. Do your final tightening with a torque wrench.
- When servicing disc brakes it is very important to properly torque the wheel assembly.
Check the wheel bearings once the tires are installed.
- With the vehicle raised and properly supported, grasp the tire at the top and bottom and attempt to rock them back and forth. There should be no detectable lateral (wobble) movement.
New brake linings must be properly broken in.
- Initially make 8-10 slow and gradual brake applications, slowing from 25 to 10 miles per hour.
- Severe braking or locking up the brakes should be avoided (unless dictated by an emergency or driver safety) for the first 50 miles.
HINTS
When forcing the piston back into the caliper, open the bleeder valve first. Corrosion and other deposits accumulate inside of the caliper. If the bleeder valve is not opened when the piston is forced back into the caliper, these deposits will be forced back through the brake lines and into the master-cylinder.
Work on one side at a time. If you forget how to reassemble the parts you can always use the other side as a model.
Many professional repair shops recommend always rebuilding or replacing the calipers when replacing the brake linings, because:
- When the pistons are forced back into the calipers, the piston seals are dragged across any corrosion or abrasives that may be deposited on the inside of the caliper.
- Damage to the seals may not be initially evident. As the new brake linings begin to wear, the piston is gradually withdrawn from the caliper. This results in the piston seals again being dragged across the layer of corrosion and deposits.
- Calipers which are not rebuilt or replaced have a higher probability of sticking or leaking.
Check to ensure the bleeder screw is not frozen prior to reinstalling caliper. Freeing a stuck bleeder screw is much easier with the caliper removed from the vehicle.
WARNINGS
Brake fluid will remove paint and damage electrical connections. Use a drip pan and fender covers to protect the vehicle's finish and electrical system.
When pushing the pistons back into the caliper with the bleeder screw open, a stream of brake fluid will be expelled from the bleeder screw for 2-3 feet. Use a drip pan and be careful not to "shoot" brake fluid onto the vehicle's finish. A cleaner method is to use a piece of clear plastic hose and a glass or plastic jar to catch the expelled fluid.
Upon removal, Do Not allow the calipers to hang by the flexible brake hoses. The brake hoses can be damaged easily by this practice. These hoses are double walled, damage to the interior pressure hose will not be visible.
Do not depress the brake pedal with either caliper removed from the rotor. The caliper pistons will be inadvertently expelled from the caliper. If this occurs rebuild or replace the caliper, do not attempt to insert the piston back into the caliper.
Never reuse brake fluid that has been drained from the brake system.
Do not attempt to move or test drive the vehicle until a firm pedal is established. The vehicle will have NO BRAKING ABILITY (front or rear) until the brakes are pumped and a firm pedal is established.
Lug nuts which are installed with an air impact tool are often over-torqued. This may distort the rotor and result in excessive lateral runout (rotor wobble) and a pedal pulsation upon braking. Remember, a torque specification is a precise measurement, it does not mean, "at least as tight as...".
Prior to test driving after servicing, check the following:
- Check the tire pressures. Uneven tire pressures may result in a noticeable pull when the brakes are applied.
- Inspect the calipers and all brake hydraulic connections and verify that there are no brake fluid leaks.
- Verify the operation of the rear brakes and emergency brake, and adjust if necessary.
- Verify that all lug nuts have been tightened, and torqued to specifications.
- Verify that the master-cylinder is properly filled.
Pedal Reserve Checks:
- Ensure you have a firm brake pedal with at least a 75% reserve.
- Check for proper brake booster operation (NON-ABS ONLY):
1. With the engine "OFF", depress the brake pedal 4-5 times.
2. Depress the brake pedal firmly and start the engine.
- If the pedal goes down slightly, the brake booster is operating properly.
- If the pedal does not go down slightly the brake booster is not assisting in brake operation and should be diagnosed for problems.
Until the new brake linings are properly broken in, overall braking performance will be less than 100%. Braking performance will gradually increase as the new linings seat.
DOT 3,4 or DOT 5
As a general rule DOT 5 brake fluid should not be used in vehicles recommending DOT 3 or 4 type fluid.
DOT 5 brake fluid is silicone based. DOT 3 (standard) and DOT 4 (heavy-duty) are glycol-based. It can be distinguished from conventional brake fluids by its purple color (which comes from a dye).
DOT 5 silicone brake fluid won't mix with glycol-based brake fluid (creating concern over sludging if all old fluid isn't removed when a system is refilled with silicone).
Silicone does not absorb moisture. DOT 5 brake fluid does not become contaminated with moisture over time as conventional DOT 3 and 4 brake fluids do. Silicone is also chemically inert, nontoxic and won't damage paint like conventional brake fluid. It also has a higher boiling point.
Because of this, it is often marketed as a premium "lifetime" brake fluid. It is often used to preserve brake systems in antique vehicles and those that sit for long periods of time between use.
Silicone also has slightly different physical properties and compressibility, making it unsuitable for ABS systems calibrated to work with DOT 3 or 4 brake fluid.