Replacing a set of brake pads is a common brake repair procedure. But if not done correctly, it can cause problems. Brake systems are very sensitive to rust and corrosion and should receive a thorough cleaning when new pads are installed. Residual rust or corrosion left in critical areas can cause brake issues almost immediately.
A growing number of late model cars are equipped with antilock brake systems that can precharge the brakes in anticipation of braking (to reduce braking reaction time), or actually apply the brakes automatically as a function of the collision prevention system (automatic braking).
CAUTION: If you are replacing the brake pads on these vehicles, the braking system must be deactivated before you work on the brakes, otherwise the system may energize the brakes unexpectedly causing the caliper pistons to push outward with considerable force. This could pinch your fingers if they are between the pads and rotors. If the pads have been removed, the pistons can blow out of their calipers. This can happen even when the ignition and engine are off!
The antilock brake system can be deactivated by locating and removing the main power fuse for the ABS system, or by using a scan tool to temporarily deactivate the system. Disconnecting the battery also works, but this may cause loss of certain memory settings in various vehicle modules. See Battery Disconnect Cautions & Problems for more information on this subject.
The basic procedure for replacing the front brake pads goes as follows:
1.Park your vehicle on a level surface, set the parking brake and place the transmission in Park (in gear if manual shift). Then loosen the lug nuts while the weight of the vehicle is still on the wheels. Do NOT remove the lugs nuts yet!
2.Raise the vehicle with a floor jack until the front wheels are off the ground. Support the vehicle with TWO safety stands. Do NOT rely on the jack alone to support the vehicle.
3. Remove the lug nuts and remove the wheel from the hub.
4. Determine how the brake calipers are mounted, and remove the pins or bolts that hold the calipers in place. On some applications, you can remove one pin or bolt and rotate the caliper up away from the rotor to replace the pads. On others, both bolts must be removed so the caliper can be lifted up and away from the rotor to change the pads.
CAUTION: Do NOT allow the calipers to hand by their hoses as this may damage the hoses. Rest the calipers on a suspension component (if possible) or support them with a piece of heavy wire.
5. Remove the inner and outer pads from the caliper. They may be held in place with wires or clips. Be careful not to damage these clips. Save them for reuse when the new pads are installed.
6. Once the pads have been removed from the calipers, inspect the calipers carefully to make sure they are not leaking any fluid, and that the piston dust seals are not cracked or damaged. If a caliper is leaking, it will have to be replaced or rebuilt with new piston seals. Cracked dust seals should also be replaced to help protect the pistons.
7. Use a large C-clamp to carefully push the caliper pistons back into the calipers. This is necessary so there will be enough clearance for the new (thicker) brake pads. It may be necessary to remove some fluid from the master brake reservoir so it does not overflow when the pistons are pushed back into the calipers as this will displace brake fluid back to the master cylinder.
8.Install the new inner and outer brake pads into the calipers. Replace any shims, springs or clips that were used with the original pads to hold them in place (unless new hardware or shims came with the new pads, in which case discard the old shims or hardware and replace with new). Apply a light coating of moly based brake lubricant (never ordinary grease) to the BACKS of the pads and to the points where they contact or rest against the calipers. Do NOT get any grease on the front (friction side) of the pads as this will ruin the pads and cause uneven braking.
9.Lubricate the caliper mounts and pins, and reinstall the pins or bolts, slide the caliper back into place over the rotor and tighten the mounting bolts to specifications with a torque wrench. If the original pins, bushings or bolts are badly corroded or damaged, replace them with new. Do NOT reuse badly corroded or damaged mounting hardware.
9. Remount the wheels on the hubs, tighten the lug nuts, then lower the vehicle until the tires are on the ground and final tighten the lug nuts to specifications with a torque wrench using an alternating star pattern (necessary for even loading and to prevent rotor distortion).
10. Start the engine and pump the brake pedal several times until the pedal feels firm. Do NOT drive the vehicle without first pumping the brakes to make sure your vehicle will stop when you apply the brakes! Then do a short test drive and do a series of gradual stops from about 30 mph with gradual braking. Do NOT slam on the brakes and avoid hard braking for the first couple hundred miles of driving.
The following brake pad installation tips are provided courtesy of Bendix:
Calipers. Areas that are subject to movement or retain components or hardware should be cleaned, along with the pin bores. Therefore, calipers need to be disassembled during pad replacement. Use a round wire brush and cleaner to remove old lubricant and corrosion. Use a fine polishing disc in a die grinder at a lower speed to clean the area. Avoid being too aggressive, especially with aluminum components, to ensure you only remove corrosion and not any metal. Be sure any areas on anti-rattle clips or hardware are free of debris as this can affect their performance over the life of the brake job.
Calipers on Ford 3/4 and 1-ton trucks have seen slides freeze shortly after brake service if they are not properly cleaned.
Pad Abutments. Whether they are part of the caliper bracket or steering knuckle, pad abutments need to be clean and smooth. If there are any notches or grooves caused by pad movement, these parts should be replaced. Damage like this can cause excessive pad movement that leads to noise and vibration.
Hub assemblies. Use a polishing pad to clean rust from the hub face. Then use an over-the-stud hub cleaner to get in next to the studs. Leaving corrosion in these areas is one of the top causes for pulsations after a brake job is completed.
Mounting Pads. One area that is often overlooked is the mounting pad on the hub that mates with the wheel. If there is rust or debris on this surface, it can lead to rotor distortion and pulsations just as easily as if it were left on the hub.
Rotors. New or machined rotors should be washed with soap, warm water and a stiff brush to remove metal particles from the surface. If this final step is not taken, brake noise may likely result. It can also prevent proper filming of the rotor which will keep the new parts from getting their expected mileage.
Bendix also recommends you clean the rear calipers and drum and parking brake systems. All these components should receive a good cleaning, inspection, lubrication and adjustment before the vehicle hits the road.
For more information and tech tips, visit www.bendixbrakes.com.