Brake Calliper Service – The Often Forgotten Component of Safe Brakes
Like many of us, we are not experts in car maintenance and we don’t always understand all the maintenance that is required to keep our vehicles running efficiently. Did you know that it is recommended to maintain your brake callipers every 2 years or 40 000km on your vehicle? Brake calliper servicing is something that is needed and different from your typical brake service.
Let’s start with the first question that we are all asking…what are brake callipers? Brake callipers house the brake pads and, using brackets, pistons and calliper slide pins, which help push the pads into the brake rotors when you apply the brakes.
Let’s dig in more to fully understand the brake callipers. Over time, the slide pins that we are referring to use their lubrication and don’t slide the callipers well. With lack of lubrication, a few things start to happen.
- Brakes don’t contact the rotor correctly; brake pads wear unevenly.
- The slide pins can stick. This causes the brake pad to continually contact the rotor, resulting in a buildup of heat, which wears down the brakes even faster.
- Your brake’s stopping power may become weak due to the brake pads not hitting the full surface of the brake rotor.
Bottom line, it sounds like we are not fully getting use of the brake pads as we should, which means we are throwing dollars away.
What is Done During a Brake Calliper Service?
- Brake Calliper Inspection
Brake pad wear can be an indicator of calliper condition. If the inboard pad is more worn than the outboard pad, the floating calliper may be seized. Either type of calliper — fixed or floating — will cause the brake pads to drag against the rotor when the pistons are seized into the calliper bores.
In addition, the calliper boot should not show any signs of fluid leakage nor should the calliper boot appear hardened or cracked. The piston will eventually corrode and seize in place if a defective calliper boot allows moisture to accumulate between the calliper bore and piston.
Callipers with integrated parking brake hardware should be inspected for fluid leakage and correct parking brake operation, and service brake pedal travel. In some applications, the parking brake must be used regularly to compensate for brake pad wear. Excessive service brake pedal travel may result if the driver doesn’t use the park brake regularly or if the parking brake cable or calliper hardware is seized.
- Brake Calliper Service
Although you’re not likely to rebuild a disc brake calliper in the near future, it still pays to understand how in case, you find yourself rebuilding the original callipers on a classic or collector import vehicle.
First, it’s important to establish safe work habits before beginning any hydraulic brake service by consulting an appropriate service manual. The pressure in the anti-lock brake accumulator should be released by pumping the brake pedal as specified by a service manual or until the pedal feels hard. Next, the bleeder screw should be loosened to allow old fluid to be flushed out of the calliper bore. In some cases, a clogged bleeder screw must be removed for cleaning or replacement. If the bleeder screw is seized, it’s probably cheaper to replace the calliper.
There are two schools of thought on preventing debris from being flushed into the anti-lock braking and master cylinder assemblies when the piston is seated in the calliper bore. The first “school” opens the bleeder screw to relieve pressure as the calliper piston is seated. The second “school” clamps the brake hose closed with a pair of hose-clamping pliers to prevent debris from back-flushing into the master cylinder. The first-school method is the most commonly accepted because there’s less chance of inadvertently damaging the hose.
- Caliber Disassembly
Seized calliper pistons can be difficult and dangerous to remove, so be cautious. Perhaps the safest method is to bottom the piston with a common C-clamp to push out excess fluid, and then ease the piston from the bore by gently applying air pressure to the brake hose port while backing out the C-clamp screw.
When the piston is ready to exit the bore, cover the calliper assembly with a shop towel to prevent the brake fluid from spattering. If the piston is so badly seized that it doesn’t respond to controlled air pressure, the calliper should be replaced.
Because the piston surface seals the brake calliper, the piston should be in like-new condition. If the piston is pitted or scored, it should be replaced.
Replacing the boot often requires a dedicated tool to press the boot into the calliper bore. In many cases, a seal driving tool or an old bearing race can be used to press the boot into the bore without damaging the boot.
The most common method for installing the piston into the boot is to hold the piston in place with a piston seating tool while inflating the boot with compressed air. This method works well on small-bore callipers. Boot expansion tools must generally be used on large-bore callipers with shallow-boot designs.
The piston must be perfectly square with the bore before it will pass through the flat-cut O-ring in the calliper bore. The simplest method is to use a square bar to gently rock the piston from side-to-side until it drops into the calliper bore. A wooden 2×4 plank works well on larger bore calliper pistons.
Once the piston is installed, carefully remove the calliper guide pins and lubricate them with synthetic calliper grease or the OEM-recommended lubricant. When installing the calliper bracket bolts, apply thread-locking compound, if required. In other cases, lightly oil the bolts and torque them to specification. Always install new calliper hardware on the calliper bracket to prevent pad rattle and dampen pad squeal.
A correctly serviced calliper should slide smoothly on its guide pins or guide surfaces, and should allow the rotor to turn freely when brake pedal pressure is released. If the calliper won’t release, the interior rubber of the brake hose might be peeling and blocking the return of fluid to the master cylinder reservoir. In other cases, the master cylinder push rod or brake pedal height might be incorrectly adjusted, which prevents the master cylinder from releasing the fluid pressure from within the calliper.
Source credit in full: http://www.crestmontcadillac.com/blog/maintenance-on-your-brake-calipers-is-395150