Before replacing old brake pads, take a moment to examine them, along with your calipers, to diagnose any issues that could result in brake failure. A thorough check also helps prevent prematurely replacing still-functioning brake components.
The automotive experts at FDP Virginia Inc., which develops and sells Goodyear Brakes, offer some tips for assessing the health of your vehicle’s braking system, as well as advanced solutions for addressing any issues.
What wear patterns should I look for?
In normal brake pad wear, the inside and outside pads on both calipers have worn at relatively the same rate for all four pads. Each pad should be worn smoothly, without any taper, grooves or cracks.
What do I do if my old brake pads have abnormal wear?
If your old brake pads exhibit an abnormal wear pattern, you must remedy the cause. If the outside pad wears more quickly, it indicates a problem. This wear pattern will show on floating calipers, which have one or two pistons that apply the pad to the inboard side. The outboard side of the caliper moves the pad on slides or guide pins to contact the outside of the rotor. If these slides or guide pins are not kept lubricated with high-temperature ceramic or silicone brake lubricant (grease), or corrosion has damaged these moving surfaces, the outside pad can drag on the rotor. Corrosion is a problem particularly in areas where road salt and liquid brine are applied during winter months. A pad that has been dragging may overheat and glaze and/or crack the friction material surface.
Why are my pads worn in a taper?
Brake pads rely on hardware being in good condition and calipers that operate smoothly and squarely to the rotor. If the bushings or hardware in the caliper are worn, this will cause the brake pads to wear to a taper as they apply at an angle to the rotor and eventually wear to conform to that improper angle.
Get out of the groove
If your rotor has grooves in it, the old brake pad likely wore over time to conform to them. This will prevent maximum braking efficiency and can cause abnormal noise. Consider replacing the entire braking system to restore braking performance.
Any rotor that shows signs of overheating, such as bluish or darkened spots, should be replaced, as these hot spots are now harder than the rest of the rotor. The hot spots will not wear as quickly and cause “warped” rotors, although it’s actually caused by a variation in the thickness of the disk. Be sure the mounting surface of the rotors and hubs are clean of any rust, corrosion, or dirt, so they run true.
What if one side’s pads have worn out at a much higher rate?
If one side of your braking system has worn the pads at a much higher rate than the other, suspect a problem with the caliper or the brake hose. The following tips apply if the inside and outside pad of the left caliper, for example, are worn fairly uniformly, but are worn much worse than the right side. This will also often result in a pull to one side under braking.
Normal wear and heat from operation can cause rubber to degrade in the caliper’s piston outer accordion boot and inner seal, which can cause leaks. Corrosion can cause the caliper’s piston to pit. Although this damage is not usually apparent – even after peeling back the protective outer boot – it can cut the piston seal and cause a leak. It is this same piston seal that retracts the piston once brake fluid pressure is released by releasing the brake pedal. If the piston should stick open, the brake pads will drag on the rotor.
How do I determine which is the faulty part?
You will need to compress the caliper’s piston(s) to install the new pads. But first, loosen the caliper’s bleeder valve. This relieves brake pressure on the piston so you’re not trying to push all of the brake fluid in the path between the caliper and the master cylinder. It’s not good for your braking system to force that dirty fluid back into the braking system, which for modern vehicles includes anti-lock brake modules that can be sensitive to contaminated fluid. Watch the piston as you relieve pressure by opening the bleeder valve. If the piston quickly retracts, the caliper is operating normally, and other parts are suspect.
How a brake hose fails – and how to check
First, make sure the brake hose is not kinked, which could happen by an installation error. Then look at what happens to a hose to mimic a sticking caliper. The outside of the rubber brake hose may still look smooth and supple, but the inside may have collapsed. Or it may have started to break down, and a small piece is partially stopping up the hose. This can cause a restriction at the caliper upon initial brake pedal application, which will apply that caliper later than the one with the good hose. Then when pressure increases, it is enough to overcome this partial blockage, and the brakes apply normally. But when the brake pedal is released, fluid is now retained at the caliper – and the pad – because of this restriction acting as a check valve.
If the piston is relatively easy to compress with your brake compression tool or a c-clamp, and at the same effort for the left-hand and right-hand calipers, suspect a faulty hose. They’re cheap enough and easy to replace. Although less common, also look for any damaged metal brake lines that could be causing a restriction.
A problem with the master cylinder could also exist, although because of its design, the problem would not be isolated to only one corner of the vehicle, such as the left-hand caliper. The hydraulic circuits of modern braking systems are either split front-to-rear or diagonally split (common on front-wheel-drive cars), so a problem with the master cylinder would show on both front calipers, or a left front and right rear caliper in a diagonally split system.
Whatever parts you do replace, it is recommended doing so in pairs. If one part has failed, the other may be ready to soon fail, too. Replacing both calipers will help provide equal braking performance so that you don’t have a pull to one side.
Source: Goodyear Brakes