There aren’t too many things more aggravating and embarrassing than squealing disc brakes. I am not talking about the brakes that are about due for replacement but the ones that you have recently replaced. Of course, they rarely squeal immediately after completion of a brake job. That would just be too easy. If that were the case, then you could take the necessary steps to correct this irritating racket and get on with your life. They will lay dormant, waiting for the local drive through window, cheerleader coordinated car wash, or family picnic. Then, when the time is just right, when the optimum number of strangers are present — SQUEEEEEEAAAAALLL!!! — Until you feel like you want to crawl under the seat, especially if you did the latest brake job.
Here are some simple tips to help you overcome that annoying squeal. Regardless of whether you are a do-it-yourselfer or a professional technician, there may be something here that will help you take the squeal out of your next disc brake job.
Let’s talk rotors. If you fail to correctly prepare the rotors for a brake job, then don’t be surprised if your brakes squeal. If you don’t mind noisy brakes, then by all means just slap a set of new pads on there and put the wheels back on. In order for a set of pads to be correctly burnished in they must be afforded a fresh rotor surface. The only means of obtaining a fresh rotor surface is by machining (turning) the rotors or by replacing them. With fresh pads and a fresh rotor surface you have a much better chance of performing a quiet brake job.
- If your brake pedal was already pulsating prior to the brake job, the rotors must be turned.
- If your brakes were grinding when applied, the rotors must be turned or replaced.
- If you see heat cracks and/or signs of overheating (discoloration, pitting, etc.) the rotors must be turned or replaced.
You also have to know a little about how the rotor should be machined. Rotors should always be measured to ensure that they are thick enough for machining. Your local auto parts store or auto repair facility can measure your rotors for you using a brake caliper. Once it has been determined that the rotor can be turned, they should also be able to perform the machining for a fee, of course. Before having any machining performed, it is a good idea to check the cost of a new rotor. Some rotors can be replaced so economically that it is unreasonable to have them machined, just replace them instead. If the new rotor box says these words: “No need for machining, Ready to Install, or Factory Machined” then the rotors will be ready to install, right out of the box. Never let anyone convince you that new rotors must be turned before installation, unless they are bolted to a hub assembly. That is hogwash.
If your original rotors are machined, make sure that the entire stopping surface is even. Some technicians only cut the area that is obviously worn from braking. This can leave a lip on the inner edges of the rotor, trapping heat during operation and causing pads and rotors to overheat and squeal prematurely. Make sure that the cutting bit on the lathe is positioned off the edges (especially on the hub side) of both stopping surfaces so that the entire stopping surface is machined. This tip will correct approximately 40-percent of customer comebacks with complaints about squeaking brakes.
If you ask a dozen professional automotive technicians which type of brake pad is best, you will likely get twelve different answers. The type of pad used is less of a factor than how it is installed. The correct use of noise reduction shims, hardware, and lubricants is vital to performing a brake job that will satisfy the customer (or yourself) with quiet brake operation. Brake pads which use integrated shims and are designed with chamfered edges work well but are often more expensive. A good example of high-quality pads that use integrated shims and chamfered edges are the Wagner ThermoQuiet brake pads. The key is to keep pads from binding into metal surfaces on calipers and brackets. Pads that become trapped against moving rotor surfaces are quickly overheated, will squeal, and may even fade prematurely. Caliper pistons are prone to cut into the backs of steel shims, bending, twisting, and distorting them, resulting in pad squeal. Simply lubricating the area of the brake pad that contacts the piston, with a high-temperature silicone lubricant, can rectify this situation. This is an unorthodox procedure that will dramatically reduce the likelihood of brake repair comebacks. Always use the correct hardware on brake pads. If the factory hardware is missing or broken, replace it. If you must reuse shims, then make sure that they are firmly attached to pads using high-temp adhesives. Shims that slip and distort will certainly cause brake pads to squeal.
You may wonder what the caliper has to do with pad squeal. That is pretty simple. Caliper slides that bind will force pads against moving rotor surfaces. Caliper pistons that fail to release effectively can also cause pads to overheat, resulting in premature brake squeal. Uneven brake pad wear is a common sign of a caliper or front flex hose malfunction and must be investigated. Always inspect caliper seals for signs of leaking and tearing. CAUTION: When compressing pistons into calipers make sure that bleeder valves are opened so that fluid can escape, instead of being forced back into the ABS hydraulic unit and/or master cylinder. All caliper slides and bolts should be cleaned, inspected, and lubricated with a temperature resistant silicone lubricant. Make sure that slides are operating properly by hand before reinstalling brake calipers. Make certain that all pad retention hardware is in place before reinstalling calipers. Pad return springs, such as the ones used on Nissan Maxima cars and Ford F-150 pickup trucks, are vital to pad wear life and brake noise reduction. No matter how insignificant that you believe a piece of brake hardware to be, many hours of research and development have been spent designing it. Put it back the way it was designed, if you want quiet brakes.