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Braking System




Drum Brake Components

Q: I have a truck with rear drum brakes. After looking at the brake shoes I decided I should replace them. The frictional material was getting really thin. The auto parts person informed me that I should also buy a rear brake hardware kit, so I did. What is the best method to make sure I get all the springs and clips in the correct position?

A: Your auto parts person was correct. You should replace the hardware when replacing the shoes. One method to make sure you reassemble everything correctly is to remove both rear brake drums and only disassemble one side at a time. Use the other side for reference. If you have a digital camera, take a picture or two on how all the springs and clips are assembled. Use the photos for reference. Also, make sure you have the brake rotors resurfaced before reinstalling.

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Brake Vacuum Booster

Q: When I apply the brakes in the car they hiss. It sounds like a constant flow of air escaping. The brakes are also hard to push. What could be the problem?

A: The brake vacuum booster may be defective. The brake booster works off engine vacuum to give your car power brakes. The hissing sound indicates a possible leak. Without enough vacuum, the power brakes are no longer working as designed. Since driving without power brakes could be hazardous, have the vehicle towed to a qualified service center.

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Brake Sticking

Q: I just had my brake pads and rotors replaced. The right front tire squeaks when I brake. It's been two weeks since the work was done. I wanted to rule out brake dust so I hosed down each wheel after driving a few miles. The right front rotor started steaming when the water hit it.  None of the other rotors did. What could be the problem?

A: Excessive heat on one brake rotor generally means that the brake caliper is sticking. The piston inside the caliper could be sticking or the caliper may not be sliding correctly. When shops replace brake pads they should clean the caliper glides, pins, and bushings. However, some technicians skip this step. After cleaning the caliper glides the technician should put a special lubricant (synthetic caliper lubricant) on the gliding surfaces. The caliper glides, pins, and bushings should be cleaned and new caliper grease applied to enable the caliper to move freely. If the brake caliper piston is stuck, a remanufactured caliper can be purchased. The brake rotor on that side may now be warped and brake pads excessively worn.

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ABS

Q: How do anti-lock braking systems work?

A: Anti-lock braking systems (ABS) use sensors at each wheel (or in the differential) to monitor wheel speed. These sensors can detect whether the wheels are about to lockup. All the ABS components (ABS pump, valve, computer/controller, and sensors) work in conjunction to minimize wheel lockup (skidding) by controlling the brake pressure at each individual wheel. By not locking up wheels, you maintain better control of your vehicle under hard braking conditions and when roads are slippery.

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Brake Pad Squeal

Q: I just had new brake pads installed, but now I hear a squealing noise when I come to a stop. What could be causing the squeal?

A: Brake squeal comes from brake components vibrating. Sometimes new brake pads are made out of a harder semi-metallic material than the original equipment pads. I would always recommend installing OEM (original equipment manufacturer) brake pads or the highest quality that are available. High-quality pads will commonly have the front and back edges of the pad material cut at 45 degrees, which reduces the likelihood of vibration against the rotor. When a technician puts in new pads, the backs of the pads that come in contact with the caliper piston should be coated with an anti-squeal compound or have anti-squeal shims to prevent the metal from the brake caliper piston and the back of the pad from vibrating during braking. Vibration will cause a high-frequency noise. If applicable, anti-rattle clips should be reinstalled and in some cases replaced. In addition, the rotors should be replaced or resurfaced with a non-directional finish to help the new pads wear in properly. The rotors should also be thoroughly cleaned with a brake cleaner before reinstalling. Another component that may have been overlooked is the caliper glide, which moves in and out. When installing new brake pads the caliper glides/pins should be cleaned and new caliper grease applied to enable the caliper to move freely.

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Brake Pad Wear

Q: How long should brake pads last on cars?

A: Brake pad wear depends on the vehicle and how it is driven. A car driven in stop and go traffic is surely going to wear the brakes faster than one that is mostly highway driven. Trucks, SUV’s, and other vehicles that tow trailers will wear brakes faster than average passenger cars. Excessive brake use during mountainous type driving will increase brake wear. On most new vehicles you should be able to get at least 50,000 miles on a set of brake pads. It is not unheard of to get up to 75,000 - 100,000 miles. But again, if you are hard on your brakes by frequently making quick stops you may get substantially less mileage on them.

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Brakes Pulsating

Q: Why does my brake pedal pulsate while applying the brakes?

A: Under heavy braking, you might feel the ABS (Antilock Braking System) working. If you are getting a pulsation under normal braking, your wheel lug nuts may be unevenly tightened. Lug nuts should be evenly tightened using a torque wrench. Look in the owner’s manual for lug nut torque specifications. If you are still getting a pulsation, the brake rotor may be warped. A qualified technician can use a tool called a dial indicator to identify if a brake rotor is warped.

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Brake Rotors

Q: Do brake rotors need to be replaced when replacing the brake pads?

A: Not always. Brake rotors can usually be refinished using a brake lathe. This refinishing process is sometimes called turning the rotors. The technician will measure the thickness of the rotor using a micrometer and determine if the rotor can be refinished. Auto manufacturers list the minimum allowable rotor thickness for each vehicle model. If the rotors are excessively warped or worn to the extent that they cannot be turned, then they must be replaced.

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Brake Squeak

Q: I hear a high-pitched squeak or squeal sound every time I apply my brakes. Why are the brakes on my car producing that annoying sound and what do I need to do to fix it?

A: The squeal that you hear is most likely coming from the wear indicators on your brake pads. A wear indicator is a thin metal strip attached to the brake pad. It is made to squeal against the rotor when the pad wears down as a reminder that it is time to replace your brake pads. To stop the squealing you need to install new brake pads. If you don’t replace the brake pads you will soon hear a grinding noise. This metal on metal grinding will cause damage to your rotors, create a braking hazard, and in the end result in more money to replace.

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