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The mechanics of how disc brakes function haven’t changed much for a long, long time. Sometimes, at Tire Central and Service, we run across customers who 

have some misconceptions about how they work, or about “innovations” in brake design that aren’t really worth it. Here, we’d like to clear up some of those myths:

Q: I see sports sedans and coupes from time to time with holes drilled through the rotors. Is there an advantage to this?

A: Really…no. The idea of drilled rotors is to (in concept, at least) provide better ventilation and disperse heat. In practice, though, those evenly-spaced holes in the face of the rotor really just mean dozens of weak points in the material. Any metal will expand when heated and contract when it cools, and over time the rotor face will start to develop a network of cracks, all of them starting at the holes. Brake rotors are already designed with cooling vanes between the front and back faces of the rotor; holes really don’t do much other than compromise the integrity of the iron.

 

Q: My car’s developed a pretty noticeable pulsation that can be felt through the brake pedal. Are my rotors warped?

A:  Maybe so, maybe no. The surface of brake rotor is hardened cast-iron that can hold up to years of heat/cool cycles and tens of thousands of miles of wear. Still, the surface of rotors can wear down to the point of needing replacement. What’s more likely than a warped rotor, though, is “hot spots” of brake pad residue left on the rotor, causing a slight irregularity in the rotor’s thickness. At one time, shops would routinely resurface a worn rotor in the machine shop. Today, the cost of rotors has come down to a point where it makes about as much sense to just replace a worn rotor with a new pair (yes, always replace them in pairs).

Q: My brakes start to seem less effective after I’ve been driving in hilly terrain. Do I need to replace my pads?

A: “Brake fade” isn’t a problem with the pads or mechanical parts. It’s a problem with the brake fluid itself. Brake fluid is formulated for a high boiling point and a lack of compressibility, which it needs to deliver hydraulic pressure from the master cylinder to the wheel cylinders when you step on the brakes. Brake fluid is very hygroscopic, however – it attracts and retains water, even if only in droplets. All it takes is about three percent contamination from water to lower the boiling point of brake fluid by about 150 degrees. When that water is boiled off after severe usage and heat, it leaves tiny air bubbles in the brake lines…which is what causes that fade and a ‘spongy’ feel to the brake pedal.

Q: My brakes are noisy --- they sometimes squeal or groan when I step on the brake pedal. Is it time to replace the pads?

A: Not necessarily. Remember that any noise is the result of vibration, and sometimes noisy brakes are just vibrating as they catch and release thousands of times per second on the smooth steel face of the rotor. Here, it’s worth noting that all brake pad friction materials differ. Some are composites of semimetallic fibers, others are ceramic-based; some tend to make noise right after they’re installed, until the brake pads are “bedded” and broken in properly. The good news is, this is a fairly easy problem to fix. Shims of Teflon material are available to mount on the backing plate and help damp that vibration. Sometimes, even a coating of special high-temperature grease can be enough to quiet things down again. When it comes time to replace pads, it’s generally a good idea to go with factory-quality pads that meet the friction specs of the original equipment your vehicle was designed with.

A word of caution, though. Many brake pads feature a spring-steel finger that protrude from the backing plate and serves as a wear indicator. If your pads’ friction material wear down to a minimum thickness, this steel tab will drag on the brake rotors, setting up an unmistakable metallic screech that sounds completely different from the squeal or groan that you’re used to.

 

Got any more questions for us? Give us a call and make an appointment at Tire Central and Service in Indianapolis, IN! 

A Few Myths About Brake Repair was written by Mat Johnson of Tire Central and Service