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Brakes hot? Not to worry

| Saturday, March 29, 2014, 12:01 a.m.

Question: I have a problem with the front brakes on my 2008 Chevrolet Silverado getting really hot. The truck is lowered and has large aftermarket wheels. The truck has 42,000 miles on it, and I put about 70 miles of city driving on it a week.

The other day I came home and took the temps of all four tires, wheels and brakes. The low-profile tire road surface temps were 114 degrees average with the front rotors at 300 degrees and the drum brakes in the back at 98 degrees. The front wheel spokes were warm to the touch, with the area just under the tire reading between 100-120 degrees and at the center hub about 130 degrees. Even when I've put the stock tires and wheels back on, I seem to be getting the same symptoms, including the warm wheels.

The truck brakes fine — no spongy feel or hard-to-brake issues. The steering wheel doesn't shake or wobble when I brake either. How do I determine what's causing the rotors and wheels to get so hot?

— Emilio

Answer: Emilio, I'm assuming you may have used an infrared temperature gun to take these measurements. These are very cool gadgets and provide some useful insight to vehicle functions. I use one to check my trailer brake, bearing hubs and miscellaneous temperatures while on the road. I've found inoperative brakes, a dry U-joint and a binding/overheating brake. I hope not to see bearing hub temperatures much higher than you've noted.

Brakes convert a vehicle's kinetic energy to heat. It is possible, if you know the weight of your brake rotors, to roughly calculate their temperature increase from a single stop, at a certain speed. Multiple stops greatly complicate this exercise.

In your case, I'm not sure 300 degrees is such a bad thing for the brake rotor surface after many starts and stops in city driving. It's best if brake rotor temperature doesn't rise much past this, but under demanding conditions, rotor temperature can rise to double or triple this value. I'd be curious to see what temperature you find after driving for a moderate distance without any stops — perhaps 30 minutes of freeway driving and a gentle coast to a stop. Temperature of the rotor face above about 125 degrees indicates the need for diagnosis. I'd check temperature of both rotors after a single firm stop from 60 mph and see if you are in the ballpark of an on-line brake temperature calculator.

I pondered the possibilities of lowered suspension and kinking of brake hoses; larger tires; a binding caliper; and other braking issues. If both front brakes are similar in temperature and the stock tires provide similar operating results, that rules out most of these possibilities. You mentioned that you haven't encountered any obvious brake pulsation, noise or spongy operation. How does the rotor finish look? Overheated rotors often develop off-colored hard spots.

If your brakes aren't dragging, causing high temperature during non-use driving, the temperature you are noticing may be attributable to normal usage.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies.

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