brake fade problem

[street_racer_00]

Lately, I have noticed that my car's brakes have been getting an unusual amount of fade. If I brake moderately anywhere from about 75 mph up, the pedal immediately goes soft and the ABS starts working overtime. This is more likely to occour on hot days, of course, but it even happens during relatively cool nights. For example, last night when I had my little rendevous with the impreza 2.5 RS, I worked the brakes pretty hard only for a period of about 5 or 10 minutes. Then, after about 20 minutes of normal to light brake use, I get home and check the front rotors and they are still too hot to even touch for a fraction of a second, and it takes about 5 or 10 minutes of dousing the rotors with cool water before they finally cool down to just very warm instead of ridiculously hot. Any ideas guys? There is no squeaking or squealing with operation of the brakes either, so I don't think that I need new pads. Thanks.

[LjasonL]

1st of all, don't touch your brakes after you've been driving! They all get hot like that. Throwing enough water on them to cool them quicker than they should could warp them too.

You could try getting some dryer vent, mounting them somewhere in the front of your car where they'll get a lot of air, then mount the ither end to blow in behind the wheels. Hi temp brake fluid could help too.

[street_racer_00]

Whoa, had no idea I could be warping them by doing that, learn something new every day, thanks. Also thanks for the dryer hose idea, I'll look into it.

[Neutrino]

yeah as Idelsyonl said trowing water on them can warp them....heck it might even crack them....


anyway to get beter brake performace i say get a brake upgrade....if you can afford one... the bigger the rotors the faster they'll disipate heat.....it will help greatly if they are vented too....

as a cheaper alternative.....get some better brake pads.....that should give you more stoping power.....also it might be your current pad's fault that it overheats the brakes......maybe to worn or crappy materials

[Volvord 784VC]

First let's clairify the problem, brake fade is when the brake pads reach a temperature where they will not absorb any more heat, brakes work on the simple principle of converting motion energy into heat energy so when the brakes will not transfer any more heat the car will not slow down. When brakes fade your pedal remains hard and firm, but no matter how hard you push on it the vehicle will not slow down because the energy cannot be transformed from motion to heat. Often when brake pads reach these elevated temperatures a gas is released from the friction material which actually "pushes" the pads away from the rotors resulting in the feeling of no brakes at all, but again a very hard pedal. Brakes run at very high temperatures, between 350 - 600+ degrees on passenger cars, up to 900 degrees on competition cars, you cannot touch any part of a brake caliper, pad or rotor for a long time after even a short drive NEVER PUT COLD WATER ON HOT BRAKES, as was mentioned you can warp the rotors and even introduce heat and stress cracks in the rotors.

You say that after short drive the pedal goes soft and the ABS starts to work. I would be looking at 2 potential problems: 1) the ABS is malfunctioning, when an ABS system works it blocks the hydrolic pressure to the brake and then bleeds some of the pressure off to an accumulator, this prevents that brake from locking, this pressure / block / bleed happens multiple times per second (a very simple explanation). The result of this is feeling the ABS "pulse" and the pedal will feel soft as pressure and fluid is routed into the accumulators in the ABS system.

The 2) problem could be as simple as air in the brake hydrolic system, bleed your brakes and give it a try.

Volvord 784VC
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