jamesbob02

A week ago, after replacing all 4 of my disc brakes with Performance Friction pads, I soon after developed an annoying squeal from my rear left rotor that only appeared after driving a couple of miles from a cold start, so I had it turned and the squeal went away. Yesterday, the squeal reappeared, so I'm assuming that something caused the rotor to be warped both times, and that turning the rotor again will solve nothing. I've heared that bad braking practices and sudden spot cooling of the rotor (water, etc) can cause warps, but I havent changed the way I drive and I feel that two warps so close together implies something more than coincidence. Since this is the only brake affected and the problem has only occured since I changed to my new PerfFric pads, what can the problem be? Hope you guys can help. Thanks!

AGood2.8

If pads & rotors are not heat cycled when first installed andyou get on them hard with excessive initial heat, then they will warp badly.

Here's the problem- metal has memory, and when you turn a rotor on a brake lath they are cold. Badly warped rotors when turned true at cold temps but then re heated under hard braking will warp back to memory- not as bad as the first time but if not conditioned again and further abused they will warp badly again and again. best to change rotors and start off slowly with proper heat cycling (small increments of heat and then let them cool completely without clamping hot pads in one position.- do this several times before you use them even for normal stops.

Edit; I don't ever get hard on my brakes until I have about a full week of driving and cooling on them even after I do initial heat cycling. Best to run them at freeway temps for a time and cool them.

jamesbob02

Ok I must admit I'm new to the idea of "heat-cycling",which I imagine as just breaking in new rotors or pads, right? I've replaced pads many times without this problem, but that doesn't mean you're wrong at all, I just wonder what I did differently to screw it up this time. If you would, please explain to me the proper way to heat-cycle the pads and rotors without going out and doing normal stops like you were saying.

82camaro

Are you absolutely sure the squeal is from a warped rotor? Maybe just from taking them apart and putting it back together it stops the squeal for a while. I never get rotors turned anymore. They just don't seem to stay 'straight' very long.

lockdude

Disk brakes squeal because of minor vibrations as the pad moves back and forth in it's holder. Anti-squeal pads will reduce the noise. Some brands are louder then others, too. Did you replace the small shims when you replaced the pads? They get old, too. When your rotors are warped, you'll feel the brakes pulse as you stop. Rotors only need to be turned if there are ridges in them. If you turn them too often, you'll have to replace them sooner, 'cause evey time you turn them, you're removing metal. As they get thinner, they get hot faster, and warp easier.

jamesbob02

I know its not a vibration because it happens even when I move as slowly as possible, like idleing with the brake on a little bit - its pretty clear its a rubbing sound that suggests a part on the rotor is misshaped, causing the loud rubbing noise. BTW what are the "shims"?

jamesbob02

I forgot to mention - the rubbing noise cant really be heard until i slow down to probably 25 or less, and it gets louder the slower i get. Also, the sound disappears if I brake hard enough, but its loudest when I'm idling with the brake on a bit and turning the wheels very slowly - its loud and drawn out. What do you think now?

lockdude

That rubbing sound is the vibration I was talking about, and you usually can't hear it at higher speeds or on heavier braking. When you're putting steady pressure on the brakes, do you feel the brakes catching-and-releasing? That would be what you feel if the rotors are truly warped. "shims" might not be the proper term, but there are two-layer metal plates that go between the pads and the piston. They absorb the vibration. There's also a piece of spring-steel that keeps the pad pushed to one side.

jamesbob02

Hmm - I'll have to check that out. However, I am 99% certain that it was warped the first time because it had the symptoms so i took it in - the guy at Oreillys said it would definitely have made that noise and that it was warped, so he turned it and it went away for a week. Thats why I'm assuming its warped again but something is causing it and last time wasnt a fluke.

TomP

Also, think about driving style... if you come off a freeway doing 85 mph and stop in 200 feet and wait with your brakes on at a 5 minute stoplight, for 5 minutes, you're super-heating one area of the rotor with your brakepads. That heat builds up and just sits in one spot. Don't know if it applies in this case (since it's in the rear), but when I come to a stop like that, I try to stop back 5 feet from the light, and just keep inching up every so often; It's my lame attempt at trying to evenly distribute the heat on the rotor. Best bet is not to come screaming up to stop lights, but sometimes, those suckers change at the worst times

jamesbob02

I havent changed my driving style in the 4 years i've been driving, and I've never had this problem before, so I don't think that's it. I see your point, though.

StreetRCR

Your caliper is probably hanging up. Try replacing it. If you drive a while you should notice excesive pad wear on that wheel.

AGood2.8

Your problem is possitively, definately, absolutely warped rotors. I have warped rear rotors twice severly that I had to replace them- tried to turn them even hot (ouch!) and the metal memery still returned from severe overheating of the rotor under very hard braking. Its causes a moaning type vibration noise.

Mine was caused twice from too much rear brake bias- I changed my proportioniong valve and that reduced the excessive heat I was producing in the rear. My brake system is not stock however- I have alter many things for different chassis setup experiments when that happened.

jamesbob02

My brakes are stock 4-wheel disc. Do you think its possible that i have problem with power distribution, like something is wrong with the proportioning valve?

StreetRCR

......and I repeat.........

Hunter Motorsports

Warped rotors.... Here is some great info on "warped rotors"

http://www.stoptech.com/whitepapers/...otors_myth.htm

prockbp

have you thought of the possibility that your axle flange may have been bent and is no longer perpindicular to the axle?

i had an incident where my rear wheel hit a curb moving in a sideways direction and it bent the axle flange... it made the brake on that side squeal...

so my body man put a new axle on and voila, no more brake problems


i'd have to say that the reason it wasn't a problem with the old rotors is because they got worn into the 'groove' of the bent axle(if in fact that is the problem)


anyway, good luck


there is no such thing as 'warped rotors' , only shoddy pads

read this:
http://www.stoptech.com/whitepapers/...otors_myth.htm

AGood2.8

Call it what you want but the simple fact is- you take the frikin rotor off the car and put it on a brake lath and its out of true, then I still say its warped! You need to take material off of it to re-true it.

I have turned many brake rotors in my time and can tell you that when they come up to running/braking temps, the metal has fatigue memory and will go out of round when hot (frikin warped!) and not out of round when cool (frikin not warped!)

Sometime you just have to sh*t can a rotor that has been abused.

Thank you very much.

lockdude

...and when the rotor is warped, you'll feel a pulsing in the pedal as you stop. If you hear a noise, it's something else.
You're welcome very much!

AGood2.8

Did I say I didn't feel it? I think not.

Fact is - I have had the same symptoms in the past that James is discribing- I've offered the solution- Hope he listens- I 'm done with this post.

jamesbob02

Well my dad took a look at the caliper, and it looked like the piston was cockeyed and was putting pressure on the pads unevenly. So we looked at the other rear caliper and dad noticed immediately - the parking brake return spring was off on the one causing the noise, which meant that my parking brake was slightly on all the time, which would cause a moaning at low speeds and slowly turning the wheels but disappear when braked fully. Also, it wouldn't be heard at higher speeds very easily, and wouldnt sound like a moan, and would cause the NEW pads to wear down very quickly. It all makes sense now - thats the way it goes with my car, the least obvious thing is always the solution. If you don't know what I mean by parking brake return spring, its just a spring that puts pressure on the cable that keeps the brake released - thats one of the reasons its so hard to pull the brake lever - that spring is stiff! We had a hell of a time putting it back in place, but now everything is fine! As for the rotor being a little warped in the first place was a huge coincidence, I guess its not warped now and the problem is solved! Therefore, for future reference, be sure and check your parking brake return springs!! Thanks!

lockdude

Glad you got it solved