vibration after brake job

[_J_]

2001 LeSabre, just got new rotors and pads all around.

There's a vibration that seems to come from the rear, but only after driving the car in traffic for some time. When the brakes are cold, there's no vibration.

The vibration seems to be high frequency. I can see the rearview mirror vibrate, but you really can't feel it in the car. The sound is what you notice the most. Sounds like a dog howl. Also, it happens with light braking, when I apply more pressure there's no sound.

Any ideas? I had something similar happen with a Saturn after a brake job and the shop said it was glazed pads. A half hour later, they fixed the problem. On the Buick (different shop), they told me the new rotors on the rear needed to be turned because of run-out.

Turning new rotors seemed like the dumbest thing in the world to do, but I figured 'they know what they are doing'. Apparently not because they didn't fix it.

Now I need some suggestions! Also, anyone think its unreasonable to demand new rear rotors since they probably turned perfectly good ones? Hey, I paid for new rotors, right?

Thanks for any input,

J

[yogi_123rd]

It would be unreasonable to demand new rotors. It is unlikely too that is your problem.

Turning a rotor means putting it on a lathe and chipping it down perfectly flat as a new rotor would be. That process tends to cost less than new rotors so you should have been charged accordingly.

See if your "Dog howl" sound increases/decreases with tire speed. If so, you may have a bad wheel hub/bearing. They do make high frequency whining noise that gets progressively louder as they get worse. You can also find the problem wheel by jacking the wheel up and spinning the tire. The tire should spin true.

[Gocart879]

how about spraying some brake Kleen all over the rotors etc and wipe grease off of them, one fingerprint can cause a lot of squeeks. also i think you should put some miles on the new pads etc, drive around in traffic for a while, then take her up to higher speeds like 65-70 and do some frequent braking. you should see a major improvement.

[_J_]

Thanks for the ideas, although I don't believe its a wheel bearing. The howling made me think of the bearings, but it didn't happen before the brakes were done, and it only happens while the brakes are applied lightly to moderately. The brakes also have to be warm for the howl to appear. No noise, no vibration with cold brakes.

As for new rotors, I paid for new rotors and they installed new rotors. After leaving the shop, the vibration appeared. Their solution was to turn the brand new rotors. If the new rotors were warped, order new rotors, don't turn them. That's the way I see it. I should have taken a minute and thought about it before I let them turn the rotors. I'm no mechanic, but I've worked as an engineer for 10 years and have worked on just about everything with an engine. I definitely don't have the experience of a mechanic nor know all the tricks of the trade, but sometimes common sense helps.

Sorry to rant and rave. I've had the worst luck with Buick service departments. I just moved so I haven't found a good local shop.

Hopefully they'll figure it out when I take the car back in tomorrow. I have done some research, and it seems that these sorts of vibrations are the result of resonance. Sometimes its not even the brakes, but a suspension part that vibrates at the right frequency so that its audible to human hearing.

[HotZ28]

Brake rotors are cast iron. If you have to turn a new rotor, it would have to exceed the specifications for "run -out". Sometimes, just storing a new rotor incorrectly will cause it to warp. Also, if the brake lathe is not up to par or the tool is dull, they will chatter in the lathe and cause a rough cut. A rough cut anywhere on the rotor will cause a moaning sound when you apply the brakes after they warm up.

[_J_]

Thanks for the info HotZ28. The vibration is pretty intense after they warm up and it does sound like a moan, or a howl.

[_J_]

New pads did the trick. Like I mentioned earlier with my Saturn, I believe the pads got glazed.

The tech tried cleaning the pads and turned the rotors, but it took brand new pads to solve the problem.

[HotZ28]

You said in the first post that you just had new pads and rotors installed. If they glazed that quickly, you must either be hard on brakes or did not follow the break in procedure. Some people are so happy to have all new brakes installed, that they take it for a high speed driving and stopping exercise. That is the worst thing you can do to OEM type brakes. Drive it slower than normal, and let them cool off more often during the break-in process (about 200 miles).

[_J_]

I drive slower than normal all the time! There's always a huge gap between me and the car in front of me, and I always brake early and gently. I'm getting old, must be why I have a Buick!

I understand your comment, HotZ28, but me being hard on the brakes is not the right assumption. Maybe when I first got my driver's license it would have been accurate! My standard break-in is 'one full-tank of gas'. That's usually 300-400mi, no matter what car. And, my fiancee did not drive the car or else I would have accused her of being hard on the brakes! Hey, maybe it was the tech that was trying to 'set' the pads for all I know.

BTW, this situation has only happened twice. Once with the Buick and once with the Saturn. I've changed my own pads many times before and never experienced this. I've also gotten new pads/rotors from dealers/shops and never had a problem. If I had my own garage/driveway I would not be paying someone to work on my brakes. I generally don't trust 'all' products off the shelf, either. Brake pads, like anything else can be defective. And, guess what? The brake resevoir was overfilled! I think it got 'topped off' somewhere along the way, but any time you work on the brakes you should always check the resevoir. I pulled 40cc out of the resevoir.

Now, as for the dealership, those guys were helpful, friendly and owned-up to the problem. Yes, I was annoyed to have to re-visit them (and they didn't notice the resevoir being over-filled), but they did fix the problem and it was a learning experience, I think, for everyone. The tech was a younger guy and he will know where to start if this sort of thing happens again. Their attitude was refreshing compared to other dealers I've dealt with.

Thanks for the feedback everyone.