pulsating brakes -- and no, the rotors aren't warped! - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-25-2004, 04:53 PM   #1
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Default pulsating brakes -- and no, the rotors aren't warped!

Are there any problems that will emulate the pulsating stops of a warped rotor? I had my pads replaced about three weeks ago, and the rotors looked good, so I declined to have them turned. Ever since there'* been a noticeable grab and release at slow speeds (like crawling up to the line at a stop light) and a vibration at high speeds. I suspected the rotors, and went back up to my friendly neighborhood mechanic to have them double check their work and measure the runout on each of the rotors. I also made sure to brake a little hard on the way there so as to heat up the rotors, hopefully making any warpage more pronounced. Measured runout on each rotor: 0.003", right at spec.

Any other ideas?

-b
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Old 03-25-2004, 05:19 PM   #2
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Did they service the caliper pins?
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Old 03-25-2004, 05:22 PM   #3
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Did they service the caliper pins?
I have no idea what those are -- the service included "cleaning and lubrication of the brake assembly," so read into that what you will.

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Old 03-25-2004, 09:34 PM   #4
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Default Re: pulsating brakes -- and no, the rotors aren't warped!

Quote:
Originally Posted by enmityst
Ever since there'* been a noticeable grab and release at slow speeds (like crawling up to the line at a stop light) and a vibration at high speeds.
The grab and release at slow speed you describe is typical of a drum that is out of round. Of course this will contribute to vibration at higher speeds too while braking, does the steering wheel shake or does it feel like the whole car is whagging around a bit?

As for the rotors, many will say that the rotor should be shaved a couple of thousands just to ensure any previous pad material is removed and just to true them up perfectly. More worrisome may be the process of 'bedding' your pads - some pad material will transfer to the rotor surface and it may have done so in an uneven manner. GM recommends resurfacing the rotors every time the pads are replaced - in this case a surface grinder is preferred over a lathe when it'* only a question of prepping the surface.

Cheers,
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Old 03-25-2004, 09:59 PM   #5
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Make sure the wheels are properly torqued, too tight or too loose is bad for our brakes.
The surging may be from weak brake lines that 'swell' up when the brakes applied as well?
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Old 03-26-2004, 08:24 AM   #6
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Im getting the same condition. The front rotors were $65 each, and only have 6k on them. I inspected them yesterday and no signs of warpage by feeling them. Also, my steering wheel doesnt shake or pull, but the car shakes like a SOB. I think it has the origional drums at 92k, so they have to be it, right?

Jay
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Old 03-26-2004, 11:04 AM   #7
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Quote:
Originally Posted by karfreek
Im getting the same condition. The front rotors were $65 each, and only have 6k on them. I inspected them yesterday and no signs of warpage by feeling them. Also, my steering wheel doesnt shake or pull, but the car shakes like a SOB. I think it has the origional drums at 92k, so they have to be it, right?

Jay
Some people say you feel runout at 0.001", though someone else mentioned the factory tolerance is 0.003". Either way, it'* not something you're going to feel with your hands.

It could well be your drums, they usually have sufficient metal to allow for them being turned so it might be a good thing to at least attempt. If you know the place well where you're going to have it done, I go to the dealer because I know them well and they only charge $12 Cdn each, them ask to make sure they only remove the minimum amount to true them up.

In your case Jay, if you're not feeling it in the steering wheel then it could well be the drums.

Cheers,
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Old 03-26-2004, 12:20 PM   #8
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Quote:
Originally Posted by Foghorn
Quote:
Originally Posted by karfreek
Im getting the same condition. The front rotors were $65 each, and only have 6k on them. I inspected them yesterday and no signs of warpage by feeling them. Also, my steering wheel doesnt shake or pull, but the car shakes like a SOB. I think it has the origional drums at 92k, so they have to be it, right?

Jay
Some people say you feel runout at 0.001", though someone else mentioned the factory tolerance is 0.003". Either way, it'* not something you're going to feel with your hands.

It could well be your drums, they usually have sufficient metal to allow for them being turned so it might be a good thing to at least attempt. If you know the place well where you're going to have it done, I go to the dealer because I know them well and they only charge $12 Cdn each, them ask to make sure they only remove the minimum amount to true them up.

In your case Jay, if you're not feeling it in the steering wheel then it could well be the drums.

Cheers,
Word.

I work in a machine shop, so i can sense surface imperfections pretty well. Im just saying, I could not feel anything too bad. I am going to steal a run out gauge to use over the weekend.

I spoke to my parts guy. He said if after I test the rotors and they come up bad, he will warranty them 100%. Hes the best! He suggested applying the ebrake and seeing if it pulses, guess what im doing at lunch.... New drums are only $25. Sweet!

Jay
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Old 03-26-2004, 03:25 PM   #9
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Quote:
Originally Posted by enmityst
I have no idea what those are -- the service included "cleaning and lubrication of the brake assembly," so read into that what you will.
Blob of grease on a rotor or brake drum, perhaps?
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Old 03-26-2004, 04:54 PM   #10
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yummy!
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