Brake shake with freshly machined rotors?

Hi all,

got a bit of a puzzlement. Ever since I've had it, my '08 Impala has had a pronounced steering shimmy under braking - the harder you brake, the more the wheel shakes back and forth.

I finally took it in for its first service in my care today, and asked them to balance and rotate the tires and also to turn the front rotors. I ASSumed that this would take care of the issue (the tire balance was because I was also having a shake at highway speed, not to address this problem) but it did not - it's still doing it, and almost as badly as it was before. The rotors show clear signs of having recently been machined; there's obviously marks in the iron that are not circumferential (I'm guessing they must have dressed it with a sanding disc or similar while spinning on the brake lathe after turning) so it doesn't appear to be a halfassed job on the part of the shop.

I'd suspected that the cause of this issue was because the car sat for several months unused before I started driving it, so I just ASSumed that the brake shake was due to rust buildup on the rotors (except of course where the pads had sat, causing the rotors to wear unevenly when the car was put back in service.) Of course, I suspect that also the rotors are undersized for the weight of the car, but that's typical, and if it were simply warping, wouldn't it take a while to reappear after machining?

Any ideas as to why this could be?

nate

Reply to
Nate Nagel
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Maybe you have a shimmy that is unrelated to the actual braking system. Checked the tie rods? All the bushings? Get under there and start tugging on stuff and seeing if you can feel any play in anything in the front end.

--scott

Reply to
Scott Dorsey

Car has only 21K miles on it (about 4K of which are mine) it'd be pretty pathetic if it had worn out suspension components already.

I didn't mention that it had a slow leak when I first got it and I'd noticed that the steering wheel was slightly off center, so when I left it to have the tire plugged I told them to check/correct the alignment. One would think that that would involve doing all that you suggest.

nate

Reply to
Nate Nagel

My guess would be a bad tire. Did they rotate them? It could also be a sticking caliper, but then you would probably feel it in the brake pedal also.

-jim

Reply to
jim

FWIW, If I intentionally brake heavy several times the pulsing problem gets better and sometimes disappears. The rotors were still in specs after being turned, but I think you may be right in thinking that they are under engineered.

You didn't say how many miles is on the car, but the suspension is the only thing I can think of that would cause the the highway shimmy. More specific, the front shocks or struts, which ever it has.

I had a '93 S-10 that had bad bushings in the front A frame. It caused the truck to veer to one side or the other under hard braking. There was also a loud clunking sound when braking some times. It also exibited some weird symptoms going down the highway. Sometimes, but not always, the truck would get the shimmys after hitting a pot hole or going over a bump. That all ws corrected when the bushins were replaced.

Reply to
Anyolmouse

Yes, the tires were supposedly both balanced and rotated, and I know the tires are bad. They're Goodyear Integrity, the same crap tires that were on my last car. Unfortunately there's not much I can do about that unless I want to pay for new ones out of my pocket.

nate

Reply to
Nate Nagel

good point. maybe I will loosen/retorque lug nuts myself and see if that helps.

nate

Reply to
Nate Nagel

There could be hard spots on the rotors. And perhaps while it was sitting the area where the calipers were that did not rust is now either harder or softer then the rest of it from that, although I would not give that high odds. I had a impala back in the 70's that did what you were describing and they only fix that worked was new rotors.

Reply to
Ashton Crusher

Those things dont always work they way they should. I have had two sets of rotors warped because of them.

Reply to
HLS

It's worth a try, but I doubt it will help..

As said before, tires are a possibility, bad machine work is another, and tire/rotor reinstallation (on some models) is a third.

I had some rotors cut once and when I remounted them on the GM product, you could SEE the wobble. The machinist didnt set up the lathe correctly.

If you dont still have the Coxco (?) link, let me know and I will find it for you.

Reply to
HLS

I have done that on my explorer and it did help.

Reply to
Ashton Crusher

Just a suggestion: when you take a car in for warranty work, never ever tell them 'how' to fix it. When you suggest a repair technique, that is what the do, nothing else, because that is what you asked for. Instead, give them the symptoms, make sure they can duplicate these symptions and say: "Fix it, warranty". Heck, even if it is not warranty, don't suggest how to repair a fault! People make this mistake over and over--the shop must do what you suggest even if they know it won't fix the problem, and they cannot fix anything else because you asked for a specific action to be performed.

Never assume. Let the shop/mechanic find teh problem.

Well, first, a warranty repair should be done ASAP after the flaw is noticed. Don't wait for other problems to appear. Second, don't assume what is causing a problem. Now the dealer can say the did what you asked, and will be reluctant to do more.

Possibly bad rotors, as you suspect. They could easily be warped, or have excessive runout. Can't say until diagnostics are performed.

Reply to
PeterD

Steering Wheel Pull/Shimmy When Braking PROBABLE CAUSE: REMEDY Uneven braking force: Check for mechanical or hydraulic problem. Inoperative brake: Check for seized caliper, fluid leak or restriction, worn or contaminated lining. Weak or broken spring: Replace spring. Worn shocks or struts: Replace struts or shocks Deteriorated suspension bushings (especially control arm pivot): Replace bushings. Loose wheel bearings: Adjust or replace bearings. Excessive disc brake rotor run-out: Replace both front or rear brake discs or rotors. Improper front wheel alignment settings: Adjust alignment to factory specifications.

(From

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--Vic

Reply to
Vic Smith

And when you do tell them you want something, ALWALYS get a price. I learned that the hard way....I asked them to replace the brake retainers figuring they couldn't be more then a couple bucks each. When I got the bill I was about to call for the manager to figure out why it was $70 higher then I expected till I saw what they price was for the brake retainers......

When you suggest a repair technique,

Reply to
Ashton Crusher

Nate Nagel wrote in news: snipped-for-privacy@news1.newsguy.com:

Of maybe some help:

Did anybody make certain the tires spun ABSOLUTELY true with NO hop, wobble or snaking BEFORE balancing was attempted?

ANYthing but dead-true will result in unsatisfactory performance. And those much-vaunted Hunter road-force machines tend to cover up or disguise inept mounting, so they're not much of an answer.

I've had many years of tire replacements on several cars as personal experience in this matter, many of those replacments being followed by highly inconvenient and annoying multiple re-visits to the garage that did the work in an attempt to get them to fix the vibration, which they rarely could.

I finally gave up and asked my mechanic if he could install tires for me. he said sure. What a difference. So far, glass-smooth EVERY time. Even though his "bedside manner" isn't that great, I worked up the nerve to ask him why he was able to do this and nobody else appears to be able to. He explained the problem in great detail, and showed me physical evidence of why so many places have problems with comebacks due to vibration, using my own tires (mounted by somebody else) as one example.

The upshot? Basically, inept technique. Mounting tires properly is not difficult at all, but does require some very basic knowledge of some very simple things. Problem is, most tire monkeys receive little training, and their bosses understand little to begin with.

Reply to
Tegger

I can't answer this question (see below)

You just described the exact problem that was driving me nuts on my 944 for literally years until I found a local Porsche club guy who had his own tire machine.

However I have yet to report success because both my rim and tire exhibited runout and I haven't had a chance to swap the tire (on a straight rim) back on the car to see if it is acceptable or if I need another new tire.

But back to the problem at hand, I am limited to two repair shops for work on this car unless I want to pay for the work myself (fleet car) so it may simply remain unresolved, much as it bothers me (I know it can't be good for ball joints, tie rod ends, etc.) Or if I end up with a windfall sometime soon, I may take it to a GOOD shop and just point and say "fix."

nate

Reply to
Nate Nagel

You can machine warped rotors all you like, but it will not make any difference as far as the warping is concerned. The lathe will just follow the warp in the rotor and cut it the same, only thinner. Sounds like you need a new set of rotors. I would check the rear brakes to make sure they are operating as well, usually warped rotors result from either too much effort on the part of the front brakes trying to stop the car (excessive heat), or a mechanic overtorquing the wheel nuts upon reinstallation and unintentionally causing the warpage in the rotors.

How much pad lining is left on the front pads? Did they re-use the original pads, or install new ones? When they re-installed the caliper sliding pins, did they clean and then grease the pins and sliders so that the caliper slides freely?

Just my 2 cents, Sharky

Reply to
Sharky

Absolute caca.. If you do it right, you can definitely machine the rotors, and if you reinstall correctly this can last a long time.

I suspect you had some bad experiences, Sharky.

Reply to
HLS

50-75% pad left, original pads, and no idea if they lubed it. If I'd done it myself I'd have lubed it, but I don't feel like working on company car myself. I did change the oil when I first got it because it was due on time but not on mileage (so I couldn't get them to pay for it) and I was so paranoid, even though I've never screwed up an oil change in my life.

nate

Reply to
Nate Nagel

Nate Nagel wrote in news: snipped-for-privacy@news1.newsguy.com:

balance was

ASSumed

typical, and

One of your tires is bad. Check for bumps or imperfections in the sidewalls.

Reply to
JJ

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