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grand prix brake shudder

Posted by joe_mn (My Page) on
Mon, Jun 29, 09 at 10:08

99 grand prix gt. front end shudder when using brakes. seems very pronounced. I know brake vibration is fairly common on GM cars. i have done many brake jobs and know putting on a new set of rotors is easy/quick. not much $$ either. less than having a shop even look at the car would cost. dogbones or engine torque straps look ok. no obvious bushing distortion. no vibration on acceleration. axle shafts/cv joints are ok? put car in gear and have someone observe motor movement? any ideas?


Follow-Up Postings:

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RE: grand prix brake shudder

Very likely, the rotors need truing or replaced, the pads are probably worn out, and the calipers may be sticking on the pins.


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RE: grand prix brake shudder

Most likely warped rotors. You should do a complete brake inspection and repair as needed though rather than focus on one thing though.

Side note. Not all rotors are created equal. Brand new rotors for your car might cost $80 a pair or $200+ a pair depending on how good you want them to be. If you've had repeated problems with the stock ($80) rotors, you might want to spend the money and upgrade to the better slotted and/or cross drilled type. jmo


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RE: grand prix brake shudder

found a set of new raybestos rotors on CL for $25. I have 2 cars that need rotors though. 1 car has worn rotors and stops fine while the other looks to be in better shape but vibrates.


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RE: grand prix brake shudder

From the "anybody can do brakes file".

Brake pulsation (shudder) has two primary causes, but a lot of subplots. Basically its either rotor run-out, or rotor thickness variation.

Rotor run-out can be caused by the classic idea of a warped rotor, however it can also be caused by a bent wheel hub, rust jacking, improperly torqued wheel nuts etc. Rotor thickness variation, also know as parallelism is caused by runout, rust pitting, surface delamination, and unbalanced pad material transfer. I don't have time to teach a brake class here but replacing, or machining the rotors is only one step. You have to measure and correct for runout or else the pulsation will come back in a few thousand miles. (or less)


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RE: grand prix brake shudder

Yes, but 99% of the time it's a warped rotor, especially on cheeper GM cars. Sticking calipers and slapping the wheels on unevenly with an air wrench will certainly do it. Also, observing the caliper and turning or replacing the rotors is all 99% of shops will do if you pay them for it. I'd bet a high percentage of those will screw it up again while putting the wheels back on.

FWIW, I drive a 2008 HHR that's had this problem for 10k miles already. It has 27k on it now. They're notorious for this problem, and I knew about it before I bought it. Knowing that, I'll not get huffy and insist GM fix it under warranty over and over again. I'll just buy better rotors, install them myself and be done with it.

Last time I paid a shop (all ase certified mechanics) to do something for me was to replace the heater core in our '98 durango. Air out the vents has been reduced to zero on the right side, 25% in the center, and to 75% on the left side. In other words, they screwed something up. At least the driver has almost enough cool air blowing out to be comfortable. Another job I'll have to fix myself that I already paid someone to do. Happens way to often...at least to me. IF we ever get our house sold, and a new one built, and my new shop built, the Durango is going on the rack to be gone through stem to stern by me. I'll pay someone to do the alignment and purge and recharge the ac when I'm done. That's about it.


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RE: grand prix brake shudder

Do you want to actually talk about why this happens?

Quote"
Also, observing the caliper and turning or replacing the rotors is all 99% of shops will do if you pay them for it. I'd bet a high percentage of those will screw it up again while putting the wheels back on. "

There is a cost for trying to be too cheap, and sure I'll get all kinds of responses where everyone will want to point out how expensive they are sure a shop is, but the facts are that is exactly how pressure has been applied to shops and techs for decades, and has forced auto repair to be artificially under-priced. In short, everyone tries to go too fast and be cheaper than the other guy, and eventually something (quality) has to suffer.

Quote"
Last time I paid a shop (all ase certified mechanics) to do something for me was to replace the heater core in our '98 durango. Air out the vents has been reduced to zero on the right side, 25% in the center, and to 75% on the left side. In other words, they screwed something up.

Was the problem evident right away, and did you go back?
Having done several AC/heater repairs on these I can tell you that something doesn't add up and I would have to see this myself in order to get to understand the symptom as you have reported it. Another thing, ASE certification is a start, but to truly be able to work fully with today's cars requires tons of continuing education, and an ever growing expense in equipment. Which again is part of the problem where everyone tries to be too cheap. The shop might have one true master tech, that everyone else has to rely on when problems occur. However did you know there are more lawyers in the state of New Jersey, then there are ASE CMATs in the entire country?
Today there are between 600 and 700 registered cars on the street for every CMAT. That number is going to get uglier as my generation retires in the next ten years because the 50+ group makes up more than 70% of the CMATs!

Quote" IF we ever get our house sold, and a new one built, and my new shop built, the Durango is going on the rack to be gone through stem to stern by me."

If your that capable, instead of building a house that I can't understand the need for, why don't you build a shop, hire AND train techs to work to your high standards and show the rest of us how it should be done. If your as good as you imply you should be able to make a fortune. (sarc*)

BTW, prior to doing any brake repairs, one should pull the calipers and gently tighten two wheel nuts, and install a dial indicator and measure the run-out on both sides of the rotor. Mark the high spot on the rotor, and where that high spot is on the hub. Now when the rotor is moved to the lathe, ensure whether the high spot marked on the rotor while it was on the car is still the high spot now that its mounted on the lathe. If it is, your probably good to go, if its not then you need to find and correct for the run-out at the wheel hub assembly. Sometimes that can be as simple as re-indexing the rotor when you put it back on. Other cases require shims that go between the rotor and the hub, or machine the rotor on the car which automatically corrects for run-out. This is what HAS to be done to correct your HHR's issue. Unfortunately, flat rate techs aren't paid to take steps like this, because as you said, some 99% of the time all they do is simply slap on a new rotor, or machine it off the car and stick it back on the car and that is sufficient to solve the problem. But the one time that it isn't we get to see complaints just like yours, its only then that the car moves to the more experienced technician.

If you see a tech that measures rotor run-out when assembling every car, you have one who will be slower than average, but have fewer comebacks which means, you should and will pay more than average for his/her work. You cannot call the shop and ask "how much is XXXXXX" first and find them.


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RE: grand prix brake shudder

*Was the problem evident right away, and did you go back?
Having done several AC/heater repairs on these I can tell you that something doesn't add up and I would have to see this myself in order to get to understand the symptom as you have reported it.*

Yes, the problem was evident right away...which is why they shouldn't have returned it to me that way. I started a new job 150 miles away from this shop. Though the wife was still in our same house, and she drives this car, the shop was in the town I previously worked in some 30 miles away, and we had no spare vehicles. It's just unfortunate for us this time. They've done good work for me before.

The ducts are a single assembly attached to the dash, which comes out in one large piece...after removing the steering column...and the kick panels...and the door sills...and the 'A' piller plastic. The heater/AC unit is attached to the fire wall. I assume when they placed the dash assembly back in place, they lined up with the duct on the left, missed most of the duct in the center, and totally missed the one on the right. The blend doors seem to still be working. I'm sure they would have fixed it if I could have brought it back.

Here's another one. Water pump in my '87 corvette failed on my way to work on a storm day. I work for an electric utility so when a storm hits, my shift goes 36 hours on or so to start with, then 8 off, 16 on, and so on untill most everyone's lights are back on. Being exhausted, I limped the car into another shop which replaced the water pump. A few months later, I'm loosing coolant again on the left side. I rip and tare on that side and find the water pump leaking where it bolts to the block. I tighten the bolts...no more leak. A couple months later same thing, only on the other side. So, I rip and tare that side apart and find the same thing. Tighten those bolts and no more leaks since. What did I pay $600 for? For what I had to do later, I might as well done the whole thing myself the first time. There's been others.

**If you see a tech that measures rotor run-out when assembling every car, you have one who will be slower than average, but have fewer comebacks which means, you should and will pay more than average for his/her work.**

I've never seen any tech anywhere do this. I'm sure they're all getting paid on commission based on flat rate so it pays to be fast and good enough, not so much to be 100% accurate. I'm pretty sure the rotors on my HHR weren't good enough to begin with. To many other people with the same complaint.

If your shop was in my town, I'd ask you to work on my vehicles.


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RE: grand prix brake shudder

both rotors had excessive wear and grooves on the inside surface. is that a result of the calipers not sliding on the guide pins properly? after years of salt spray and MN winters, the rotors can get pretty ugly. i checked that both rotor mounting surfaces on the bearings was nice and clean and rust free. stops much smoother now. i did not check for runout as i do not have a dial indicator. but i will be at my dads this weekend and he does have one.


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