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Old 10-08-2008, 10:22 PM
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Daily Driver thumping when breaking

car: 2005 Pontiac bonneville

When slowing down from any speed there is a thumping feeling through the break pedal and seat, coming from the front end. Thumping is more violent with greater break pressure and the interval of thumping coordinates with speed (more thumping at highers speeds) the car does not pull to either side when breaking, and other than this thumping the car operates normaly

I thought this was a classic case of warped rotors, so I replaced them and pads and it made no difference. Next I replaced the front tires, they were old and I figured maybe a belt shifted, still no fix. Just today I replaced the front transmission mount, still no fix.

I have looked at the tie rods ends coming off the rack and they feel fine along with the lower ball joints. No movement though the joints when I push/pull/jerk on suspension. I have also snugged up all of the strut bolts.

Just tonight I lifted up the front end on jack stands and brought the car up to about ~30mph everything seemed fine. Then I applied the brake when giving it gas, trying to simulate a ~30 heavy breaking and thats when the whole cars started to bounce, vibrating quite a bit.

This leads me to believe the problem is in the break system and not the suspension or drivetrain. The only thing left that is not brand new are the calipers.

Any help or suggestions would be great!

thanks, Matt

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Old 10-08-2008, 10:32 PM
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Possibly the wheels are bent but that should have been caught when the tires were balanced - you did get the tires balanced.

Another possiblity would be loose or bad front wheel bearings.

Possibly the ABS system is not working correctly.
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Old 10-08-2008, 11:06 PM
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Several things come to mind.

First, and foremost. If there was any rust on the front hubs, did you clean it off?
Next: Are the caliper slides free? Easy to push in and out.

Next: Is there any ware to the disc BRAKE(take note of spelling) pad mounting/caliper mount bracket?

Lastly: Where did you purchase the brake parts?
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Old 10-09-2008, 06:50 AM
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Wheels were balanced and visually spin true

I have pulled the abs fuse and the problem is still there

Parts are all form NAPA, so I feel they are ok

Everything was quite clean when I installed it. I am gonna completly disassemble the brakes and really look it over and put it back together, maybe I missed something.

thanks, matt
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Old 10-09-2008, 07:00 AM
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Is it anti-lock? Could be in that system.
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Old 10-09-2008, 07:40 AM
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Make sure the caliper is tight and not interfering with the wheel and that the rotors are seated properly against the hub. Then I would disconnect the battery for 5 minutes to reset all the codes for the abs.
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Old 10-09-2008, 10:26 AM
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brake problem

Have you checked the drive shafts for loose knuckles? Torn or missing boots etc mean trouble.
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Old 10-09-2008, 11:16 AM
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I have had many I mean MANNNNNYYYY warped rotors out of the new box. I would not rule out warped rotors just because they are new.

Is the problem only present during braking?

Do you feel it in the seat or in the steering wheel?

A rotor can warp by just torquing the wheel nuts too tight.

Steve
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Old 10-09-2008, 11:21 AM
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When did it start?
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Old 10-11-2008, 12:57 PM
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I took the brakes apart today cleaned everything again and setup a dial indicator.

First I measured both hubs, with the dial indicator securly mounted to the spindle, both hubs read at most .0005". Next I bolted on the rotors with all five lugs snug. Driver side rotor showed a high spot of about .0005" and the passenger side showed a spot of all most .001". This leads me to believe the rotors and hubs are fine.

Questions:

10-09-2008 05:21 PM
redlightning When did it start?

Probibly about a 6 months ago, Its my mothers car so I have not been around since the begining, but I have known about it since early spring

10-09-2008 04:26 PM
Gringo Have you checked the drive shafts for loose knuckles? Torn or missing boots etc mean trouble.

Both half shafts boots look fine, there is a small amount of end play in the shaft (not the hub bearing) and a small amount of free play when rotating forward and backwards, but I am assuming this is normal for a FWD car.



I am gonna clean and reassemble everything tonight and take it out of a drive later, see if anything has changed. Think I might try some 40-0 stops with the trans in neutral just to rule out the tranny. Only thing I can think of is the hub bearings. I don't know it just doesn't make sense. It feels like warped rotors, at higher speeds the vibration/thumping can be felt through the brake pedal and the seat (not really the steering wheel) and as you approach a dead stop you can still just barley feel the thump.
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Old 10-11-2008, 01:50 PM
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Have you inspected the rear brakes?

And tires



R
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Old 10-11-2008, 02:08 PM
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Are the mounting surfaces of the hubs clean, if not the sand blast them.
Did you torque the wheels. Improper torque can destroy a set of rotors.
Did you check for run out on both the front and back of the rotors. We have seen where the front and back will read different on slotted rotors, especially the cheap ones.

Chet
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Old 10-14-2008, 06:15 PM
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Quote:
Originally Posted by Blob
I took the brakes apart today cleaned everything again and setup a dial indicator.

First I measured both hubs, with the dial indicator securly mounted to the spindle, both hubs read at most .0005". Next I bolted on the rotors with all five lugs snug. Driver side rotor showed a high spot of about .0005" and the passenger side showed a spot of all most .001". This leads me to believe the rotors and hubs are fine.

Questions:

10-09-2008 05:21 PM
redlightning When did it start?

Probibly about a 6 months ago, Its my mothers car so I have not been around since the begining, but I have known about it since early spring

10-09-2008 04:26 PM
Gringo Have you checked the drive shafts for loose knuckles? Torn or missing boots etc mean trouble.

Both half shafts boots look fine, there is a small amount of end play in the shaft (not the hub bearing) and a small amount of free play when rotating forward and backwards, but I am assuming this is normal for a FWD car.



I am gonna clean and reassemble everything tonight and take it out of a drive later, see if anything has changed. Think I might try some 40-0 stops with the trans in neutral just to rule out the tranny. Only thing I can think of is the hub bearings. I don't know it just doesn't make sense. It feels like warped rotors, at higher speeds the vibration/thumping can be felt through the brake pedal and the seat (not really the steering wheel) and as you approach a dead stop you can still just barley feel the thump.

Double check all of the engine, and under carriage bushings. You could be chasing the wrong thing, with the brakes.
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Old 10-14-2008, 07:08 PM
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On the weird side might be a Locking...Not UN locking torque converter not disengaging.




R
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  #15 (permalink)  
Old 10-14-2008, 07:48 PM
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Quote:
Originally Posted by Rob Keller
On the weird side might be a Locking...Not UN locking torque converter not disengaging.




R
That is not on the "weird side" Rob.

The explanation of the brake inspection, and the "feel" in the vehicle, and not in the the steering wheel, opens up a lot of other possibilities.

I would not rule this out, because torque converters do not lock up until between 25 and 45 MPH. They can cause a "shudder".
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