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mystery noise

T

The Gut

New member
Hey everyone, I drive a 2000 grand prix gt that makes a really irritating thumping noise. I've been trying to identify it for about six months and im completely at a loss. hopefully someone here will be able to point out what I'm missing. Here's the basics.

-i noticed about six months ago. No fender benders or other obvious possible causes.
-definitely coming from front of vehicle somewhere
-thumping starts at about 15mph now. used to start at about 20 mph but has slowly gotten worse
-noise gets louder as vehicle gains speed, then levels off as it hits obnoxious.
-noise goes away completely if i take a right turn with enough speed to lean the vehicle to the left a little
-mostly goes away when i do the same on a left turn.

And this is where it gets mysterious for me lol. heres everything ive replaced in the last six months trying to find the problem. all with new parts and all to no avail. lol though on a bright note, she handles far better then when i got her.:th_thumb-up:

:th_bangheadonwall:both wheel bearings
:th_bangheadonwall:both outer tie rod ends
:th_bangheadonwall:both ball joints
:th_bangheadonwall:both control arms
:th_bangheadonwall:both halfshafts
:th_bangheadonwall:all rotors
:th_bangheadonwall:all brakes (not e-brake yet)
:th_bangheadonwall:all tires
:th_bangheadonwall:both front rims
:th_bangheadonwall:both front swaybar bushings
:th_bangheadonwall:upper radiator support brackets and bushings.
:th_bangheadonwall:engine and transmission mounts
:th_bangheadonwall:all the little rubber hangers on the exhaust

I've exhaustively gone through and looked for anything that could be loose and knocking, though I really don't think thats the cause, as the thump seems to vibrate through the floor. bit intense for something just knocking around i think. replaced the beat up fenderwell splash guards though just on the off chance that they were bouncing off the tires. Im completely at a loss here guys.
 


it do this before all these parts got changed?

can you feel the thud? or just hear it? was it aligned at a shop after the tie rods and lca's?
 
Yea the noise began before i ever put a wrench to the car. Pretty much all those pieces were replaced one at a time, with an alignment done by firestone after each piece (got the unlimited alignment package). they told me my camber is a tiny bit off on the left side, but it was within range. and yes bill, when i replaced the rear rotors and brakes i checked the ebrake. didnt look very worn and i rarely use it so i decided not to replace it.
 


stocker said:
I think strut mounts and/or all new suspension up front should have been much earlier on the list.
Click to expand...
i had the struts checked out by a shop since i dont know how to tell if they are bad or not short of bouncing the front end up and down and checking the rebound lol. shop said they were good. is there anyway i can check them myself that you know of?
 
thats how to test struts, you want to 3 or less full bounces when the car is pushed down and allowed to spring up.

pop your hood, car running, now stand at the d/s door and rock the wheel back and fourth, watch the center bolt in the strut mounts, if they are moving left and right a lot the clunk could be the strut mounts.
 
How many miles on your car or on the current set of struts? If you have the original struts in there, I'd say you are likely due for struts even if they pass the bounce test. Shocks could pass the bounce test while the strut mounts could be worn and making noise.

Clearly you have already dumped a lot of time and money into finding the noise. What is another couple hundred for some quick struts?!

Try Scotty's test and go from there. I was able to see some slight movement/twisting of the center bolt before I replaced my suspension. My chassis is much quieter and tighter with the 4 new KYB quick struts.
 


******* it. its the strut mounts. rubber bushings are both cracked to hell, bolts moves every which way if you so much as think about leaning on the car, lol start rocking it and i cant figure out how the hell its still driveable.... plus i can grab that little metal plate on the very top of the strut mount and rotate it a quarter inch back and forth with minor effort... thank you everyone. once again you've saved the day lol.
 
You don't "have" to, but struts should be replaced every 75k miles anyhow.

I just put a set of quick-struts in from RockAuto, they were a breeze to put in.
 
mounts are like 30 each. then i took my struts out and took them to a front end shop to have them changed. they charged me another 25 or 30. i cant recall anymore lol.

you "need" air tools to change them, and a spring compressor. then theres always the risk of eating a spring in the face, so i dropped them off.
 
Quick struts were the way to go for me. You end up with a whole new assembly (shock, spring, mounts, small parts, etc.) and you can do them all by yourself - just need an alignment when you're done. With all the work you've done, why skimp now?

The ultimate bargain may be to go Scotty's method but there is a lot of time, effort and coordination into the process of rebuilding everything. Not to mention the potential dangers. Also, you could have a shock blow a week later and you're back to square 1.

Best of luck and post up your results!
 


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