Clunks

["Al Powell" <APOWELL@agcom.tamu.edu>]

Well, I'm still chasing clunks in the front end of my 1990 200.  
I have been trying to get some actual clue as to what's going 
on before changing parts on sheer speculation.

Known items:

1)  Upper strut bushings are OK; I removed and inspected them.
2)  Sway bar bushings on ends are not *visibly* damaged or degraded.
3)  Center sway bar bushings do not appear to be loose or damaged.
4)  Visual inspection of the left inner control arm bushing shows one 
small crack in the rubber.  That's it.
5)  Both front sub-frame bushings have been replaced by me.
6)  Both transmission (rear) rubber mounts have been replaced by me.

The car has clunked for some time with turning right, then hard left. 
It also gradually has begun to clunk slightly EVERY time weight is 
transferred to the rear of the car (under acceleration), followed by 
braking.  In other words, at each stop, there is a definite clunk.

Yesterday, it started to make a grating, scraping sound as well.  
This happened after the car had been immobile for about two weeks 
while the timing belt exercise went on.

After about 20 minutes' driving, the grating sound diminished quite a 
bit.  But it sounded almost like a broken shock, because EVERY time 
that LF corner went up and down, it grated and clunked audibly.  I 
took the car home and had my wife bounce the front up and down while 
I looked and felt underneath the front end.  The ONLY vibration I 
could feel was on the RIGHT lower control arm.  It seemed to be 
stronger toward the inner side of the arm, near the inner bushing.  I 
could detect no noise or leakage from either front shock.

Inspiration struck!

I took a can of spray silicone and sprayed the WHEE out of both inner 
control arm bushings.  I really soaked 'em as well as I could.  I 
also sprayed the bushings at the end of the sway bar.  Then I went 
out for a drive.

Scraping and grating noise:  GONE.  Clunk: still present, but 
less audible.  I can definitely make the front end clunk *every time* 
I stop, accelerate enough to bring the nose up, then brake.

Perhaps this seems elementary to others, but this has been really 
hard to track down far enough that I'm willing to spend the money on 
4+ hours of labor to change the control arm bushings.

My deductions so far:

1)  It's NOT strut bearings, as this happens even if the 
steering wheel is not turned.
2)  It's not the shocks, as I would have heard it while bouncing the 
car.
3)  At least part of the problem **MUST BE** inner control arm 
bushings, as spraying them did produce an audible change.
4)  I might as well go ahead and have the control arm bushings 
changed; while I'm at it, I will have the outer sway bar bushings 
changed, as they must come off anyway.

I plan on dropping it off at my mechanic's this weekend, and asking 
him to drive it Monday, then install the bushings unless he can find 
evidence of a different problem.

Anyone have  a different concluion which fits the facts?

I appreciate your well-reasoned comments.....


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Al Powell, Ph.D.                 Voice:  409/845-2807
107 Reed McDonald Bldg.          Fax:    409/862-1202
College Station, TX 77843      
Http://agcomwww.tamu.edu/agcom/satellit/alpage.htm
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