[s-cars] Still Vibrating (long)

[Eric Renneisen]

OK, replaced the subframe mounts and went for a drive... Same
story--vibrates noticeably at 80 mph.  I can feel it in the steering
wheel and through the seat.  I blasted up to 100 and popped the gearbox
into neutral and engaged the clutch; still vibes while coasting with
engine at idle.  That rules out the clutch and flywheel.

To recap, I get vibes when running on the lift with either the center
propshaft removed or the front halfshafts removed.  It's obviously a
rotational imbalance, much like an unbalanced wheel (and I've tried
three different sets of wheels).  All the rubber bits are new.

I'm thinking it's a front diff problem, because the vibes always happen
at the same *indicated* speed.  I'm pretty sure that in the two cases
where I'm running on the lift (nothing on the front and all shafts and
wheels on the back, or nothing on the back and all shafts and wheels on
the front), the TorSen is differentiating because of the different
loads, so the end with nothing connected is spinning faster than the
other.  This means that the front axle is spinning faster without the
front halfshafts, and the rear (TorSen output) is spinning faster when
the propshaft is off.

The speedo reads from the front axle, right?  If so, that says the vibes
are matched to the front axle rotation speed, regardless of the speeds
of the rest of the gearbox and center diff.

Unless someone has other suggestions, I'll be swapping the tranny...

Eric R.
'86 urq
'93 urS


-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com] On Behalf Of Eric Renneisen
Sent: Monday, February 12, 2007 9:34 PM
To: 'jpb3'; s-car-list at audifans.com
Subject: Re: [s-cars] Transmission Vibratons? (long)


OK, after a couple of your suggestions, I decided to take a close look
at the subframe bushings.  For some reason, I was thinking the tranny
mounts tied directly into the body rather than the subframe, even though
I've changed them several times and looked at them every time I searched
for the source of the vibes.  In my mind, the subframe was out of the
picture when I had the halfshafts out, but that's clearly not the case.

So I pulled the rear 'frame mounts.  They seem pretty solid, but upon
closer inspection, they've started to separate:
http://home.comcast.net/~racingiron/Bushing.jpg

Does that look bad enough to cause my problem?  I'm definitely replacing
them either way.  AutohausAZ has Meyle/Corteco for $21 ea, or should I
spring for the dealer parts, or is there a better option (for a street
car--no poly/delrin/alum, thanks).

Thanks for all the suggestions so far,
Eric R.
'86 urq
'93 urS



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