[s-cars] Transmission Vibratons? (long)

[calvinlc at earthlink.net]

Why don't you have another person run up the speed without the shafts on and
then feel the tranny/engine directly for the vibrations.  My first suspicion
would be the driveshaft....40 mph is either classic "U-joint" or driveshaft
territory on older RWD cars.
--Calvin


-----Original Message-----
From: s-car-list-bounces at audifans.com
[mailto:s-car-list-bounces at audifans.com]On Behalf Of Eric Renneisen
Sent: Sunday, February 11, 2007 7:17 PM
To: 'chris chambers'; s-car-list at audifans.com
Subject: Re: [s-cars] Transmission Vibratons? (long)


Engine mounts are new.  Transmission mounts were new aftermarket, but I
found that the mounts that came with the low mileage 6-speed provided
more support than the crappy Chinese new ones.  Vibes are present with
either installed.  Subframe mounts are original, but seem to be fine--no
obvious wackiness there.  Are there any specific checks for the subframe
mounts?

If any of those mounts were at fault, I should certainly get the vibes
with none of the shafts installed, right?  My thinking is that the good
motor and tranny mounts soak up all the vibes, but the shafts provide a
path for the vibes into the rest of the car.

Thanks,
Eric R.
'86 urq
'93 S4

-----Original Message-----
From: chris chambers [mailto:fastscirocco_2000 at yahoo.com]
Sent: Sunday, February 11, 2007 8:31 PM
To: Eric Renneisen; s-car-list at audifans.com
Subject: Re: [s-cars] Transmission Vibratons? (long)


Eric,

I don't believe you have proven the trans is at fault, if it was the
trans the vibes would be there all the time.

What you have done is proven that you get vibration whenever the
propshaft or halfshafts are installed.

What is the condition of your engine/trans/sub-frame mouunts?

Chris



--- Eric Renneisen <racingiron at comcast.net> wrote:

> Patient is a '93 S4 with 170K miles on the clock.  I'll try and
> condense the history of this problem a bit, but it's still gonna be
> long:
>
> Last year the car was all stock, including original suspension bits.
> At
> highway speeds I'd get a nasty tank-slapper (violent oscillations in
> the
> steering) after hitting a pothole or other such suspension upset.  It
> was easy to supress, by briefly stabbing the brakes or even a quick
> flick of the steering.  I chalked it up to the rubber stuff and
> shocks
> that had long ago worn out.
>
> Then, my transmission died.  Long story short, it refused to allow
> selection of 1st or 2nd.  No matter, I already had a line on a 6-speed
> from a Euro S6.  I dropped that in and was a happy camper, until I
> noticed that the tank slappers had become more common.  I could
> induce
> them on a smooth road by simply running the car up to 80 mph.  Also,
> it
> wasn't so easy to quell them.  The only solution was to drop the
> speed
> back down below 80.  I just thought that the suspension degradation
> was
> getting progessively worse.
>
> So, I ordered up all the parts: Bilsteins, H&Rs, control arms, inner
> and outer swaybar bushings, outer tie rod ends, upper shock mounts and
> bearings, motor mounts, front wheel bearings and maybe some other
> stuff
> I've forgotten.  I also replaced the inboard rear diff mounts because
> one was torn.
>
> After all that, the car is nice and tight as you'd expect.  No more
> tank slappers!  However, I still feel vibrations when I hit 80 mph.  I
> also
> feel them now at 40 mph.  I suspect they were there before, but the
> mushy ride was absorbing them.
>
> I've gone over everything to track down the source.  I ruled out the
> wheels by driving around with the urq R8s--that was an intersting
> look--and the problem was still there.  The propsahft carrier looks
> good, but I was going to take it to a driveshaft shop to have it
> balanced and checked out.  While I had the propshaft off, and the car
> on the lift, I decided to spin up the driveline for the heck of it.
> It still vibrated at an indicated 40 and 80 mph!
>
> So, I've isolated the problem to the front of the car, right?  I
> pulled off the halfshafts and ran the tranny up again.  It felt
> smooth.  OK, halfshaft problem, but all the joints feel OK.  The fears

> of a bum tranny crept into my head.  To test this, I put the propshaft

> back on and spun it up without the front halfshafts.  Big fat vibes
> again.
>
> I pulled the propshaft and put the halfshafts back on.  This time I
> ran it with just the hubs, no wheels or brakes.  I think I felt some
> faint
> vibes, but it's tough to tell.  Put just the rotors on, and the vibes
> were still faint, but a bit stronger.  Then I put on the wheels (a
> third
> set, just to be sure) and the vibes were there in force.
>
> So, all signs point to the gearbox.  With nothing connected, I guess
> the motor and tranny mounts isolate it pretty good.  It seems to need
> either
> the propshaft or the halfshafts to transmit the vibes into the body.
> I
> thought maybe it was the flywheel or new clutch, but it's always at
> 40
> and 80, no matter if the box is in 4th, 5th, or 6th.  That rules out
> everything from the input shaft forward.
>
> I have an S2 6-speed I'm going to throw in, but before I go to the
> trouble I thought I'd bounce the situation off you guys.  Has anyone
> ever heard of a tranny having this kind of harmonic vibration?  Is
> there anything I've overlooked?
>
> TIA,
>
> Eric R.
> '86 urq
> '93 S4
>
>
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