I just finished putting a new clutch in my 96 LT-4. While I had it apart I had the u joints replaced in the driveshaft (I don't have a vise or press,bummer) I now have a vibration above 70. I'm guessing a driveshaft problem but could I have screwed up the c beam alignment? The bolts went in with no forcing and are tight. I'm thinking of pulling the driveshaft and getting the balance checked, yikes.

 

did you mark the driveshafts when you removed them? I had this occur with one of my driveshafts on another car turned it 180 and that fixed my prob....

 

I've delt with lots of C4 driveline vibration issues in the past and may be able to shed some light on this problem.

I would first try repositioning the driveshaft 180 degrees from it's current location and road test the vehicle.
If rotating 180 degrees makes the vibration worse, return the driveshaft back to the original position and move downstream.
Check the half shaft u-joints by hand and have an assistant grab the rear tires at the 12 and 6 o'clock position pulling and pushing the botom of the wheel in and out. Watch the u-joints for movement indicating worn u-joints. Replace any u-joints that have movement and make note if any of the u-joints are leaking greese from the seals.

Now for the likely vibration culprit...
C4 Corvettes are prone to wheel vibration related harmonics especially at the 70-80 mph speed range.
Wheel vibration can be caused by the rim/tire assembly being out of balance or when excessive free run-out is present. Free runout is the amount that the wheel contact surface increases and decreases from the wheel axial centerline as it roles down the road. Both rims and tires usually have a little bit of free runout. In most cases, free runout can be minimized (brought to within 0.050" specified tolerance) by having the wheel assembly balanced on a Hunter GSP9700 wheel vibration control balancing machine. With a competant operator, this type of wheel balancing device can determine the individual wheel and tire free runout and direct the operator how to re-orient the tire on the rim so as to best cancel out free runout of the wheel/tire assembly. The newly oriented wheel/tire combination is then balanced within specifications.

You can locate a GSP9700 equipped shop nearest to you by going to http://www.gsp9700.com and click on "Find a GSP9700 near you".

Hope this helps.

See Ya,
Bill Boudreau (ZFDoc)

 

Did you use an alignment too to install the clutch? Also, did the drive shaft didn't get banged around at all while it was out? All it would take is the slighted deformatty from being banged around to cause vibration at the speed that thing spins. Did you mark the yokes and driveshaft so they could be installed in the exact position they were originally installed?

 

I did mark the shaft and tried t get it back in the correct spot. I think I'll try switching it 180 and road test. If I take it to a machine shop for balance check do they check the u-joints installed? I hate vibrations!