This is my friends car. We changed the u-joints last night thinking this would remedy the problem. it didnt.

When you hit about 75-80 MPH the car starts making a very high pulse vibration that you can hear also and feel in the seat.

Could this be the "vibe-shaft"?

His rear wheels also have a bit of up and down movment when the rear tires are off the ground.

Thanks for any help. josh.

 

i had a vibration after u-joints and i heard that flipping the DS 180 degrees can fix the problem - I got lucky and it did, takes 2 minutes to do so try it.

 

I have the exact problem with mine, and its a puzzler! My rear pinion yoke wasent holding the u joint tightly so I am putting a new one of those on tomorrow, but am not sure if that will cure it.

 

Ive been going through this too I tracked mine down to the tail shaft bearing. You can grab the driveshaft at my trans and move it up and down a good ways. It behaves like U-joints but Ive changed those too. Check it if all else fails.

 

Well I just finished replacing the pinion yoke as it was not holding the u joint tightly (had it staked as a temp fix) and now the vibe is almost gone! Now it only does it when you coast, ie clutch in or neutral.

I do have some up and down at the rear of the trans. From what I can tell by the exploded view of the trans I got from gm, the rear mainshaft bearing is the one? No slip yoke bushing on these, correct?

 

A bad U joint can wear these out form what I was told if it goes long enough. I always knew them as tailshaft bearing but the listing I found was output shaft bearing, correction bushing.

 

re balance the DS. Re balance the tires. Does it have a stock gear? A aftermarket gear will make these vibs worse.

 

If the ds was out of balance it would vibe all the time though wouldnt it? Its smooth as ever now if you keep a load on, no matter what speed. Before it would vibe over 80 mph, constantly.

It has aftermarket 3:73 gears, and I just rebearinged the diff because whoever rebuilt it the last time didnt clean the filings out and they wiped the pinion bearings.

 

I spent aobut $1300 dollars changing things before I found it was the tail shaft. I did everything your doing and had thd D.S. balance, tires, rear end done, and clutch and throwout bearing.

 

How was it to change? Can you do it in the car by removing the rear extension housing or does the whole trans have to come apart?