I was driving on the highway the other day and this only occurs at 60 mph and higher. There is a slight oscillating vibration that seems to come from the rear end. At 60 and above the sound stays the same. Would axel bearings cause this or would they vibrate at any speed?

 

I would check u-joints first

 

Also the stock steel driveshafts are known to be out of balance and cause a vibration. So much so that GM issued a bulletin that allowed owners to get an aluminum replacement shaft under warranty. You can pick up an aluminum shaft from a 98+ car on here or ebay cheap.

 

Unusual for the stock DS to cause a problem at 60MPH. The problem usually shows up at much higher speeds, unless the car has 3.73 or 4.11 gears?????

 

Transmission mount???

 

The TSB that came out in 98 reported the issue at 90+ mph. Odd that it does not change pitch as speed increases.

 

I changed the rear, but I am not sure of the ratio (poss 3.23). The u joints are new. The car had some really bad tires on it when i first drove it, I cannot remember if the noise was present with the tires. I had new tires installed and now notice the issue. It really doesn't seem to be a bad tire or balance problem. I am going to look at the DS and the trans mount. I may just rotate the tires to see if the vib goes to the front.

 

One possibility.... pull the DS out of the pinion shaft yoke, and rotate it 180-degrees. Sometimes that will be enough to eliminate vibrations (or make them worse). But that would pin it down to the DS.

The drivehaft TSB was issued in 1996:

674101 MAR 96 Propeller Shaft - Vibration at Highway Speed

 

I think I have isolated the problem. Where the u joint meets the pinion yoke there are no locater "pins". There are just the girdles (straps) bolted but nothing to locate the u joint to a perfect center. There are grooves in the u joint where the clips could be clipped into place, but there does not seen to be sufficient clearance for the retaining clips with the straps bolted on. It looks like this 2fc8_12.jpg?t=1266272348

 

There should be raised edges on each side of the pinion yoke, that hold the caps centered between them. There were no clips on the stock U-joints.

 

OK thanks, I guess they are so slight that they are difficut to see. Especially when you're wedged under the car. haha