I have a bad viberation in the truck from 30 to 45 mph. Just started vibrating a few of weeks ago. I replaced the u-joints today 122,000 miles and grabbed the tailshaft to see if it moves. It moves alot is this normal? Also been hearing a whinnig noise for the last 20,000 miles or so at these speeds. I think it might be the plantary fixing to go. Viberation is still there after the u-joints. Can the plantay cause this much vibration?
My son is taking it to work tomorrow to balance the tires and check the front end. What do you guys think.

 

Sounds like tailshaft bushings are shot at minimum.

 

Thats what I was afraid of because the output shaft has a lot of movement and I see oil leaking on to the mount. Can this bushing be replaced by pulling the tailshaft off or do you have to gut the tranny?

 

You can replace the bushing by just removing the tailshaft housing.

 

Think I found the problem. REAR END. I put the truck on jackstands this morning and it vibrates bad 30 to 40. With the tranny in park I can turn the right wheel foward and hear bearing noises and it locks up. Turn wheel backwards and it frees up then locks up. I can do the left side and same results. I had a used G80 put in a couple of years ago and did not use factory bearings or not setup right. That's my luck.

Correct if I'm wrong but I should be able to turn the wheels with no problems and not lock up with the G80 right. It turn like an open rear end until it slips then locks in.

 

Update. Took the truck back to the guy who did the rear end and he said the rear is fine the driveshaft is bent/twisted behind the center bearing hanger. Had the shaft rebuilt and no more viberation.

Still can't see how it happened with the weak 4.8.