Differential or suspension?

[Dihrdbowti]

Hello all. First I would like to say that I am a new diesel owner and I have found this forum to be invaluable. Ok here goes I have a 96 GMC Yukon with the 6.5L TD. I seem to have not really a noise but more of a feel. Whenever I stop or start if feels as if the back end either drops suddenly (acceleration) or raises up (stopping). From a stop I can start out slowly and can keep the backend from dropping for a little bit but as I accelerate harder it will drop. I was in the tranny shop after a complete rebuild of 4L80 and T-case to make sure everything was ok after a few thousand miles and the tranny guy said it was in the diff. I just have a hard time believing that. I do not have any other noises or issues with the diffs but the suspension seems to sag a bit in the rear. Any and all comments views etc are welcomed.

Thank for any help

[DennisG01]

I may be stating the obvious, so forgive me in advance. What shape is your suspension (shocks) in? Maybe it's time for replacement. What happens when you push the rear bumper down (jump on and off it)?

[Dihrdbowti]

A new set of Bilsteins are on the list but the suspension doesn't bounce around. When I jump on then off it flexes down then back to it's original position. I'm a pretty big guy at 250lbs so the suspension does move. when I stay on the bumper and jump up and down it moves with me and whenI stop it stops within one bounce. I suppose I just need to crawl underneath and pull the leaf springs and check all the bushings. One other thing I believe that this might have had a snow plow. The front suspension has been redone with poly bushings in most places.

[catmandoo]

could the rear brakes be hanging up?have you checked the linings and the real axle seals,you get grease on em and the brakes will grab something fierce.

[diesel65]

It could be a classic case of torque bind in the rear driveshaft slip joint.
When you come to a stop using the brakes the rear end will lift and that causes the driveshaft yolk to pull out of the transfer case, after you come to a stop the torque of the engine will prevent the yolk sliding back smoothly into the transfer case.
To verify that this is happening put the transmission in neutral before you make your stop then put it back in drive when your ready to move again.
Gm has a special teflon grease to lube the splines but I remember it was like $24 dollars for a small can.
The other option is to replace the output shaft in the transfer case and the yolk on the driveshaft.

[Dihrdbowti]

So on my way to work this morning I put the tranny in neutral while coming to a stop and back in gear when before starting. Lo and behold i wasn't feeling it. It is a short trip to work so I will drive around at lunch to verify this but this is starting to make me feel better. I would rather spend $24 vs. $1500 any day of the week. Thanks Diesel65 I will get you an update this weekend.

Catmandoo I went through the brakes and seals and everything appears to be working correctly.

Thanks again