I have a 1995 Chevy 1/2 ton with a 4" lift. I had the rear end rebuilt about 4 months ago. A real bad vibration occurs in the rear of the truck between 45 and 55. Also when I let off the gas abrutly going about 65 the driveshaft almost wants to bind up and the bolts on the u-joint are hitting the driveshaft. It is almost like the axle is moving and the angle of the drive line is changing. When the truck is just sitting the angle is fine also I replaced the u-bolts and u-joints but that did not take care of it. The truck has been lifted for 6 years and did not do this before the rear end was done. Is it possible they put something together wrong in the rear end when they did that or is it more likely that there is a problem with something like bad leafs or something. Thanks for any help.

 

Check your leafs for cracks, also do you have a wedge or some kind of pinion angle aligner onyour lift? While you are there just double check the U bolts on the rearend.

 

I checked for cracks and did not see any and also have tripple checked the u-bolts and also the blocks are tappered and the alignment looks good when it is just sitting.

 

Try having someone sit in the truck and have them shift it from drive to reverse and back while you look at what the rear end is doing. That should give you a good idea of how much it is moving when torque is applied in both directions.

 

Could be a bearing issue or spacer in the rearend. I would try removing the driveshaft and seeing if there is any strange movement in the rearend, and then the same on the transfer case. Then maybe have someone stand in the back of the truck and jump in the bed while you check the suspension for strange movement.