Drive shaft Vibrations
 

I have a 1988 Full size blazer that I just installed a 4inch lift and when I took it for a test drive down the road I noticed that when I let off the gas, I could feel and hear what seemed to be my rear drive shaft vibrating. As soon as I got on the gas it would stop and start again when I let off the gas again. Any ideas what would cause this. Anything helps.

Could be the u-joints or could possibly be a worn slip yoke at the back of the transfer case.

Did you have the drive shaft off?

Yes I had my drive shaft off and I had my buddy looked at my U joint and said it was good, but now I'm just going to replace it anyways. I it look old to me.

High mileage u-joints will vibrate when their "worn in run patterns" are changed with things like greater angle due to a lift. Should be an easy fix with new u-joints.

I always mark the driveshaft and the yolk (with chalk or paint) to make sure that it goes back in the same position as it was removed. Changing the "phase" can cause a vibration. You may have to rotate the driveshaft at the rear u-joint.