My '86 has a drivetrain vibration that is getting worse.. Here's the kicker... I've got the angles for the diff. and transfer case identical. Got a driveshaft with new U-joints and balanced. The vibration occurs when there is NO load on the drivetrain. Coasting in neutral at speeds over 50 MPH or is not a fun experience. The weird thing is under load for both acceleration and deceleration, there is very little if any vibration. So, I'm thinking either my pinion bearing, or transfer case? what would be the highest suspect? thanks in advance for the help!

Vibration under low loads is a sign of something loose. Slip yoke (try separating and brushing splines w/ grease), pinion or t-case flange (tranny in neutral, e-brake on, grab flange end and pull, fell for up-down or side-side play - there should be none).

OK, there is some play in the T-case flange. Also, there is a lot of slop when turning the driveshaft CW and then CCW. Is this a sign of improper pinion/ring engagement?

OK, so I took the truck down to AZ driveshaft and they determined that my rear driveshaft was too short and causing the vibration under no load. I do have about 5" of lift on my '86. For all of those with lifted trucks, did you lengthen your rear driveshaft? I will be picking up the truck tomorrow and we'll see if this indeed resolved the problem... Stay tuned

That's about what I have on my '85 PLUS a 2" drivetrain lift. Mine's OK. I'm curious to hear what the shop is doing to fix yours. Let us know!

I Picked up the truck this morning and yes, there is less vibration now. They lengthened the driveshaft 2" and rebalanced it. There is still a little vibration but noticeably better. <img src="/forums/images/graemlins/kewl.gif" alt="" />

I can picture it in my head. Your slip joint portion of the shaft was basically pulled too far apart, causing excess wobblieness(sp?). Lengthening the shaft therefore increases more spline engagement for less slop. This may be where a driveshaft spacer would also help. Now you got me thinkin'.........

I had a less-than-scrupulous shop build me a driveshaft with some junk 'long-travel' slip joint that was machined off-centre. It would balance on the machine but it wasn't spinning on a single axis. Took me forever to finally figure it out. Replaced the junk with a Toy part and it was fine.