Vibration getting worse

[bearcrawl]

I am getting a pretty bad vibration while coasting. Accelerating, fine. All the way off the throttle is fine. Coasting while just touching the throttle I am getting a pretty loud and fairly violent vibration. Could be the U-joints I guess. Seems to be coming from the rear of the truck (88' lla). How do I check the U-joints. Just installed Parabolics and that made the vibration worse.

[SafeAirOne]

How do I check the U-joints.

I'd chock the wheels, put the transmission in neutral and get under there and yank the driveshaft this way and that way near each universal joint and look for excessive movement.

[I Leak Oil]

The U-joints shouldn't have any play in them. As suggested, give them a push/pull test. Also, make sure the bolts holding the shaft to the transfer case and diff pinion flange are tight. Check the driveshaft slip joint for excessive movement also. Slim chance it could be the axle drive flanges are loose, pinion nut loose or transfer case output flange is loose.
Be safe a chock the wheels while doing this...
Jason T.

[adkrover]

I'm guessing the parabolics only accentuate the vibration because they are more flexible, they are allowing the rear end to transfer more vibration to the frame so you feel it more. It's unlikely that the spring job actually made it worse, you're just able to hear and feel it more now. Since it's not there under load (either positive or negative load) it must be in the drivetrain so if it's not the U joint, then check everything for play from the back of the transfer case all the way through the rear axle to the hubs. Could definitely be a more major problem with the ring and pinion. Drain the rear end and look for metal fleck in the oil.

[bearcrawl]

Went to town on the rear driveshaft. Everything seem nice and tight. all the bolt are there and tight. Could it be the ring and pinion?

[bearcrawl]

Very interesting new development. Pulled the fill plug from diff and had suction or vacuum. Could that be the culprit? Going to mess with the breather.

[scott]

have you drained it? use a paper coffee filter. i hope you find nothing metalic in there

[BackInA88]

I am getting a pretty bad vibration while coasting. Accelerating, fine. All the way off the throttle is fine. Coasting while just touching the throttle I am getting a pretty loud and fairly violent vibration. Could be the U-joints I guess. Seems to be coming from the rear of the truck (88' lla). How do I check the U-joints. Just installed Parabolics and that made the vibration worse.

Don't parabolics come with tapered shims to correct the pinion angle since they do lift the rig?
Have you tried pulling the rear drive shaft and just running on the front?
Did you check the flange nut in the center of the e-brake under where the drive shaft flange bolts up as Jason suggested?
Transmission mounts OK? Get a prybar and made sure they haven't separated.
If you take the drive shaft out use and angle finder level and check the mounting flanges at the trans and the diff, they should be the same or at least with in a few degrees.

Are the u-joints clocked correctly? The caps should be in-line front to rear.

Steve

[bearcrawl]

pulled rear prop shaft. Vibe still there. Really hoping trans mount is busted. Could this be a gearbox problem?
Checked flange nut in middle of brake under drive shaft. Tight and looked new.
Thanks for all the help guys

[SafeAirOne]

Don't forget the front shaft--It spins when you dirve too (unless you have front locking hubs and they're disengaged).

[bearcrawl]

Yep, got locking hubs.
thanks

[adkrover]

So if your saying you drove the truck on the front axle with no rear drive shaft and it still had the same noise, plus the vibration changed from loaded to non loaded as far as coasting vs. pulling, then it can't be in the rear axle. Without the rear driveshaft, the rear axle is in coast only mode and the throttle position should have no effect. You should do the same experiment with the rear shaft installed and the front shaft removed. Then you'll know it's not actually happening in the front axle. If it still happens when driving with rear axle only, it would have to be in the gearbox or engine.

[bearcrawl]

After a bit more research I have a feeling it might be my Fairey. Getting real bad now.

[SafeAirOne]

After a bit more research I have a feeling it might be my Fairey. Getting real bad now.

That doesn't sound cheap!

[I Leak Oil]

You may want to remove the OD and check the main shaft nut! If this is loose it can cause all sorts of noises.
Jason T.