Hey guys, got an '87 Cherokee with 160,000 on it, original drivetrain going strong, hopefully. Going down the road the other day and all of a sudden felt a vibration in the driveline and had noise towards the rear while acclerating. When I decelerate I get a whining type noise from the back of the truck. Worst vibration is felt at about 45mph, and when slowing down from highway speeds, I get the whining at about 45mph also.

Truck drives fine, except for the vibration, and it doesn't sound like the diff to me, plus it came on all of a sudden, no warning like a diff would have. I'm thinking I busted at least one of the U-joints on the rear shaft, but haven't had time to pull it apart yet, or even look for that matter. Just figured I'd throw a post out and see if it sounded like a U-joint to anyone else, hopefully, because if it's the rear, it might be the end of this truck for me.

Thanks in advance, Mike.

Yep! Check the u-joint first.
Big JIm

Thanks Big Jim. Is there any quick way for me to look under at the shaft and tell whether or not the u-joints are busted or OK, or do I need to pull the shaft and then take the joints out?

Thanks,

Mike

Jack up the front end, put the front axle on jack stands, and watch the u joints as you rotate one side of the axle shaft while holding the other side still. If you see any play at the u-joints, replace them.

Sean

Thanks Big Bird, it's actually on the rear shaft, but I guess I can just do the same thing. What kind of play am I looking for, just any slop in the actual joint? i guess it will be semi-obvious when I do it huh? Gotta drive it about another 45 miles or so, to get it to where I can work on it, is that safe??

It should hold....

You should be able to do pull ups on the shaft without any noticeable play in the u-joint. Also you should be able to put a huge pipe wrench on the shaft and yank away without any joint problems.

Woops, my bad yeah same applies to the rear, and to what Sunder said, you are transferring all of the torque and HP your engine can put out through those u-joints so they should be tight. I had a bad vibration in my 79 Ford when I bought it which turned out to be the slip joint in the rear drive shaft. The dummie before me lifted the truck ~4 inches with out replacing the driveshaft with a longer one. It would only vibrate when the drivetrain was unloaded though. I drove it for about 7 years before the slip joint finally stripped out, I knew where in the drivetrain the failure would happen though, so I knew it was somewhat safe to drive that way. If I had bad front u-joint I would be a little hesitant to drive it hard or very much, because if that u-joint fails your drive shaft will act like a pole vault for the rear end of your rig.

Sean

cpec usually you can lie under the vehicle and push-pull-shake in all directions with all your might on the shaft near the joint and get a bad one to flex a bit in the joint! Do this in neutral so the shaft has no drag on it. ANY movement means it is bad. I have seen em with the bearing completely gone from time to time.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks for the info guys. I will look at it ASAP. The 45 miles I have to drive are all highway, so hopefully the joint will hold out if I keep it slow around 55 or 60. I definitely don't want to be pole vaulting down the road.

Any info on how hard it is to pull the shaft out to replace the joints, never done it on an old Jeep.

Thanks again,

Mike

It is the same on everything... A firsttimer should be able to do it with limited tools.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />