Another vibration at speed thread.

98XJ, Auto, 4WD, 4.0, stock wheels/tires, no lift.



Vibration 55-65 MPH. Feels like coming from under the seat.


Rear drive shaft removed: no vibration (but TC a bit louder than I'd like).


Drive shaft balancing (reportedly was very good) and new U-joints did not change vibration (nor did loaner driveshaft).


TC output shaft seems solid, no wiggle at case. Splines seem good and when twisting drive shaft no play in slip yoke. But there seems to be a little up-down wiggle in the slip yoke. When grasping drive shaft behind first u-joint I can move it up and down slightly, the movement coming from the slip yoke.



Rear inion seems solid with no side to side play. But there seems to be, maybe, excessive backlash. Measuring at rear u-joint 8mm bolts, I can twist the driveshaft so it moves 1/16 to 3/32"


Any ideas?

I'd be very suspect of the slop in the slip-yoke!

I learned.
Replace any u joints with old boots.
They are cheap.
Easy to change.
And failure is not worth the risk.

Could be the bushing in the tail of your t case. Even though it goes away without the shaft try getting your tires balanced too

Sounds very much like a tire balance problem. Tires will normally show a dynamic imbalance at 3 speeds, 35,55 and 75 mph give or take a few on each side. You may only see it one of the three speed ranges. I would start with the rear wheels since you feel those in the seat. Front wheel imbalance will be felt in the steering wheel.

Rotate tires and see if vibes go from seat to steering wheel.

You say you replaced all the ujoints, but did you replace the centering ball on the dual cardan?

How much shaft engagement do you have at the slip joint? Too little will lead to bad vibes.

How did you run without a rear shaft without dumping a ton of xfer case fluid?

Thanks all for the ideas. Some replies:



Vibration is not major. May 21 y/o daughter riding with me, or driving, does not notice it.



Soapy and SMC, I did rotate the tires. It did seem to change it from front to back. Then got back tires balanced. Much better but still there. Most of the time this is a tire balance issue but I figured not since it went away when I took out the rear driveshaft.


RCP: I'm not sure if the slight amount of play I feel in the slip yoke is normal or not. I thought perhaps putting it on stands, as described below, might help diagnose that.




Old man: Vibration is present with front drive shaft removed, so I don't thing it is the cardan or u-joint on front. NP231 case has output shaft at rear and sliding off slip yoke won't release fluid. Slip yoke doesn't have much room to go on further.


One new thing: put the rear on jack stands yesterday and spun tires to 55-60 mph (where I feel the vibration). I didn't feel any vibration with it on stands. Had my daughter push the pedal while I watched the driveshaft. It seemed to rotate smoothly. Didn't see any bouncing at slip yoke or elsewhere.


But the exhaust did bounce quite a bit. There is no hanger between the transmission mount hanger (pipe is well clear of trans mount) and rear axle area at times it would be going up and between those hangers.


I have set of stock aluminum rims, much lighter than the stock steel ones. Maybe I'll go ahead and get tires mounted on them and try that.

There is supposed to be one hangar back aft of the muffler where the tailpipe turns for the bend that takes it up and over the rear axle, and one more next to the gas tank. The only other "hangar" is part of the transmission mount.

With the tires off the ground, I wonder if you're changing the loading on whatever is vibrating. Being on stands, the weight on the suspension is the same as on the road, but most of the weight that would normally be on the wheel bearings is removed. Still, seems like we should be able to learn something from that test.

Anyway, the crossmember is approximately under the front seats. Have you looked at the condition of the engine/trans mounts, and double-checked that the crossmember-to-frame bolts are tight?

I just did my ball joints axle u joints and hubs today because of a developing wobble.
it made a noticeable difference.
check ball joint play ?

Soapy1 said:

Sounds very much like a tire balance problem. Tires will normally show a dynamic imbalance at 3 speeds, 35,55 and 75 mph give or take a few on each side. You may only see it one of the three speed ranges. I would start with the rear wheels since you feel those in the seat. Front wheel imbalance will be felt in the steering wheel.

Click to expand...

To update this thread, having tires balanced did not help. But new tires did the trick. No vibes at the 55-65 mark anymore. Also after year I've turned the XJ into a reliable (knock on wood) machine that has made two 700 mile round trips to Florida. About $1500 in parts into it.