Hi everyone,

I’m chasing a bad vibration above 50mph in my 2001 XJ and am looking for some help in diagnosing it.

The vibration:
-starts at roughly 45mph and gets worse as I go faster
-sounds like its coming from the rear end
-gets much worse/louder when I accelerate (sounds engine/driveline related). Accelerating harder at high speeds leads to worse vibration.
-can be felt in transfer case shifter and floor
-not affected by braking
-if I’m going 75 and shift into neutral, letting it coast, it virtually goes away

What I’ve tried so far:
-removed front driveshaft
-replaced both rear u joints
-replaced transfer case mount
-balanced tires
-replaced front calipers and rotors
-replaced steering stabilizer

Other issues, possibly related?
-pulls slightly left; at 60mph, if I leave my hands off the wheel, it’ll be drifting into the left lane in 3-4 seconds
-steering wheel neutral position (tires straight) is 1-2” off center, skewed left as well

Does anyone have any ideas? It seems to slowly be
getting worse so I’d really like to figure it out before I break something.

thanks!!

 

Because it goes away when coasting, it most likely on the driveline on a torque-bearing component (not tires, brake drums, or other things that would keep vibrating when spinning even when no torque is applied).

Items in play would be more like u-joints, differential, transfer case, transmission, torque convertor.

The most common culprit is rear drive shaft u-joints. Another is a rear drive shaft slip yoke that has developed too much play (not as common). But since you have already taken out the front drive shaft and did rear u-joints (good thinking!), the next culprit is exhaust pipe going over the cross member. It gets closer to the cross member when the motor is under load (torque) and can rumble it. Though this typically happens as easily in the driveway as it does at 70 mph. Because it is not related to rotation. But you already replace the transmission mount (also good!).

Another weird one is when bad rear tires/wheels resonate with each other at different speeds. If they are really bad they will vibrate at most speeds. But when they have slight problems, they sometimes become resonate with eac other (and the chassis) at certain speeds (frequencies). However, these will typically cause their problems regardless of acceleration or torque load on the drive line.

Did it always have this problem? Or did it develop out of nowhere?

Any possibility that rear axle has taken a hard hit lately? Due to your steering problem, I would also want to check the rear drums, but they are not typically sensitive to acceleration.

What condition are your rear leaf springs in? Weak old springs can contribute to axle wrap causing the rear differential to point more upwards causing strain on the rear shaft u-joints which will cause pretty immedate rumble/vibration. But this would be pretty noticeable even when accelerating from a stop (probably even more so).

Is there a lift?

Sorry for the random, had to deal with similar, just putting out the various things that helped.

 

Some background on the Jeep to answer a couple of your questions above: bought it last month with 95,000 miles on it. Bone stock, no lift or any other aftermarket components. I’m not sure how long it has had this problem, only that it’s been doing it as long as I’ve had it.

Re: the hard hit to the rear axle, I have no way of knowing - is there a way to visually check for axle issues?

The rear leafs appear to be in okay condition. One of them has a broken clip (not shackle but one of the retaining clips that holds the leafs together) but otherwise all seems to be in working order.

I forgot to mention earlier that the engine mounts look good (no visible cracks or missing rubber).

To further describe the noise I’m hearing: it’s an oscillating vibration, like something shimmying back and forth. The whole jeep shakes. I can feel it in my seat, slightly in the wheel, in the floor, etc.
I notice that if I’m going over 50mph and feather the gas on and off, I can hear something rubbing/settling into place. I also notice that when I accelerate at those speeds, my transfer case shifter moves maybe 1/2” (could be normal; I installed the Boostwerks aftermarket solid linkage) forward and then back when I let off the throttle.

The exhaust system is pretty rusty and crappy but I can’t imagine loose exhaust components could cause this amount of vibration right?

 

Have you tried putting it on jack stands and seeing if the rear wheels and tires are ok , and see if it has the vibration that way and you can see if the drive shaft turns straight or if it wobbles .

 

I would replace trans mount,

and check that all is good with trackbar

 

Engine mounts!

 

I'd do a real thorough examination of all the rubber - so engine mounts (these are easy to replace and inexpensive, btw), leaf spring bushings, and tires.

I'd start by switching the front tires to the back and seeing if that affects the vibe. If it seems to move the vibe to the front, then you know it's something with the tires - could be out of balance, could be warped tire. Even if the tires look good, if they've been sitting for some time or are old, they can warp. I chased a vibe that started around 55 for a couple months before realizing it was a bad tire. I had put on the full size spare that was original (12 years after buying the Jeep), but never used and assumed that since it had never been used, it was good. It was not.

Next it just makes sense to replace the engine mounts. Again, visibly they could look fine, but the rubber deteriorates over time and isn't absorbing the vibrations the way it used to. Considering they're inexpensive and relatively easy to replace. I'd just replace them.

Finally, the leaf spring bushings. Again, 3 bushings on each side (front frame, rear frame, shackle) and if the springs are older (as it sounds like yours may be) it may be that the spring bushings are deteriorated. Leaf spring replacement can be pretty time/labor intensive, so I'd eliminate all the easy stuff or be 100% certain it's necessary before doing the spring replacement.

 

Had a bad one on my zj for the longest time. Turned out the left front axle U joint was put in wrong. They have to be put in perfectly centered and if the person doing it cobbed it because the 4 little C clips would not all go on that will make them spin off center. Have to really take care and clean the grooves out and not compromise on that. All 4 clips need to go on.