Hi, Guys

This is my first post, although I have been a regular visitor and user of the search function for the year and a half I've had my '99 XJ and for 6 months of research prior to buying. I can't begin to explain how much help I have received from CF in helping me repair/modify/upgrade my ride, and I am truly grateful to you all in sharing your experiences.

I am posting now because I am out of ideas in trying to eliminate a driveline vibration I have at speeds over 55 mph. I hear and feel a low frequency "Whoom, whoom, whoom" vibration that cycles every 2-3 seconds. It is not extreme, but annoying and tiring on 4-7 hour drives to Colorado to hunt and fish. It also makes it very hard to hear my 3 year old son in the back seat, especially since I already have some hearing loss.

Modifications I've done to the Jeep:

3" lift
Front: V8 ZJ coils with 2" spacers
Rear: New leafs with old main leaf added to pack, with homemade shackle
relocation bracket and new shackles

Iron Rock Offroad SYE
Rebuilt my old front shaft with new ujoints and centering flange and put it on back. I bought a used front shaft and pulled and regreased the ujoints on it to put on front.
6* shims under leaf pack to align pinion angle

New engine and transmission mounts
Old engine mounts were completely broken. This fixed about half of my vibes.

Tires
Have less than 10K miles on them and were recently balanced

Front/rear end
New front axle ujoints and hubs/bearings
New ball joints
Rock Krawler adjustable track bar
New tie rod and ends
New fluid in front and rear differentials

I've driven with just the rear driveshaft in place and have tried both driveshafts in rear but I still have the vibrations. Like I said above, I'm about out of ideas. My transmission (AW4 with NP242 Tcase) has recently started spitting fluid out of the front of the bell housing. It has been hot here (90-100) and I've already ordered an auxiliary cooler for it. Could there be a bad bearing or something else in the tranny causing the vibes? Its got nearly 200K miles on it. I've found used trannys on craigslist with ~125K miles for $350, so I may just swap it out anyway.

Thanks for your help, and I look forward to any ideas you all may have.

 

have you tried 4 deg shims in the rear axle ??

6 deg may get the numbers right when parked, but driving, the pinon will rotate up under torque, effectively increasing the angle.

I had to put 4 deg shims in mine.

Does moving the tire location around change the noise ???

 

Thanks for the tire suggestion, I'll rotate them tomorrow and see if that helps. I originally had 4* shims that I used to tilt my pinion down before my SYE. I turned them around to point the pinion up after the SYE, but the vibes are about the same with the 4* as with the 6*.

 

When you move the tires, do front to back first, then if no change do side to side to try and isolate which tire if any of it makes a change.

Next would be try an 8 deg shim.

 

Also possible bearing noise.

 

Any luck in fixing this? I have a similar set up with SYE and cannot figure this out. I am running out of ideas.

 

Similar problem with my 99. I'm at 19 inches from the center of the axle to the stock flare in back and 19.5 in the front. It's my understanding that this is a two inch lift though it works out to be about three from where I started with 18 year old springs.

Before the lift there was a wee bit of low frequency howl described by the OP at about 72 mph. After the lift the vibration and howl was worse and started about 30 mph.

Tried 4 degree shims = no change.

Took off the front drive shaft = no change.

Put the front drive shaft back in = no change.

Went to the local drive line specialty place to talk about getting my driveshafts balanced. Turns out the owner has 30 yrs experience and is a fellow XJ enthusiast. He crawled under my XJ and gave me a half hour of schooling. First thing he noticed was the four degree shims put the piņon angle too high and almost straight with the drive shaft, which is bad.

At his suggestion I changed both rear u-joints = improved quite a bit but not completely fixed

Also at his suggestion I went back to 2 degree shims = improved when accelerating

dropped the t-case 1/2 inch = improved to the point I don't notice the howl and vibration except when accelerating hard from a stop. No vibration over 45 mph now.

After talking with the driveline guy, I'm pretty sure the play in the t-case tail shaft is ultimately the problem and a sye is the fix. Trouble is I have a 242 TC which means it will be a while before I've saved up enough to fire up the parts cannon again.

FYI even a small ding on a drive shaft is enough to throw it out of balance. He also told me to mark the part that mates with the tail shaft and the drive shaft so they get put back together the same way they come apart, doing otherwise can throw the drive shaft out of balance.