YJ: Transfer case troubles?

[aido62]

Hey all,

This is my first post, and I hope I don't wear anyone out with this! I have an issue that has been plaguing me for the past two years, and I'm hoping that someone here might just be able to help me figure it out.

I have a 90 4.2L YJ, which I have done extensive, exhaustive work to, including, but not limited to: a new motor, nutter bypass, team rush and HEI module ignition upgrades, rebuilt (twice) manual transmission, checked front diff once and rear diff twice, new ball joints, u joints (front end axles and rear drive shaft), front wheel bearing hubs, new tires (balanced twice, and NO uneven wear), and had the drive shaft spun, and the U joints double checked, by a top notch shop in Nashville. Everything that anyone has EVER recommended has been done!

Now, the problem....

I have a shuddering vibration that can be felt in the steering wheel and the stick in 3rd or 4th gear. It's felt everywhere else, but not as severely. It comes on at 32 MPH and quits at roughly 50MPH, ONLY with my foot on the gas. It seems to go away if I feather the gas a bit. When it happens, it feels like the Jeep is really struggling. The strange thing is that it ONLY happens after I've been driving for a while (after an hour or more usually-WEIRD!). It GOES AWAY if I put it in 4WD HI. It also GOES AWAY going down hill, and it GOES AWAY in neutral. Some days (yesterday) it feels like a brand new Jeep with NO vibration. When it's NOT there, this Jeep is AMAZING! I'm perplexed! I did remove the rear DS and drove it in 4WD Hi. Rolls smoothly. The transfer case main shaft seems to rotate in a very slight elliptical pattern, but it's SO slight that you have to really look to see it. I plan to replace the tail cone bushing and seal, because I slipped the cone over the slip yoke and found I could wiggle it around a bit, so I'm wondering could this be my issue?? There seems to be NO play in the main shaft at the bearing, the shaft looks straight, and the bearing looks like it's working perfectly. I ran it in 1st and 2nd gear on jack stands with the tail cone off so I could see it working. I just simply can't think of ANYTHING else. Should I dig deeper into the TC or ????

Sorry this is so "wordy", but I don't want to waste anyone's time leaving out details. Have I missed anything? ANY help would be SO greatly appreciated!

Thanks!
A

[Zoobi]

Whats your rear drive shaft angle? Do you have polyurethane mounts?

By your description, it kinda narrows down to drive shaft/rear end. If your drive shaft angle is too steep, you will get a vibration. On my CJ7, it would come in about 45 and go away about 60. I got a cv drive shaft and the problem was solved. Now if the vibration keeps happening you will wear the tail shaft bushing and seal.

A rear diff issue will change more with load (accelerate/decelerate). Pulling the drive shaft takes the load off the rear also. The part where you say it changes on decell and neutral, points at rear end. But you wont feel it.

Also crawl under and look for things rubbing frame or body. Something we call "ground out" is also possible. Last weekend I got a call from a friend, noise vibration in his 84 Toyota Pu with an 04 gm v6. I drove around with him and looking underneath I showed him where his exhaust was just touching a cross member. His problem happened at 65-70 mph. At that speed the engine torqued just far enough to make it hit. Between that and his poly mounts, it was very noticeable.
So how about this.
1.Your drive shaft angle is wrong, the vibration has worn the back of the transfer case allowing it to vibrate more.
2. You have a slight issue with the rear diff and it surfaces while your diagnosing your vibration.
3.You have something touching between engine and body(or frame) that shows up when the engine torques just right. This one can come and go. These can be exhaust pipes, a bolt sticking down from a seat belt, a bracket bent too close. You get the idea.
Want to make any of these more noticeable, if you have a polyurethane transfer case/ transmission mount, this will transmit vibrations a rubber mount wont.
Don't rule out a weird problem in the transfer-case but I doubt that would be it based on your description

Ive spent most of my life working for GM. One of my specialties was vibration/noise. I can tell you this, some people can guess pretty good but when they've run out of guesses, here you are. Without hearing/ feeling the vibration kinda makes it rough. You gave a pretty good description.
Good luck, I hope this helps you.

Scott

[Zoobi]

Thought about it and your description seems to favor a "ground out". Do a very good check of everything. Don't forget shift levers, motor mounts, trans mount and what ever you modded from exhaust system to cross-member skid plates. Look for shiny spots where they've been rubbing. Ive seen rocks stuck between trans and body, stereo amp installs where the screws touch the transmission. Remember, the body/frame and drive-line/engine cant touch or you get noise.

Scott

[vwtipeii]

I don't know anything about anything.. but would a SYE kit possibly help here?

[Zoobi]

That and a cv drive-shaft, even if it's not the issue, you bet it would

[6spdYJ]

Are you running a solid shaft in the long tube? Is your front diff locked or welded, or does it spin freely? Have you pulled the front D/S? Feeling it in the steering wheel and the stick indicates something that connects the two. A bent shaft will shake them both. If it stays in the stick, like Zoobi said; what's the rear D/S angle? If it stays in the wheel, start looking up front. The bushing in the cone is very important.

[aido62]

Hey guys,
Thanks a lot for the responses. Here's an update. Installed a 2 1/2 lift last weekend. Paperwork said 6-8 hours. Didn't say [I]anything[I] about "per day". With the lift installed it all went pear-shaped. Driveshaft U joints clacking away, and unbelievable vibration! Lowered the TC an inch (no SYE or CV DS yet) and it got better. Lowered it another 1/2" (I know-not a great idea) but it helped more. I am replacing the tail cone bushing and seal, along with the main shaft bearing in the TC this weekend. I hope this will make things a bit better, because there is a tiny bit of wobble in the main shaft. I will definitely install the SYE etc in future, but I have to wait for the funds to be available. I can't see anything grounding out, and since the symptoms get better after lowering the TC, I'm guessing that I'm on the right track? Any other suggestions, or anyone else's opinions are welcome.
Thanks again,
Aidan

[aido62]

I'm sorry, I meant to answer your questions too. My rear DS is stock, but in really good shape. Had it checked at Clinard's in Nashville, a top notch shop. Said it was the best Jeep DS they've looked at. I've had the rear diff open twice and it looks great inside. No obvios signs of wear, although it does roar a bit rolling down the road. There is a very small bit of play in the pinion gear when you reverse direction on the DS by hand. I'm assuming this is called "backlash" and is considered acceptable? The rear Ujoint has roughly a 1mm side to side space between the end caps and the yoke ribs that hold it in place. The yoke has straps, not Ubolts, but they seem to remain tight. I have not pulled the front DS only because it runs smooth in 4WD hi with both DS's AND with only the front DS in place. Should I anyway? As for the front diff, I'm going to have to say it's stock, whatever that means, unless there are specific things I can look for. I'll add an update after I've done the tail cone bushing etc.

[vwtipeii]

I still don't know anything about anything but I just had my motor mounts swapped to Currie +1". This is supposed to help the driveline angle as well.

[6spdYJ]

Check out Tom Wood's site 4xshaft.com. Look at the tech info and geometry 101. It will answer any questions you have about driveshaft angles.