[jose_p_adams]

My jeep is eating up U-joints. This has apparently been going on since before I owned the jeep but this is the first time I've had an opportunity to assess the situation. I'll try to give as much detail as possible, hopefully I don't miss anything.

I have a 1997 TJ with 4.0L engine, stock manual transmission, stock NP231, Dana 30/35 with 3.07 gears and 35" KM2's. I have a suspension lift of unknown origin but I think it is a 4" lift. The front upper control arms are adjustable the front lowers are fixed length. The rear control arms appear to be stock. The transfer case has the stock slip-yoke output and has been dropped ~1.5 inches.

The issue that I'm having is the jeep is eating up the rearmost U-joint in the rear drive shaft. At the end of January I rebuilt my front drive shaft with new U-joint/centering ball. The centering ball was starting to make some noise and I decided that since I had it out, I should just put new U-Joints in since they had quite a few miles on them. Later that night, I noticed that the rear Ujoint in the rear drive shaft was toast. I had planned to go wheeling the next day so I inspected the Ujoints I had removed from the front and put one in. Then I reset my odometer. Since then I've driven 121 miles and the rear ujoint is once again toast.

The most recent failure has the same characteristics as the previous. The needle bearings in the 2 caps that are mounted to the pinion yoke have basically been crushed into a powder and the 2 caps mounted to the drive shaft are completely undamaged. The cross is also damaged under the caps on the drive side of the cross. I suspect that occurred after the needle bearings failed.

I had an opportunity to discuss the situation with the previous owner. He indicated that everything was fine for 5 years after he installed the lift then the stock ujoint failed. Unfortunately I have no idea what date this happened on. He installed a lifetime warranty ujoint from pepboys. He said it would fail about once every 6 months and he didn't think much of it because it was easy to install and pepboys was giving him the new ujoints for free. He said he though it was just because they were cheap ujoints. So he's either exagerating how long they lasted or the situation has become worse. I also noted in the maintenance records he gave me that he had the rear pinion yoke replaced in March 2008. No reason was given as to why the yoke was replaced but I suspect it was related to the same issue.

Other notes:
The front Ujoint in the rear drive shaft appears to still be the stock unit and is still in good shape.

When I replaced the Ujoint the first time, I had to lay on my back under the jeep and push with everything I had with both hands to get the drive shaft to go far enough into the slip yoke to get the rear ujoint back into the pinion yoke.

I have no detectable driveline vibrations even up to 70 mph. I can't say faster than that because I don't drive faster than that.

Here are some pictures:

This is the stuff that is inside the pinion yoke caps. Its a combination of grease and mashed up needle bearings:


This is the damaged cross. The other side looks about the same:




Here are the drive shaft side caps/cross:




I think that's about it. Any thoughts would be much appreciated.

[TDHofstetter]

That grease doesn't look 120 miles old - it looks a LOT OLDER than that! Did you grease that used joint when you put it in?

It sounds an awful lot like that driveshaft is too short - on compression it'll shorten further, and it may be beating the u-joints to death every time you drive over a bump.

[Jerry Bransford]

Post a well-lit photo from the side so we can see the rear pinion angle where it attaches to the rear driveshaft. I'm betting you have a rear pinion angle problem where the angle is not correct for the type of driveshaft you have.

You are certain you don't feel any drivetrain vibrations at all up through the seat of your pants as you drive around? Also, at the front of the rear driveshaft, please verify it has just one u-joint and not two.

[jdhallissey]

Wow even when my driveshaft was to long it didn't crush the bearings. I am with jerry on this, I believe your rear pinion angle is so far off that the u-joint has no option but to crush those needles, PICS PLS

[jose_p_adams]

I put new grease in the ujoint when I reused it. I didn't rebuild it but I did pack each cap with new grease when I put it back together. I estimate that the used Ujoint I put in the rear drive shaft had 123k on it but it was still in good shape. So I guess the average age of the grease you are seeing is 60k miles.

I also checked to see if there was anything that may be causing the slip yoke to bind. I didn't find anything. It slides on and off of the output shaft with no issues but doesn't seem to allow any slip which would shorten the driveshaft.

[Jerry Bransford]

Again, we need pics of the rear pinion angle where it meets the driveshaft to offer any help. We're working in the blind until you can post those pics.

[jdhallissey]

Jerry I thought you always working in the blind with the eye patch on

[Jerry Bransford]

Originally Posted by jdhallissey

Jerry I thought you always working in the blind with the eye patch on

In more ways than just that.

[jose_p_adams]

Originally Posted by Jerry Bransford

Again, we need pics of the rear pinion angle where it meets the driveshaft to offer any help. We're working in the blind until you can post those pics.

Started the previous reply prior to reading the picture request. I don't get any driveline vibes.

Here are the requested photos:

Here is my drive shaft. One Ujoint on the front. One on the rear. It measures around 13 inches from the top of one ear to the top of the other. Center ujoint to Center ujoint is about 12.


Driveshaft angle pics. I don't have a ujoint to hold it in there so you'll have to use your imagination for that part:









Here is where the drive shaft atttaches to the transfercase:

[jose_p_adams]

The Ujoint angles don't appear to be in bearing crushing territory to me.

[Knuckelhead]

The pinion angle is too high...IMO

[Jerry Bransford]

As I suspected, the rear pinion angle is way too high and is definitely the reason for your u-joint failures. For your conventional non-CV driveshaft, the rear pinion angle must (!) be parallel to the transfer case's output shaft as shown below.

[TDHofstetter]

Jack up the frame so both rear wheels are off the ground. You'll find that the axle moves forward when you do. See if the driveshaft fits in there then - with both wheels off the ground.

[bean66]

Looks like the pinion angle is too steep.

They output angle from the transfer case should be at the same angle as the pinion output.
They should be parallel.

Unfortunately since this is lifted it will be very difficult to accomplish.

Get a Double cardan drive shaft and a SYE and adjustable upper control arms. Then you can set up the output so it points directly at the transfercase output.

[jdhallissey]

Try this take your t-case drop out- That will give you back your more parallel tcase/diff angle.