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I have a drive train vibration that has shown up. Any ideas?

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Over the last week or so, the Jeep has developed a vibration that is not in the engine. It's not a course, vibration but one that will make things vibrate in the utility box above the glove box or even make my collection of keys vibrate hanging off the ignition. It seems to be at most speeds but perhaps lessen at some. I can take it out of gear and rev the engine and and it feels fine. It definitely lessens if I take it out of gear and just coast and gets worse as I pull up a rise in the road. It doesn't seem to change as I change gears. Changing gears is fine. No issues. The more load the drive train has the more it does it.

I've been under the Jeep a few times looking for something like a loose U joint or loose bolts holding the transmission in. Nothing is visible and I have tried twisting the drive shaft by hand to feel for something. I haven't yet jacked the back wheels off the ground and rotated the drive shaft, but I plan to. The only thing I have found is the trans rear seal needs to be replaced. It looks OK, but I have a stripe of wet on the bottom of the Jeep where the shaft has spun fluid. I checked the level in the gearbox and it still dribbles out when I remove the bolt on the side. It is also leaking a bit from the front of the trans. I hope it is the oil pan and not the rear main seal. I had that replaced last year when I had a new clutch, flywheel, and slave cylinder installed.

I don't think a rear wheel bearing or issue in the diff would be likely, as it has had an easy life as far as any off paved road going is concerned. ( No rock crawling or crazy stuff )

If you've read about or had an issue like this and a suggestion of what to look at, please reply. I'm considering new U-joints just to rull them out, even though I don't see or feel any issues when I move the drive shaft by hand.

John
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Discussion Starter · #4 ·
I don't think it has a SYE/CV. ( I haven't googled that acronymn yet. ) The drive shaft it really very short. It's a stock Jeep with no lift kit or any of that.

I'll go wrestle with the drive shaft....

The rear one, attached to the diff is rock solid. The front one, may have a little play. It's hard to really tell, since the output shaft of the trans moves a bit, even in gear, but I would say it has some. What's the recommended U-Joint in the forum. I may as well change it and the rear trans seal, while I'm at it.
 

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Discussion Starter · #6 ·
The front shaft doesn't turn in 2WD, and I rarely drop into 4WD. So, unless the front axle is quietly trying to engage , I'm not sure what dropping the front drive shaft would do. But, I am willing to learn!
 

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Discussion Starter · #10 ·
Rockworm,

The Jeep may be 30 years old, but just now clicked over 90K miles.

Jeeper,

There may be something to the front shaft. I tried to listen to noises while driving today. I heard an occasional clunk from the front. Is is possible for the front axle to be close to locking if the vacuum valve has issues? I made sure it would go into all the 2 and 4 wheel drive settings before going anywhere and it felt right. I need to check in the daylight.
 

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Discussion Starter · #13 ·
I checked out the front driveshaft today. It is obvious at the transfer case and tight at the front axle. I would say a few mm worn. I can hear it and feel it when I hold the yoke and move the shaft by hand. The rear was was only a " I think it moves " in comparison. Getting to the rears looks easy. Getting to the front at the transfer case will be harder due the cover plate that also holds the transmission in place. There is a window in the plate, but it won't be a cake-walk.

I'll just get all 4. Anyone recommend a brand of U-Joint? I could just go by online reviews. Gease-able or sealed ? The stock ones are grease-able, but I didn't know that until now. They never got any new grease since 1992.
 

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Discussion Starter · #15 ·
I just read your post on U-joint installs. Thanks. That will be really helpful..

As I've driven the Jeep around, listening all the time for another symptom of where the worn part might be, I have noticed a sound, most often when I start from a green light, a small clunk sound. The first time I heard it I figured the trans guy that replaced my clutch and stuff didn't get one of the trans mounting bolts tight. I couldn't see evidence of that from under the Jeep. Just adding this to the list of symptoms for you all to consider.
 

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Discussion Starter · #17 ·
I finally got the time to swap the U-joins on the rear drive shaft. It cured all the issues. By the time I did it it was a lot worse then when I wiggled the drive shaft when I started this thread. Quite clearly had lots of play in them instead of a hint of some. Lots of clunking at low speed shifts.

I really should have walked through the step by steps posted above. I kept needing to pull the caps back out because one or the other would have one needle bearing or more get tipped over when I slid the joint into one side or the other. The sign of that was that it wouldn't press flush to the rubber ring at the base of the cap and then I couldn't get close to putting the clips on both ends. I hate 30 minute jobs that take hours.

One thing that was odd was that at my local parts store the same Spicer U-joint could come in two different boxes and one joint was clearly smaller than the other. Same part# on the end of the box. I used the large version and it fit. If you use OReillys , keep that in mind.
 
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