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Discussion Starter · #1 ·
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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How did you check the u-joints? Just rotating the drive shaft won't show a problem. You have to force them rotationally and side to side. Put the Jeep in gear so the drive shaft can't rotate, then force each end in all directions. If it has a SYE/CV, also check the slip joint in the shaft center.
 

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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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You could temp remove the front shaft and see if the problem goes away. Stock YJs don't have a 'Slip Yoke Eliminator/Constant Velocity' drive shaft, just two normal u-joints front and back.

Here is the front end of my drive shaft. Ignore the disk brake, it's the red part with the double u-joints that is the CV part. It's a complicated assembly, can wear out and cause your problem, if you had one.
Motor vehicle Gas Automotive tire Vehicle Automotive exterior
 

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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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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!
True, it shouldn't turn in 2wd. As a test to see if the CAD is working right and is indeed disconnected in 2wd, while parked in 2wd, does the front drive shaft turn by hand?If it does not, then the CAD is connected and the front shaft is turning all the time when driving in 2wd.
 

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I would look into changing the differential fluid, its cheap and we mostly don't change it often enough. Look for metal, fine metal dust in the oil. Nothing there, nothing lost. I have had all kinds of vibrations start there, clutch pack with one broken friction clutch, pinion gear bearings, etc. lots to consider in that case. Axle bearings? Never felt the damage but it is a bad feeling when you are to late.
 

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Over the last week or so, the Jeep has developed a vibration that is not in the engine. . I can take it out of gear and rev the engine 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.

John
See bolded... perfect description of bad joints in rear. 99% sure it's the U-joints. Like Don said, taking the front D line off is just a way of eliminating the front being the cause. Doesn't sound like that to me. However, your Jeep is old. Joints wear out. Time to change them.
 
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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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Change your rear driveshaft U joints. If I remember right with the stock driveshaft there is only one.
The fact that the vibrations go away when there is no load pretty much says it all.
If you have a place that does drive shafts in your area they will do it for cheap and balance it too.
 

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Stock D line is a slip yoke style, but still has 2 joints. 1310 IIRC. 🙂
 
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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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I believe that you are on the right path if you are going to replace the U-joints.

Driveline vibrations from the output of the trans up to the pinion gear happen at 3, 4 or 5ish times the speed of a wheel vibration. It is dependent on the final drive gearing. Your drive shaft turns much faster than your wheels do though.

Driveline vibrations often feel fluttery for lack of a better term and are commonly load induced as you describe. They often times come with a droning type of noise or sensation.

As far as inspecting u-joints. They more often then not will feel tight with the wheels on the ground because the weight of the jeep and it being held in park, neutral, whatever...... it really does not matter but the shaft will be preloaded in one direction or the other if the wheels are not in the air and can easily mask any play in the joints. Good joints have no play whatsoever that is discernable to the naked eye. Some bad u-joints have no play in them at all but if you remove the drive shaft and move the joints through their range of motion you will find that they may bind or not want to move at all in a certain direction. Ones like this will certainly vibrate and when they are removed they generally have insufficient lube and galling inside the caps where the needle bearings ride.

When you install new joints, they need to move freely. I personally do not use a press as it can bend the ears of yokes or shafts in somewhat and create a binding condition with a new u-joint. I have an XJ in the shop that I am installing new u-joints tomorrow. I need to remember to take pics and maybe a video of how I do them. I am picky about how to take them out and install them to prevent binding and bending.
 

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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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Worn U-joints can and will clunk. Keep pressing forward.
 

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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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Good to hear that you fixed it.
 
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