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

734 Views 17 Replies 7 Participants Last post by  Boojo35
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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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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Worn U-joints can and will clunk. Keep pressing forward.
 

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Good to hear that you fixed it.
 
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