Vibration in drivetrain

[thistle3585]

I got my Jeep put back together, having pulled the engine, Transmission and Transfer Case , and am noticing a vibration in the rear end. It is more pronounced in two wheel as opposed to four wheel, and more noticeable at about 30 mph, so I'm guessing it is the drive shaft. I thought the drive shaft was balanced and as long as I didn't separate it then it would go right back on regardless of the yokes. Would replacing the u bolts on the yokes resolve this or do I need to figure out how the drive shaft was originally positioned on the yokes? For what its worth, I do have spacers to reduce drive line angle which I had installed before I did the work.

 

[Saddle Tramp]

Yep the shafts are balanced and it is important to reinstall the driveline/axle yokes to their original relationship or you can experience vibrations. Try disconnecting the driveline at the rear end and rotating it 180 degrees, which may be all that is needed. Always mark the yokes before you pull the drive line. Also check to make sure the U-bolts are seated properly.

 

[gert]

You can also take the drive shaft to a shop and have it balanced that might help the factory balanced the drive shafts while running the jeep(much better). Look at you motor mounts and Transmission mount make sure they are not worn out as that will transmit vibrations Also what is your pinion angles set to? If it is still stock then it should be good but if you have a lift kit on it you might need to reset your pinion angle

 

[73CJ]

A couple things to concider

Good ujoints?

Ujoints seated properly?

Ujoints in phase?

Did you lift the Jeep?

That's another story. The driveshafts need to angled equally at each other.

Lots of posts on here about that

 

[BusaDave9]

Did you take the drive shaft apart at the spline? A u-joint speeds up and slows down with each rotation.

This causes a rotational vibration. If the drive shaft is angled properly the vibration of the front u-joint will cancel out the vibration of the rear. For this to happen both yokes of the driveshaft must be at the same angle and NOT 90° off. This drive shaft is correct. You can tell because the 2 clips on the ends of the 2 u-joints are on the same side. not 90° out:

Also the angle of the front u-joint must match the rear. This is what 73CJ was talking about.
Am I making sense? I am talking about 2 different angles. The yokes must match (not 90° out, this you can tell even when the driveshaft is removed) and the tilt of the front U-joint must match the rear.

You don't have a double cardan joint, do you?
It may not be the driveshaft. Try rotating the tires - front on rear and visa versa.

 

[thistle3585]

Maybe a 1-2" lift when I replaced the springs but I added spacers on the Transfer Case plate to reduce the driveshaft angle. The yokes match up properly. I'm going to be swapping the rear axle out in the next week or two, so I'll wait until I do that and see where I stand. Since I had pulled the whole drive train, I get the impression I should go back and check my nuts and bolts for tightness.