OEM rear driveshafts, is the yoke and DS balanced together? Vibrations - JeepForum.com
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post #1 of 5 Old 10-04-2020, 11:39 AM Thread Starter
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Location: Huntington Beach
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OEM rear driveshafts, is the yoke and DS balanced together? Vibrations

Long story behind the "WHY" but I have a driveshaft out of a KJ liberty and the slip yoke from a 242D/D44a/4.7 config WJ. I have a vibration at around 35mph that goes away and comes back at 70. The KJ driveshaft has a weight for balancing on it, the slip yoke does not. Since I swapped slip yokes, do I need to rebalance this driveshaft? Or are they separately balanced? Wouldn't an off-balance constantly vibrate instead of just at 35mph and 70?

What I've tried:
New u-joints (1330 at the yoke and a 1330/1310 conversion u-joint at the axle).
Axle pinion angle within 1 degree of TC output angle.

4" lift IRO long arm w/crossmember in front and adj shortys in the back.
newly rebuild 242D and D44a
front driveshaft removed
KJ liberty DS length is the same length as 242D/D44a WJ driveshaft but uses a 1330 u-joint at the axle. Stock WJ has a 1330 at the slip yoke and 1310 at the axle.

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post #2 of 5 Old 10-04-2020, 11:52 AM
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They are balanced as an assembly. Any driveshaft shop can balance the driveshaft for you. Another problem that can cause vibration issues on old driveshafts is when the splines get worn in the slip yoke. The driveshaft shop can also check that for you. The only solution for that is to weld in a new slip yoke.

One other thing to consider, especially with your 4-inch lift, is u-joint angles. A pair of U-joints on a shaft need to operate on the same plane or they will induce vibration. It could be that you need to adjust the pinion angle in the rear so that the u-joint angles at both ends of the shaft are parallel.

Here's a short video from Dana that explains it and shows the problem in action:
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post #3 of 5 Old 10-06-2020, 05:07 AM
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the other possibility is you got the U joints are out of alignment with each other when you swapped the slip yoke over
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post #4 of 5 Old 10-06-2020, 07:17 AM
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I will just throw it out there ... unbalanced tires will behave just like your description.

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ok mostly just repairs, but we are closing in on a lift
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post #5 of 5 Old 10-10-2020, 12:10 AM
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Originally Posted by CarlJH View Post
the other possibility is you got the U joints are out of alignment with each other when you swapped the slip yoke over

X2, the slip yoke "ears" must be in complete "phase" with the "ears" on the other end of the driveline, or the U-joints will be flexing at different times causing vibrations. Sight down the driveline from one end to the other, and make sure the "ears" line up with each other.

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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