U-joint/yoke issue?

MomoJeep

Basic User
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City
Seattle
State
WA
#1
After wheeling in lots of sand/dust and harsh washboard roads, Jeep got a vibration at highway speeds. So I got the tires re-balanced. That helped, but still some shimmy. So I checked axial play in rear driveline. The u-rear u-joint moved side to side a bit on one of it's axes. So I figured it needed replacing. Took driveshaft out (straps holding it in, not u-bolts). After removing it I couldn't see anything wrong with the ujoint. From cup to cup it's supposed to measure 3.219. My dial calipers show it to be pretty much 3.219 +/- 1 or 2 thou. So I put it in the vice to put inward pressure on bearing cups. Still ~3.219". The cups so wiggle a bit, but not sure that's an issue? There is grease in them, although it's probably a bit dirty. And the u-joint is only 2-3 years old. the previous one lasted 6+ years. So then I measured the width between the two little axial retention tabs on the yoke. I get anywhere from 3.220 to 3.225. Slight larger.

So is the U-joint bad or did the yoke somehow get widened?

Maybe the straps don't hold as tight as u-bolts would have, allowing some movement with wore down on the retention tabs?
 

rubclt

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Charlotte
State
NC
#2
I read about your joint, not sure, another thought... did you check the pinion yoke, does move or leak? Could be pinion bearing causing vibration too... good luck tracking down issue
 

ag4ever

Average Nut
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CJ-8.com Member
City
Richmond
State
TX
#3
U-Joints don’t usually wear on the ends of the cups, it is the needles in the cups and the circumference of the inner cups that wear. If the cups rock at all on the u-joint they are toast.

As cheap as a U-Joint is, I’d replace one if I thought it MIGHT be bad, even if it is not bad.
 

spankrjs

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City
Biloxi
State
MS
#5
I have cracked one of the little "tits" that holds the u-joint tightly in the yoke. Happened the first time I was in Moab when I spun a rear axle tube. Never noticed it. Drove it home, then to Michigan. Had a slight vibration on the way home. U-joint could move just a hair left and right. Had to install a new yoke and U-joint to fix it.

Post #1068:

https://www.cj-8.com/threads/anothe...trip-update-body-on-frame-again.24692/page-54
 
Last edited:

MomoJeep

Basic User
CJ-8.com Member
City
Seattle
State
WA
#6
Thanks guys. The pinion bearings are fine, the yoke does not move side to side nor is it leaking. Yes, I'll probably just replace the joint anyway, but my concern is if the yoke retention tabs have worn to allow the U-joint to go off center and repeatedly simmy back and forth when driving. Thanks Spankrjs for your input on that. But I also think some high-torque situations could push a cap outward under the strap (not u-bolt) and put it out of alignment. The retention tabs seem to be about 0.004" wider than the u-joint spec dimension of 3.219".

Question: Is being .004" out on one side enough to cause a vibration?
 

Randyzzz

Blown Budget
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City
Redmond
State
OR
#7
Thanks guys. The pinion bearings are fine, the yoke does not move side to side nor is it leaking. Yes, I'll probably just replace the joint anyway, but my concern is if the yoke retention tabs have worn to allow the U-joint to go off center and repeatedly simmy back and forth when driving. Thanks Spankrjs for your input on that. But I also think some high-torque situations could push a cap outward under the strap (not u-bolt) and put it out of alignment. The retention tabs seem to be about 0.004" wider than the u-joint spec dimension of 3.219".

Question: Is being .004" out on one side enough to cause a vibration?
That would be a question for a driveline shop. But- I do know that all my u-joints are a snug- real snug- fit between the ears. If you decide to replace the yoke, I would upgrade to the style that used the two small u-bolts instead of the straps.
 

CJ-8_Jim

Scrambler Junkie
LIFETIME
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City
NW Chicago Suburb
State
IL
#8
Another diagnostic step to consider: Before you bolt the driveshaft in, take it out completely and drive in FWD only to determine if the vibration is still there. That would confirm that the vibration is related to the rear drive shaft.
 

spankrjs

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City
Biloxi
State
MS
#9
Like Randyzzz said, the u-joint should be a snug fit to the yoke, no side to side movement. You shouldn't have to beat the u-joint into the yoke, you should be able to push it in by hand, but it should be snug. Always dig all the gunk/mud/grease/sand out of the yoke when reinstalling the u-joint/driveshaft.

I will agree to disagree on the u-bolt style yoke being stronger then the strap style yoke :twocents: :evil: :thumbsup:
 

Randyzzz

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Redmond
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OR
#12
I agree the U-bolt fastener is stronger than the straps. You do need to be careful not to over tighten them though.
I know there are different qualities of u-bolts as there are straps. I got some Chinesium u-bolts and stripped them out with basic tightening. I reinstalled the old factory ones- no problem.
I do know there are aluminum “girdle” style straps that are much stronger.
 

MomoJeep

Basic User
CJ-8.com Member
City
Seattle
State
WA
#13
New question: When putting the new U-joint into the driveshaft, the cap on one side literally slid into place with very light finger pressure. I do not think it should be this loose. It's "snug" but no longer a "press fit". Is this a problem?
 

Randyzzz

Blown Budget
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City
Redmond
State
OR
#14
New question: When putting the new U-joint into the driveshaft, the cap on one side literally slid into place with very light finger pressure. I do not think it should be this loose. It's "snug" but no longer a "press fit". Is this a problem?
It should be a press fit. Sounds like that ear is loosening up.
 
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