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Unread 06-26-2012, 02:40 PM   #1
Colt44
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Vibration = U-Joint?

Everything was running along smoothly... it was too good to last, of course.

I'm getting a noticeable vibration now, under power and especially when accelerating up through 40-60 MPH. Not as noticeable under steady power, except it seems to persist somewhat at higher speeds.

I can't really hear it, but I can feel it through my hands, feet and butt.
It's not a very rapid vibration and doesn't seem to be in time with engine rpms, so I'm thinking U-joint on the rear drive shaft. (Not using 4WD and hubs are free.)

There are two U-joints, of course; one at each end of drive shaft.
How to diagnose if this is the problem, and how to tell which one needs replacing?

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Unread 06-26-2012, 02:43 PM   #2
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Quick way is to get under it and grab the drive shaft then move it. If it moves a lot replace the joints. While under there it wouldn't hurt to put some grease in the shaft and joints.
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Unread 06-26-2012, 02:47 PM   #3
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You can look for more play at one joint or the other if you really just want to do one.

IMHO, if one is gone, the other can't be far behind. As such, its not a bad idea to do both at the same time (and it saves you from doing the same job again in a week). Also, the 'better' old joint can be carefully put back in a box and make a nice emergency spare for your trail box.
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Unread 06-26-2012, 02:48 PM   #4
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Quote:
Originally Posted by Colt44 View Post
Everything was running along smoothly... it was too good to last, of course.

I'm getting a noticeable vibration now, under power and especially when accelerating up through 40-60 MPH. Not as noticeable under steady power, except it seems to persist somewhat at higher speeds.

I can't really hear it, but I can feel it through my hands, feet and butt.
It's not a very rapid vibration and doesn't seem to be in time with engine rpms, so I'm thinking U-joint on the rear drive shaft. (Not using 4WD and hubs are free.)

There are two U-joints, of course; one at each end of drive shaft.
How to diagnose if this is the problem, and how to tell which one needs replacing?
Your profile says yo are stock. Sounds like a bad u-joint. Get under the jeep with the wheels chocked on level ground (be safe) and put the jeep in neutral (key off of course). Grab the DS and twist, push, pull, etc and look for movement/slop in the u-joints and slip-joint. Hand snug up the joint strap bolts if any are loose. If the joints appear to be worn, pull the shaft and take it to your local DS shop. Have them put genuine Spicer U-joints in. If the slip joint is loose you may need it repaired. This whole deal could run you from $75-200 for the repairs. If you are lifted 4" or more, you probably need a CV shaft to cure the vibe regardless of the condition of your old DS.
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Unread 06-26-2012, 03:50 PM   #5
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Also check the yokes for any movement. The later strap style has a tab that secures the ujoint from moving. But a bad ujoint can snap that tab and cause even more movement and vibration
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Unread 06-27-2012, 08:21 AM   #6
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Thanks for the info. If one is worn, I'll probably just replace both.

Why would Spicer have to be done at a specialty shop?

ETA - driveline is all stock, and no lift.
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Unread 06-27-2012, 10:06 AM   #7
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Originally Posted by Colt44 View Post
Thanks for the info. If one is worn, I'll probably just replace both.

Why would Spicer have to be done at a specialty shop?

ETA - driveline is all stock, and no lift.
I don't think anyone mentioned a specialty shop. Just make sure the DS shop uses Spicer u-joints and not China crap. Of course, if you want to do it yourself you can, but why? The DS shop does this work fast and fairly cheap and they will throw it on a balance machine to test it before you take it home. That way you know its not bent or out of balance.
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Unread 06-27-2012, 10:11 AM   #8
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If a shop only does driveshafts, doesn't that make it a specialty shop?
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Unread 06-27-2012, 10:16 AM   #9
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I have a $150 shop press from summit and it makes U-joints as easy as an oil change! Spice doesn't have to be done at a shop. Which leads me to my next point, I had the same vibration at the same speeds. If i barely had my foot on the throttle, the vibration would go away, otherwise I could feel it and not hear it at all. Funny thing is, I had just pulled my U-joints, cleaned them up, greased them, and put them back in, they looked and felt great. Then the vibs happened. I checked the oil in my tranny and t-case. Come to find out my Dana 20 had NO oil. I had just purchased the jeep and only driven it 50 miles or so. Thanks PO. I bought the NOVAK rebuild kit and am halfway through the rebuild. I also sand blasted the case to paint it DupliColor cast iron. Enter project kreep. Now I'm painting my T-18 and replacing my rear main on the 304, and cleaning the block, and and and...

Summary, check your t-case and tranny oil. I haven't finished the rebuild, so I'm not sure it was the t-case, but it cant hurt to check.
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Unread 06-27-2012, 10:18 AM   #10
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Quote:
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If a shop only does driveshafts, doesn't that make it a specialty shop?
I'm not sure what your point is but I never said Spicer u-joints would have to be done at a specialty shop. U-joints are u-joints as far as installation goes. I was just giving you a heads-up to look out for shops that install quality u-joints as opposed to China crap.
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Unread 06-27-2012, 10:23 AM   #11
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Quote:
Originally Posted by Outnumbered View Post
I'm not sure what your point is but I never said Spicer u-joints would have to be done at a specialty shop. U-joints are u-joints as far as installation goes. I was just giving you a heads-up to look out for shops that install quality u-joints as opposed to China crap.
Okay, now I understand what you meant, and I'll make sure to ask about using the Spicer parts - I try to use the best when I have to replace something.

To me, a shop that does many types of work, like a normal mechanic, would be a general shop, so to speak.

Someone who only does transmission, or brakes, or... drive shafts, would be a specialty shop.

What is your definition of "specialty shop?"
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Unread 06-27-2012, 11:12 AM   #12
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Right-on, let us know how it works out.
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Unread 06-27-2012, 11:59 AM   #13
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Right-on, let us know how it works out.
Will do, but seriously, what do you consider to be a specialty shop?
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Unread 07-01-2012, 05:58 PM   #14
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It was indeed the u-joints. Both of them. One was pretty much shot and the needle bearings in the other were disintegrating.

No Spicer parts readily available in Memphis (town's only a million people) so went with good ol' NAPA.

Running smoothly again and waiting for the next problem to present itself.

As always, thanks for the advice.
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Unread 07-01-2012, 08:45 PM   #15
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Will do, but seriously, what do you consider to be a specialty shop?
What's the point? Just let it slide, OK.
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