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I have a '87 4.0 auto 2wd. It hasn't really been out of town for several months, and on the last road trip, aside from the cruise, it was fine.

 It now has a vibration above 60mph.

Naturally, I checked the u-joints.... they were fine, however the slip yolk moved a lot. Also, when I wiggled it there was a slight metallic clunk from the driveshaft.

then I noticed this....

 

 

( I noticed this after loosening the bolts :yes: )

While I did paint across the yolks, I did not put the arrow there.

It kind of looks like the driveshaft is maybe starting to separate, to me.

 

Has anyone had or noticed anything like this?

At first I was thinking just a new slip yolk, but now .... :dunno:

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The stock driveshaft on 2WD MJs has an encased rubber sheath around the inner shaft that supposedly helps prevent vibrations. It looks like the rubber sheath inside has deteriorated and the outer shell has shifted. I've never seen this shift before. I'd take it to a local driveshaft shop and try to have it balanced. When I tried to have my original shaft balanced the shop guy said the rubber was AFU inside and he couldn't balance it. I think you have a similar problem. I ended up having a new driveshaft made.

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The stock driveshaft on 2WD MJs has an encased rubber sheath around the inner shaft that supposedly helps prevent vibrations. It looks like the rubber sheath inside has deteriorated and the outer shell has shifted. I've never seen this shift before. I'd take it to a local driveshaft shop and try to have it balanced. When I tried to have my original shaft balanced the shop guy said the rubber was AFU inside and he couldn't balance it. I think you have a similar problem. I ended up having a new driveshaft made.

 

This. My 2WD driveshaft did the same thing.

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The stock driveshaft on 2WD MJs has an encased rubber sheath around the inner shaft that supposedly helps prevent vibrations.

 

Weird.  The two I have are not built like that.

 

Either way, if the u-joints aren't in phase then it will vibrate, and the shaft is effectively garbage.

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The stock driveshaft on 2WD MJs has an encased rubber sheath around the inner shaft that supposedly helps prevent vibrations. It looks like the rubber sheath inside has deteriorated and the outer shell has shifted. I've never seen this shift before. I'd take it to a local driveshaft shop and try to have it balanced. When I tried to have my original shaft balanced the shop guy said the rubber was AFU inside and he couldn't balance it. I think you have a similar problem. I ended up having a new driveshaft made.

 

 

 

The stock driveshaft on 2WD MJs has an encased rubber sheath around the inner shaft that supposedly helps prevent vibrations. It looks like the rubber sheath inside has deteriorated and the outer shell has shifted. I've never seen this shift before. I'd take it to a local driveshaft shop and try to have it balanced. When I tried to have my original shaft balanced the shop guy said the rubber was AFU inside and he couldn't balance it. I think you have a similar problem. I ended up having a new driveshaft made.

 

This. My 2WD driveshaft did the same thing.

 

 

I was worried it was the shaft. guess I need to find a shop.

 

Thanks for the help everyone :thumbsup:

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What do y'all mean by having the u joints in phase? I've never heard of that.

 

See Hornbrod's picture...  Anything other than the top example is not okay, even if the yokes are only misaligned by a few degrees (the 90* example in the lower part of the picture is the worst case scenario).

 

Reason being is that the shaft speeds up and slows down as the u-joints misalign, but this affect is canceled by the u-joints being in phase (the output, or pinion in this case, will not see a rhythmic changing of velocity).

 

The wikipedia entry explains what's going on better than I can, if you care to read it.

 

https://en.wikipedia.org/wiki/Universal_joint

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The nature of a u-joint is that when it's at an angle, the driven end will accelerate and decelerate as it goes around, even with the driving end at a constant speed. Fortunately it also works backwards, so using a second ujoint at the opposite angle will cancel out the change in speed and produce a constant speed at the other end of the driveshaft, so long as the second joint is a perfect mirror of the first. That's "in phase", the "yes" in Hornbrod's pic.

Any other position of the two joints relative to each other is "out of phase". In Hornbrod's pic, the "no" is a common error, the u-joints are identical but positioned identically, not mirrored to the other. This will amplify the accel/decel of the rotation of the end of the shaft (in this case the axle's pinion gear) producing... I'll call it sub-optimal power delivery to the wheels.

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When I went to the shop, he said he didn't know jeep ever used them & "that's 60's technology" he then said the one thing he could do with it was " throw it away"

 

It turns out my output  bushing is all but gone, so i'm going to get that done first.

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