Rear driveshaft u-joint issue

[jeeper99]

So my 99 TJ had a 3" lift on it when I bought it in May. It's driven fine since then until it recently developed a vibration (in the steering wheel; trans and t-case shifters didn't move) mostly in 2nd and 3rd gear with a rhythmic, but not very noticeable vibration in 4th and 5th. After researching it appeared to be a u-joint issue. There was no movement in the rear driveshaft, but I still took it out and took it for a short drive in front wheel drive. The vibration was gone.
So I changed out the rear u-joint in the driveshaft which did have some movement inn the two pinion that attached to the axle yoke (see pic). Put in a new Spicer 5-153x and the first couple drives were good. Now the vibration is back, exactly the same way with just a little less intensity. The new u-joint is move and right in the driveshaft, but the cross moves side to side in the caps that are strapped in the yoke. The caps themselves do not move and are mounted in the yoke properly. So why is the cross moving? That's the question.

 

[Mike_H]

Something isn't pressed together correctly. I think you'll end up replacing it again. The cross shouldn't slide in and out of the caps.

 

[Tigerman]

So my 99 TJ had a 3" lift on it when I bought it in May. It's driven fine since then until it recently developed a vibration (in the steering wheel; trans and t-case shifters didn't move) mostly in 2nd and 3rd gear with a rhythmic, but not very noticeable vibration in 4th and 5th. After researching it appeared to be a u-joint issue. There was no movement in the rear driveshaft, but I still took it out and took it for a short drive in front wheel drive. The vibration was gone.
So I changed out the rear u-joint in the driveshaft which did have some movement inn the two pinion that attached to the axle yoke (see pic). Put in a new Spicer 5-153x and the first couple drives were good. Now the vibration is back, exactly the same way with just a little less intensity. The new u-joint is move and right in the driveshaft, but the cross moves side to side in the caps that are strapped in the yoke. The caps themselves do not move and are mounted in the yoke properly. So why is the cross moving? That's the question.View attachment 65593

My 2 cents...

Like Ranger_b0b said, if the cross in the u-joint slides right and left it is not pressed in correctly. That is a cause of the driveline vibration at any speed, but... The 4th and 5th gear vibration you are describing is cyclic (harmonic) and the u-joint is not the culprit. My guess is that the harmonic vibration was always there for you, but you never paid attention to it until now. To fix that one you have to fix your pinion angle.

 

[jeeper99]

Ok, got the driveshaft off. It measured 3 5/16" inside the "ears" and when I put the driveshaft back in, I noticed that the play isn't in the cross, it is the caps in the axle yoke. There's a 1/16" gap between the ear and cap when fully seated on the other side. So it would appear the yoke is a little stretched. Either way, I do agree that I'm going to have to fix the pinion angle. Here's how it sits now, also had a ~1" t-case drop that was also on it when I bought it. Should I go sye/adjustable control arms or mml/bl, or both/some sorry of combo? I'm thinking the sye/aca, despite the price. [emoji849]

 

[MutantNinjaTJ]

How did you get the old ones out? Hammer or press? The press may have stretched the yoke if not correctly supported, same with using a hammer to beat them out, you may have damaged the yoke.

 

[jeeper99]

It's the two caps that are in the axle yoke, held in by the straps. I didn't have to pound/press them. Just the ones in the driveshaft itself, but they're not loose. Apparently the axle yoke has stretched for since other reason, maybe due to the pinion angle, which may have caused enough vibrations to slowly widen it over the last few months.
The lift has been on it for longer than that. The PO bought it like that and had had it about a year or so before I bought it back in May. He had it long enough to change out the shocks, though I don't recall him saying if it was because they were old or just rode rough.

 

[AndyG]

I’d make sure you got the correct u joint in the box.