Bent belly skid and driveline vibrations


SvtLdr

Just a guy, with a Jeep
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I adjusted the pinion angle. Best I can measure it's about 0.8*.

View attachment 258267

Vibes are the same. I rotated the tires and no change there.

Vibes are definitely more pronounced under load. Going up hill the vibes are much worse than coasting down hill at the same speed.

In 4wd the vibes are less. Not sure what to make of that. May be reduced load on the rear driveshaft.

I guess next step is the pull the rear driveshaft to confirm that's the problem and inspect as best I can.
You mentioned that you rotated the tires but did you have the tires balanced also?

I'm interested in what you find here as I'm dealing with a similar situation.
 
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srimes

srimes

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You mentioned that you rotated the tires but did you have the tires balanced also?

I'm interested in what you find here as I'm dealing with a similar situation.
no just swapped front to back, flipping l/r on the rear. Idea is that if the unbalanced tire is in the front I'd feel it in the steering wheel, but I never did. Also a good thing to do to keep tire wear even, so I figured it was worth doing either way.
 
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srimes

srimes

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I took the driveshaft off and went for a drive, and the vibes were gone.

The driveshaft seemed tight and I couldn't feel any slop in the joints, but when I spun the caps (that went to the pinion) they felt just a little gritty, so I'm thinking I should replace at least that one and see if that fixes the vibes.

It makes sense that it would be worn as the pinion-driveshaft angle was off 6-7 degrees.

Do you think I can keep the double joint u-joints? I'm thinking/hoping that they should wear less as they weren't out of alignment.

All the joints are greaseable. The pinion u joint measured 1.063 x 3.618, I take it that's a 1330 series. Which one should I get? I'm thinking spicer sealed/non-greasable. What's the best source? Last time I rebuilt a driveshaft it had to hunt to find spicer joints.
 

SvtLdr

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Just to be clear, you're talking about the REAR driveshaft, right?

If it were me, I'd replace all three U-joints at the same time. Unless, you really enjoy doing the work and just want to tear the shaft apart again in the near future. lol

Correct, that sounds like a 1330. Here's a source I've used before for good prices on Spicer joints. Denny's Driveshaft in Kentucky. The shipping to Oregon may be a different story though...

I really like the greaseable joints because I'm a fan of maintenance. Other's prefer to not have to worry about it and use sealed joints. It's really personal preference.
 
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srimes

srimes

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Measured as best I could with the joints still in the driveshaft and they're defiantly not all 1330. 1310 makes more sense as those are the factory sizes.

I have a rear Dana 44 and it looks like the rubicons used a 793x, but that's 1.125, while mine measured at 1.063, which would be a 5-134x.

Is it possible they installed the wrong ujoint? Seems like the vibration would be terrible right away if they did that.

Guess I need to crawl back under and try to measure the yoke at the axle.
 

pagrey

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You are smart to get in there and measure them, that's probably the best way. A shop could have made just about anything work so there's no guarantee the stock replacements will be the correct ones. There's no way you could have the wrong joints installed, I think they wouldn't fit at all.
 
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srimes

srimes

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p.s. Local there's only MOOG and SKF versions of the 793X. It'd be nice to support local and have the option for quick buy and possible return if it's the wrong size, but I've always heard to stick with spicer.
 

pagrey

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Personally it's only the front axle u-joints I'd worry about with respect to strength but everybody has different needs. I ran Moog in the front and they wore out quick but for the driveshaft I wouldn't worry.
 
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srimes

srimes

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Personally it's only the front axle u-joints I'd worry about with respect to strength but everybody has different needs. I ran Moog in the front and they wore out quick but for the driveshaft I wouldn't worry.

OK thanks. Makes sense there's less stress on the driveshaft and much easier access too.

I checked the pinion and confirmed that the u joint is sized correctly, so I guess it's a 134x. That wasn't listed in the chart of TJ u joints so I wonder what's up with that. It sure looks like a TJ Dana 44. I sure hope the chromo shafts I just bought for them fit.