No U-joints?

omnitonic

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While under my new Jeep installing the exhaust, I got my first good look at the driveline. There are these weird doodads on either end of the shaft running from the transfer case to the rear diff. They look like maybe rag joints? I did a little web searching, and my google fu has failed me today, so I thought I'd just start a thread and ask. What dark magic is this? What ARE these things?





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LittleDog

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While under my new Jeep installing the exhaust, I got my first good look at the driveline. There are these weird doodads on either end of the shaft running from the transfer case to the rear diff. They look like maybe rag joints? I did a little web searching, and my google fu has failed me today, so I thought I'd just start a thread and ask. What dark magic is this? What ARE these things?

CV (constant velocity) joint. I think JKs had them too.

Stronger, and work better at greater angles, so less need to mess with for lifts, but no replacing them in the field.

Saharas have them on the axle too, with Selec-trac. Not exactly sure why, nor sure about other sub-models. Might have to check the boots after many years, but turns smoother, anyway.

You can replace them with U-joints, but that's personal preference.
 
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omnitonic

omnitonic

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CV (constant velocity) joint. I think JKs had them too.

Stronger, and work better at greater angles, so less need to mess with for lifts, but no replacing them in the field.

Saharas have them on the axle too, with Selec-trac. Not exactly sure why, nor sure about other sub-models. Might have to check the boots after many years, but turns smoother, anyway.

You can replace them with U-joints, but that's personal preference.
Very interesting! I'll have to do some deeper research into this. I've never had a CV boot or CV joint go bad, so I've never actually messed with or seen a CV joint. These don't have boots, and seem kind of exposed.

I put an overdrive auxiliary into a '77 F350, which required extensive dicking around to get the driveline angles within acceptable tolerances, and I have changed more than my fair share of U-joints. I think I'll keep'em stock and see what happens over time.

Thanks for the illumination!
 

americonium

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Rzeppa joints. I put a 2.5 inch lift on my JK, went rock crawling, and blasted them to smithereens. Replaced the driveshafts with Adams and never looked back.
 

LittleDog

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Very interesting! I'll have to do some deeper research into this. I've never had a CV boot or CV joint go bad, so I've never actually messed with or seen a CV joint. These don't have boots, and seem kind of exposed.

I put an overdrive auxiliary into a '77 F350, which required extensive dicking around to get the driveline angles within acceptable tolerances, and I have changed more than my fair share of U-joints. I think I'll keep'em stock and see what happens over time.

Thanks for the illumination!

I've had wheel CV boots go bad a year apart on a different vehicle, but that took about fifteen years of New Jersey winter salt.

Not sure about these bootless ones on the drive shaft, but I guess we'll find out.
 
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omnitonic

omnitonic

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It looks like the big advantage is that they are more tolerant of driveline angle variations. Good thing to equip on a vehicle where a significant percentage of your customer base is going to lift the thing. In theory. In practice, the stock axle CV joints are prone to grenade, as in the video I linked.

I do get the point though. When you don't have the optimal angle with U-joints, it's very apparent that they are NOT constant velocity. They aren't constant velocity at the optimal angle either, but it's much less apparent that the driveline is speeding up and slowing down constantly.

The CV joints stock on the driveshafts do have boots. They're just small and less obvious than the huge boots on a front-wheel drive car. If they deteriorate, the joint will grenade eventually. It's a good thing I'm aware of this, and know to monitor these! Jeep world sure has a lot of things for new owners to figure out.

Adams driveshafts do seem to be a good way to go, but I have seen no reports of trouble in vehicles that were not lifted, so this is something to keep in mind for later. My Jeep is already enough of a money pit, and I've had to pick and choose the minimum essential upgrades.

I'm not likely to lift it and put on bigger tires anyway. I would really want to regear if I did, because I can barely tolerate the stock 3.45s with the stock tires as it is. Now I know I would also really want to address these CV joints too. I'd probably end up getting into the upgrade to the tune of $5,000, and there would still be a guy out there with more clearance and more flex than me anyway. I am better off leaving Pandora's box closed.

For now :LOL:
 

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If all aftermarket replacement driveshafts that I’m aware of utilize a double cardan U-joint specifically for the purpose of accommodating the greater driveshaft angle of a lifted suspension, how is it that the rzeppa joint OEM shafts are supposedly better at greater angles or more tolerant to driveline angle variations? I truly don’t understand that thought.
 
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omnitonic

omnitonic

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If all aftermarket replacement driveshafts that I’m aware of utilize a double cardan U-joint specifically for the purpose of accommodating the greater driveshaft angle of a lifted suspension, how is it that the rzeppa joint OEM shafts are supposedly better at greater angles or more tolerant to driveline angle variations? I truly don’t understand that thought.
Standard U-joints are finicky. I went through hell working out where to put the transmission hanger bracket on that old Ford after I inserted an auxiliary transmission into the driveline. The rzeppa CV joints would have made that a cakewalk.

They're fine for moderate lifts, which is probably what most customers get. Equipping the double cardan U-joints would probably cost a lot more, and it's a matter of averages.

Or maybe they're just cheap assholes for equipping these garbage CV joints that can't tolerate lifts. I'm not saying they're a good thing, I'm just saying I can see Chrysler's thinking on this one. I can't afford to lift my Jeep anyway. New axles, a regear, a lift, AND new tires. My budget isn't that big. So I am okay for the foreseeable future. The CV joints seem to be fine for stock ride height.
 

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