Attention Drive Shaft gurus

I had a double cardan driveshaft made up about 1 year ago. It has always vibrated and I have tried every thing. I am at 6" in the back and 5.5 in front. I took the front shaft out and put in in the back and no more vibration. Easy you say must be DS. Well I have had it rebalanced twice and retubed once and they tell me it balanced up real nice on their machine. I am going to try to take it back and get a secondhand front shaft and get it lengthened.

Question is why would a front shaft with spicer gear not vibrate and a shaft with non genuine spicer gear vibrate.

Considered that the shop you're seeing doesn't really do a good job?


Most of the places that are local to me (wait, all) don't balance their driveshafts. They throw them on the lathe and do a runout check. If it's within say .005 they call it good enough and tell you it's balanced. If you complain that it vibes they say that there must be something wrong with your vehicle. They actually can do a pretty good job with this method, but it only goes so far.



But, what do I know. Mine are made of pipe. And I got the runout within a half inch and quit. And they definatly aren't balanced. But at least they aren't square.

How old are the joints in the DS? Have they been replaced? Not to say that your choice of shops is bad but is there another one that you could go to to get a 2nd opinion?

The DS was new 12 months ago and has vibrated since day 1.

are the u-joints in phase with each other? By that I mean is the slip joint splined together at the right place so the front joints and the rear joint are aligned evenly? It'll vibrate if they aren't.

96XJay said:

are the u-joints in phase with each other? By that I mean is the slip joint splined together at the right place so the front joints and the rear joint are aligned evenly? It'll vibrate if they aren't.

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Its a double cardan shaft. The ujoints cant be out of phase. If it were a single cardan shaft, that could be a posibility.

The front shaft is quite a bit lighter than the one that I have in the rear. The rear shaft first makes a rumble at about 35mph. The vibration is felt from about 40mph up.When I put the front shaft in the rear I could tell it was better before I had gone 100 yards. There is no vibration or noise with the front shaft in the back even at 75mph.

I also am suspicious of the no name double cardan that is in the back.

Doesnt say much for the way the shop is balanceing it.

Ray H said:

Its a double cardan shaft. The ujoints cant be out of phase. If it were a single cardan shaft, that could be a posibility.

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My bad. Thanks for the correction.

Ray H said:

Its a double cardan shaft. The ujoints cant be out of phase. If it were a single cardan shaft, that could be a posibility.

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Not true,they still have to be in Phase with the rear(axle) joint.Anything other than "Perfect" will cause a vibe!

That's what I thought. Just didn't feel like arguing.

RCP Phx said:

Not true,they still have to be in Phase with the rear(axle) joint.Anything other than "Perfect" will cause a vibe!

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The whole point of a double cardan is to eliminate the phase that single cardan joints have. A double cardan is nothing more than two ujoints that offset each others phase. The single ujoint at the pinion should be lined straigth up the shaft so, ideally, it wont have a phase either.
So, the double cardan eliminates the phases of the top joint and the bottom joint has no phase because its straight, hense, no phases using a double cardan shaft.

You dont have to believe me, actually you dont have to believe anyone, but here it is in writing (other than mine)http://www.buildyour4x4.com/index.php?id=47

Ray H said:

The whole point of a double cardan is to eliminate the phase that single cardan joints have. A double cardan is nothing more than two ujoints that offset each others phase. The single ujoint at the pinion should be lined straigth up the shaft so, ideally, it wont have a phase either.
So, the double cardan eliminates the phases of the top joint and the bottom joint has no phase because its straight, hense, no phases using a double cardan shaft.

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This is right. The most important point is to get the rear pinion pointing pretty much at the output of the tcase. Ideally it should be about a degree lower to compensate for torque loading.

Another trick is to put the rear driveshaft on the front and see if the vibes follow. If they don't it is pretty much a sure thing that the pinion angles are off.

Just for the sake of discussion.... If one's pinion angle was off a few degrees and the joint was not lined up with the others do you not agree that this could cause a phasing problem? I see how it hypethetically would not cause a phasing issue if it was pointed straight towards the output of the case (0* pinion angle) but... Let's for a second assume that it is off just a tad by a few degrees, which is likely in many cases.

96XJay said:

Just for the sake of discussion.... If one's pinion angle was off a few degrees and the joint was not lined up with the others do you not agree that this could cause a phasing problem? I see how it hypethetically would not cause a phasing issue if it was pointed straight towards the output of the case (0* pinion angle) but... Let's for a second assume that it is off just a tad by a few degrees, which is likely in many cases.

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I agree that it would likely cause vibes but I wouldnt say its "out of phase". Double cardan joints are constant velocity joints so they have no phase (or lead/lag).To me "in phase" with another joint would mean that the lead in one joint would be in sync with the lag in the other joint. Since double cardans have no lead or lag theres nothing for the single cardan to be "in phase" with. It would simply go through its velocity changes as it spins, with nothing to off set it, causing vibes. I would consider that situation as a misalignment more than a phase issue.

Makes sense. Too much thinking though. It's making my head hurt. Well for the heck of it I'll always run my rear joint on my CV driveshaft in line with the front joints just in case it has an effect. I'll take it out of the equation.

Ive always wondered why these guys with 6+" of lift arent running driveshafts with two CV joints, not so much on XJs but on SWB Jeeps especially. That would be a true high angle DS. I mean the rear DS on a TJ/ YJ or CJ is only about 25" long. If you have 6" of lift or more, that DS and pinion is at a steep angle. I cant think of a reason, besides ground clearance or maintenance, that you couldnt help manage that angle better by using a DS with two CV joints. You could set your pinion angle however you want and not have driveline angle issues. The same would go for trying to manage the front driveline angles while maintaining good caster.

Well I have tried it 90 degree out and it is actually better. Still doesnt help me though.

I think you'll probably end up taking it somewhere to get it balanced properly or replacing it. If your ujoints are in good shape, your angles are right and the front shaft works well in that position, it sounds like balance.
How about the slip splines on the shaft, is that it good shape, nice and tight?

Ray H said:

Ive always wondered why these guys with 6+" of lift arent running driveshafts with two CV joints, not so much on XJs but on SWB Jeeps especially. That would be a true high angle DS. I mean the rear DS on a TJ/ YJ or CJ is only about 25" long. If you have 6" of lift or more, that DS and pinion is at a steep angle. I cant think of a reason, besides ground clearance or maintenance, that you couldnt help manage that angle better by using a DS with two CV joints. You could set your pinion angle however you want and not have driveline angle issues. The same would go for trying to manage the front driveline angles while maintaining good caster.

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Ah. Well...


You a double cardon joint (not a CV) can't travel to as great of a degree as a single cardon joint - especially one with deep yokes found in some stock applications (look at the slip yoke on a YJ). They can be ground out to recover some angle however. Also, the double cardon joints themselves are a good 5" long (IIRC), which actually makes for a shorter (and steeper) driveshaft as the first joint in the DC joint only does away with half of the operating angle. So, why would you use one? If you pinion is on the same lateral plane as your tcase output (or close enough) and you can rotate your pinion angle up to point at the tcase output - it really seems like a waste of time/money/effort, not to mention that the joints won't travel as far and will be at a greater static angle. However, say you've got a YJ with the drivetran moved back 4-6" or a doubler and you're using a diff such as the 8.8 with a laterally offset pinion - it could be helpful. Although, to me really they should just punch their wheelbase out another 6-8" and solve the bloody problem that way.


And you can change your castor in the front easily enough - got grinding wheel? Okay, I'll admit mine blows, but I only use 4wd off-road. That and my driveshafts aren't anywhere near acceptable for use above about 60km/h.

The dual cardan joints I've worked with actually have a larger angular tolerance than single u-joints. This is due to the fact that each joint only has to flex one half the angle.

The reason you would not run a standard u-joint driveline on a very lifted vehicle really has little to do with the angle each can flex to. It has to do with the change in velocity of the body of the shaft. The shaft progressively goes through two accelleration and decelleration cycles during each rotatation, and as the angle increases, this swing in velocity increases in a non-linear manner. It takes a significant amount of energy to accellerate and decellerate the mass of the system, this leads to vibrations, even if the shaft is balanced perfectly.