Trail Bud

That's correct. I had no handling issues.

RedneckJeep

That's the whole problem right there. It's all a compromise. You can only balance the shafts at one particular speed. When they get out of that range spinning faster than the balanced speed, they actually become out of balance. ANY little imperfection now becomes exponentially much worse because the shaft is out of it's balanced "zone". ALL driveshafts are like this. Get them out of their balance area, and strange things can happen. I said CAN happen. It doesn't always happen. Most regular car driveshafts will never see these kinda problems even when they are overspun, simply because the u-joints are not at the angles of some 4X4s. EVERYTHING counts when you are talking about 4X4 stuff. Driveshaft angle, balance, how straight the shaft is...blah blah blah. Everything makes a difference because you're kinda runnin the equipment "on the ragged edge" so to speak. Honestly, you're never gonna be able to have the best of both worlds here. Driveshafts are limited by the u-joint and how much angle it can take. The more angle, the more vibration you WILL eventually run into. I know yall are gonna think I'm an old fart when I say this...but maybe if yall are gonna go this fast, perhaps the best bet is to trailer the Jeeps. Lastly I'll say this.....I personally think the stock driveshafts are better suited for high speed than a u-joint type. Of course, they are limited in the amount of lift they can take, but man, if someone came out with that same type shaft that COULD take a high angle, that would be the ticket. Now that I've blabbed all this out.....I'll leave you with this as well......who the hell knows what happened in your case? Did yall find the direct cause? I mean it might not have been the speed you were goin, but I'm almost certain it had to be a factor. Without seein it, it's a tough call. But with what WOL has added to this thread, obviously, you're not the only one out there haulin ass in a JK with a lift. It would seem for my theory to hold water, that more people would be having the same trouble you have, so, I may be incredibly off base. Perhaps it was just a simple parts failure. We may never know. That's the bad thing about "grenade" carnage. It's cool to brag about, but it doesn't leave much in the way of evidence.

Also to address your question about balancing at higher speeds.....yes, that would help, but that gets increasingly more difficult. The faster you try to balance a shaft, the harder it becomes because of the u-joint angle. It may not be possible to balance the shaft at a fast enough speed. That's something that will have to be answered when the shaft is actually on the machine.

To PiginaJeep.....I didn't bring the "speed" thing back up to intentionally defy your request to get back on topic. I was merely answering a direct question.

Piginajeep

no problems here, i just didnt want a bitch thread starting..


A great solution is to get a hub kit, then you dont have to worry, atleast about the front anyhow.

RedneckJeep

Cool. I'm keepin it civil. Hell, I may be slap frikkin WRONG about this. I might have a chance to learn somethin....who the hell knows? I just don't think driveshafts have changed all that much, though.

Trail Bud

I appreciate your input, I'm on a hard learning curve since it already happened.
But if I can prevent it or know how to manage the problem any information on the subject is great.

Also if somebody else on the JK board can keep it from happening to them, then we all win.
That's what this board is all about.
Thanks.

RedneckJeep

Yup. That's fo sho.

Laughingstok

I need help understanding:

So lifting a Jeep obviously changes the driveshaft angle. The stock driveshaft with standard gearing (3.73 or 4.10) is designed to spin at a certain speed, sort of like a turbine on a jet. If this speed increases past a certain point, you get something like a harmonic imbalance in the metal which causes bad wobble, and could have ultimately caused the catestrophic failure?

This is similar to a turbine spinning itself apart. Am I on base here?

So knowing this, for the safety knowledge of a majority of this forum who have mostly 2.5" lifts or less and standard gearing; Is this something most of us should be worried about after getting these basic lifts?

My understanding is no, it's not a problem as the lift change and same gearing ratio will not push the stock driveshaft out of its "comfort zone."

Can anyone shed some light on this for us normal folk.

mmcan

:rotfl mao2:

The mental pic of TACKLE!!!

RedneckJeep

That's right. U-joint driveshafts are much more prone to this harmonics stuff than the type we have in the JK....what are they CV joints? If all of yall could see a driveshaft in a balancing jig, it would help greatly. As the u-joint angle increases, so does vibration. This really has nothing to do with the balance of the actual shaft, but rather the angle of the u-joint. More angle=more harmonics....however, NO angle=no u-joint cup rotation which will lead to QUICK u-joint failure. There is a point at which a u-joint will just have too much angle to properly balance out the harminic vibration. This is why I said in an earlier post that the more angle you have, the tougher it is to balance. Likewise, the faster speed you balance the driveshaft at, the tougher it is to balance. In this thread, we're seeing an instance where BOTH of those situations are being coupled TOGETHER. The Jeep has a pretty good lift, giving it a steep driveshaft angle AND the driveshaft needs to be balanced at a high speed. That's kinda narrowing your window of success a little. Without having the driveshaft on a machine to duplicate both speed and angle, there's no way for me to tell how narrow that window is......or even if there IS a window. I'm certain there must be, because if not, we'd be seeing tons of failures like this by now....I mean as many lifted Jeeps as there are with replacement U-joint driveshafts.

Trail Bud

You're right on the spinning, but from what I hear from people with many years of experience is that I must have cracked or weakened the integrity of the transfer case when playing on some rocks at some point.
I don't remember doing this directly.

They say they've NEVER seen a Transfer case come apart like mine without
having a weak point already existing. They think the case cracked (from stress of the drive line spinning and the existing crack/issue) and that caused the drive to fail due due binding up.
This sounds like it's very possible scenario.
But the drive line being out of balance and the 5:13's all contributed to the issue.

I hope this helps some what.