4x4jeepmanthing

a shop had the jeep on a lift, while doing so they noticed the front drive shaft is pretty much maxed out on compression at full droop. This could be bad for the TC if some crazy articulation happened.

so, if it can be done do i have a shop increase compression length, or buy a new shaft, and would new have the same issue?

99 auto np242 RE 3.5" 33s

andrewmp6

Limiting straps work in that case.

XJlimitedx99

New driveshafts would be ideal. It doesn't really make sense to spend money on lengthening stock shafts. With that being said, I do not think you need that. I've been wheeling with 6" lift, long arms and a stock front shaft for a couple years and have never extended my driveshaft to the point of it pulling apart. I'm sure it would if I had different steering and longer shocks and brake lines but that's beside the point.

Why do you say it would be bad for the transfer case? If anything I would think it would over extend to the point that there is very little spline engagement left and twist the splines. I say run it. If it breaks then you'll know you need new shafts.

4x4jeepmanthing

its bad because if you were to collapse/compress the Dshaft violently enough ---><----=blown out TC. the TC is aluminum and will likely give before a DS. the UCA/LCA are not adjustable so i am unable to stretch the axle forward. This is an if scenario, but the damage would be rather bad if this was to happen.

XJlimitedx99

I'm confused on how this shop said the driveshaft is bottoming out on compression from having it on the lift. I originally just thought you were talking about extending and just using the wrong terminology. With a stock driveshaft and bump stops there is no way for the suspension to travel up far enough to bottom out the driveshaft.

TRCM

On a front driveshaft, the driveshaft compresses as the axle moves down and back (droop) because it gets closer to the t-case......this is more noticeable on a high pinon fornt axle

The farther down the axle moves, the more rearward the control arms pull it, which compresses the shaft.

BUT, to see this they had to have the axle hanging while on the lift arms.


Remember, a rear axle moves up and back on compression (flattens out the rear spring), which pulls the splined joint apart due to the axle moving farther away fro the tcase.

But on a front axle, especially a high pinion one, droop will compress the driveshaft.

Ignoring the driveshaft u-joint angle, the front axle is the farthest away from the tcase (max extension of the driveshaft) when the control arms are perfectly level. Anything else will pull it closer to the tcase because of the arc the control arms move in, and droop (suspension extension) will do so more than suspension compression due to the relationship between the axle & the control arms that give you caster. As you compress the suspension, the pinon is actually rotated up, and this effectively lengthens the driveshaft while giving you a crappy u-joint angle.

On a high pinion axle, the pinion is already above the centerline of the axle so as it rotates up during compression of the suspension, it starts to extend the driveshaft right away.

On a low pinion axle, the pinion is below the centerline of the axle, so as it rotates up, it will compress the driveshaft slightly until the pinion crosses the centerline of the axle, at which point it will start to also extend the driveshaft.


Ever notice when you put a lift on, the front tires move back in the wheel well opening ? That is because the angle of the control arms is such that the distance from the tcase to the pinion is now shorter, and the driveshaft more compressed.


When I put my control arm drop brackets on, it moved my axle back to centered in the wheel well and leveled my control arms out....it also extended my front driveshaft back to normal.



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4x4jeepmanthing

This is great Info that I've never come across! Good for prospective builders

XJlimitedx99

I SEE, said the blind man. I was under the impression the down travel moved the pinion away from the case at a rate greater than the backwards travel was moving it closer.

Thanks for explaining that.

investinwaffles

A new custom HD shaft will be close to $300.

​​​​​​I had a stock WJ shaft lengthened and balanced for $70 for my rear SYE install which was within my budget.

Atmos

where are you located? Limit straps are ideal, or you can post up in your local forum section and ask for someone to chop the CV off, shorten the shaft, and weld the CV back on. if the driveshaft is already removed from the jeep it's about 30min worth of work someone will probably do it for beer and pizza. I know I would, I'm located in the Sacto CA area

TRCM

can't move the axle farther away unless the control arm gets longer.....but the location of the pinon in relation to the tcase does change since the control arms basically keep the axle in the same position with respect to the steering axis inclination angle (angle if you drew a line between the upper & lower balljoints) and the body/chassis, just like any 3 or 4 link does


long arms or radius arms don't hold the steering axis inclination angle the same in relation tot he body/chassis as they cycle up & down, they hold it the same in relation to the control arm itself.



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4x4jeepmanthing

im in CO.

I know the new shaft would be $$$ money i dont want to put towards a new front shaft. I have to call some shops. Where did you go Waffles?

Atmos, Ive looked at straps, but all the dudes running these have them welded to frame stiffeners. I cant weld so im not sure whats cheaper lol, mod the shaft, pay for someone to weld straps,LA upgrade(ok not cheap) or buy new.
just dumped a lot of coin into the jeep so this isnt something im going crazy over, but when i do address this i dont want to cheat drive train reliability.

The shop that told me of this only mentioned it as something to be aware of as an extreme circumstance issue. ide have to do something just right for this to really go bad, but it is still a possible issue until I choose: DS, adjustable LCA/UCA's, or straps. The chance that I have the suspension that drooped offroad is unlikely. If ide known about this issue before choosing a lift, I would have made a different decision on control arms, or some other option to eliminate the issue, but i know now and i dont like it haha. Again likely not going to be a problem, but if it was to happen, and the TC bites it in the rockies, shes dead in the water far from a tow.

are straps something that you can add to the frame and axle without welded on brackets, not sure ide trust thin frame metal + an axle pulling the vehicle weight around.

thanks for all the ideas you guys have had!

investinwaffles

I went to Colorado Drive Shaft, really close to 76 and 25

https://goo.gl/maps/sK1Y1Gxovtw

You can check Bill's Englewood driveshaft too, but they are more expensive. Rocky Mountain Driveline is up in the Highlands off Tennyson and 38th but I have never used them

Just tell him to make sure the weights are welded on tough, I ripped one off like the first time it touched a rock. Welds look much better now

Honestly, that shaft is just too short - control arms aren't going to make any difference. Just get it lengthened, shouldnt cost that much - limiting straps are really not going to be that much cheaper...