3 driveshafts broke in 1 week.... I'm stumped...

All this has taken place on my buddies 79 CJ5 with a 258.

Started last Friday (a week ago Friday), he got into so mud, bashed his rear-end and was beating on it pretty hard when he snapped his original rear driveshaft right in the middle...twisted it right off. Well, he is cheap so instead of buying a new one, he grabbed my old '63 4 cyl driveshaft and put that on.

We then took it for a spin, and right before a mud hole he put it from 2 hi to 4 lo, and instantly snapped the second one.

He then decided we would check the angle of the shaft, and adjusted it some, thought we felt it was no issue in the first place.

So, he took another one of my driveshafts, again off a 65 4 cyl. Took it for a ride on a dirt road, went great. decided to try 4 lo, and 100 feet from putting it in 4 lo it snapped again!

SOOO.... Here is the question: Is there a difference between the old 4cyl and 6 cyl driveshafts, and that's why he keeps snapping them, or is there something else that is wrong, and if so what could it be?

Thanks!

 

Can you confirm that the gear ratios between the front and rear differentials match?

 

Did you check the length of the driveshafts to
Ake sure they are correct? I'd be willing to bet that is part of the problem. You dont give much info as to lift, what the u joint angles are, etc so hard to diagnose what the issue is.

 

what tranfercase and what rear end? offset or centered

 

Prior to the first failure had the Jeep been operating in 4wd correctly and reliably?

 

Check the rear spring U-bolt and spring perches. If the U-bolts are loose the axle will rotate upwards (especially with the added torque from Low Range) and snap the rear U-joint. Likewise, if the spring perches have bent into an inverted U-shape.

Also, check for a broken or damaged T-case mount that may be letting things move about under there.

Either of these would commonly result in damage at the U-joint, not in the shaft wall tubing or slip splines. There's a chance you're buddy is pulling the shaft apart. As it separates, the tubes twist and then the shaft goes boom. Measure the distance from yoke-to-yoke with the rear of the vehicle jacked up and the axle dropped all the way out to ensure you have enough driveshaft length.

 

maybe some axle wrap could cause that....

 

He used the jeep all summer without any problem, and it acted fine. Wouldnt one tire just spin? it was on dirt...

They seem to be correct. the angle is straighter than the driveshaft in my 74 cj5. He has SOA with a 2 inch shackle lift.

If I remember correctly is is centered, and I believe it is a model 20 transfer case.

Yes he has used it a summer.

Makes sense, but I am surprised it only does it in 4x4. I will have him check that.

As in like it rotating sightly from torque?

 

yeah exactly....look at this video...http://www.youtube.com/watch?v=08UIvr6Sotk

 

And a very common issue with SOA. He needs some anti wrap bars.

 

Cool video.

 

axle wrap can appear on both setup...i have sua and with my 360 i do have some when i put pedal to the floor...it's maybe not his problem but it worth to take a look over it...

Just think about another thing, did you change the pignon angle because normaly in a good setup you're suppose to get the same amount of angle in the u-joint at the t-case and axle. If it's not the case you can worn out the joint and under pressure (like mudding) you could break the joint easily....

 

Because the leverage point of the axle is farther from the powersource mounting point (frame)

 

So your saying with a large SUA lift you will get the same result? Or will it be lessened by the fact normally a larger SUA lift has a higher spring rate?

 

Another reason sua doesn't have as much spring wrap is the axle is mounted directly to the main leaf which resists wrapping. When going soa you are now typically mounted to a short leaf which can move much more independently allowing more wrapping.
Any time you move the axle farther from the power source using leaf springs there can be more wrap, but the springs are usually designed to combat wrap. Usually by the design of the leaves and packs themselves and of course spring rate plays a part too. It's kind of a balancing act

 

Try putting a well built one in it and see what else breaks. That should help find the problemR)

 

two inch lift shackles with a spring over on a jeep. That could definitely cause a problem with axle wrap and twist the shaft.
I would do as suggested above and check you perches and ubolts, mounts and ditch the 2-inch shackles. the extra torque of low range, a SOA with 2inch shackles could wrap that rear up pretty good. SOA conversions cause huge axle wrap problem although it can be controlled, but with 2 inch shackles you are just asking for headaches in my opinion. If he needs the extra inches of the shackles, I would use a body lift and ditch the shackles. That may eleviate some of the problem. But, you say it used to be fine. Did he had the soa and shackles them??

 

two inch lift shackles with a spring over on a jeep.&nbsp; That could definitely cause a problem with axle wrap and twist the shaft.<br>I would do as suggested above and check you perches and ubolts, mounts&nbsp; and ditch the 2-inch shackles.&nbsp; the extra torque of low range, a SOA with 2inch shackles could wrap that rear up pretty good.&nbsp; SOA conversions cause huge axle wrap problem although it can be controlled, but with 2 inch shackles you are just asking for headaches in my opinion.&nbsp; If he needs the extra inches of the shackles, I would use a body lift and ditch the shackles. That may eleviate some of the problem. But, you say it used to be fine. Did he have the soa and shackles then??&nbsp; <br> OOPS SORRY FOR THE DOUBLE POST..