Cardan joint on rear driveshaft? 71 K10

[prateroad]

Would it be ok to install rear driveshaft with a double cardan joint? I have an old school overdrive mounted to rear of my 205 and I have a double cardan joint on one end of a shorter driveshaft. Any thoughts on this?

[LS short box]

If you are thinking a double CV joint where it bolts on to the rear axle I would say no problem. My 98 Wrangler is lifted about 2-3 inches with a double CV on the rear drive shaft. 15 years no issues. I did go with 1350 u-joints.

[Richard]

Not a problem at all. Just a bit more difficult to service. Had a CV shaft made for the rear of my K10 (on the front as well). CV is at trans. 8 degree working angle at ride height and hits about 17 degrees at full droop. Note that pinion angle setup is a bit different because a CV basically is at 0 degrees. The two u-joints cancel each other out. Common practice is to set pinion down 2 degrees from driveshaft angle when CV is at trans.

[68isgreat]

Originally Posted by Richard

Common practice is to set pinion down 2 degrees from driveshaft angle when CV is at trans.

That's a great tip. I just had a rear driveshaft made for my 68 short bed K10 and my 700r4 trans/241c output shaft angle is 4 degrees, and my pinion is angled up at 7 degrees without the bed installed or a full gas tank. I have read that those two angles should be within a degree of each other, so I was thinking of putting a 2.5 degree shim in to drop the pinion down to 5 degrees. Is that not correct? When you say driveshaft angle, are you referring to the actual angle of the driveshaft installed, or the output shaft angle of the trans? I'm a bit confused, and not sure what I should be aiming for, as this is my first time building a 4x4. I have regular 1310 u-joints installed and no lift, just stock height. Any help is appreciated. Thanks!

[LS short box]

I believe I had my Wrangler CV drive shaft done Denny's drive service? I'd call them to see what they think.

[68isgreat]

Originally Posted by LS short box

I believe I had my Wrangler CV drive shaft done Denny's drive service? I'd call them to see what they think.

Thanks. I read some more and optimum working angle is three degrees, so I think I'll shim up my transmission a tad to 3 degrees, and shim my pinion down to 3 degrees so both angles are parallel.

[Richard]

Originally Posted by 68isgreat

Thanks. I read some more and optimum working angle is three degrees, so I think I'll shim up my transmission a tad to 3 degrees, and shim my pinion down to 3 degrees so both angles are parallel.

Raising the transmission will increase the working angle of the u-joint. Think you are confusing component angle with working angle. Say trans is at 4 down and drive shaft at 8 down. That is a 4 degree working angle. Raise the trans to 3 down, shaft will get steeper say 9 down. You have increased working angle to 6.

[prateroad]

Well my driveshaft won't fit tranny yoke cause it's for front output. I'll just have to shorten my original. thanks for the replies.

[68isgreat]

Originally Posted by prateroad

Well my driveshaft won't fit tranny yoke cause it's for front output. I'll just have to shorten my original. thanks for the replies.

How short will it be? After swapping in a 700r4/241c in my 68, the rear shaft is much shorter, only 37.5," not a whole lot longer than the front. Curious if yours is the same or similar.

[68isgreat]

Originally Posted by Richard

Raising the transmission will increase the working angle of the u-joint. Think you are confusing component angle with working angle. Say trans is at 4 down and drive shaft at 8 down. That is a 4 degree working angle. Raise the trans to 3 down, shaft will get steeper say 9 down. You have increased working angle to 6.

Great point. I can just leave my trans where it is at 4 down since it's tbi fuel injected, and put a 4 degree shim in the pinion to drop it down to say, 3 degrees to allow for upward wrap under load. If the working angles end up being more than 3-4 degrees (which seems possible considering my driveshaft is only 37.5"), I wonder if I should consider a double cardan slip yoke. I'll just have to find out when I finally get it on the road I guess. Hopefully this summer.