Rear Driveshaft Length

Hello, all! I'm looking for opinions on my rear driveshaft situation. Right now I'm gathering parts and making a plan for a NP435 swap that'll shorten my current driveshaft from about 20" from u-joint to u-joint down to about 14.5-16" depending on the transfer case I go with. Here's what I currently have:



My brain tells me that I should have a double cardan but I'm not completely convinced that I need one. Stock YJ Wrangler rear shafts are around 14.5" from the factory but use a slip yoke at the transfer case. Most of what I can find on lifting YJs and TJs are that a CV style rear shaft is a must with anything over 2.5" of lift. I'm currently around that height but I'd like to do a YJ spring swap sometime down the road with a set of 2.5" lift springs to keep the height around where I am now.

So... what say everyone? After my drivetrain is longer with the four speed, worst case I'll be around 14.5" from u-joint to u-joint for a rear driveshaft. Would you run a double cardan or no?

 

Tough call from here. I’d be inclined to keep it standard, leaving the option open to switch to a DC if you can’t shake a vibration, or if the joints max out before full droop.

Food for thought… With a DC, you’ll have the added cost of an output yoke, and the added work of cutting/turning your spring perches (or using some ridiculous shims) to get the pinion where it needs to be.

 

Does this mean with a DC joint that you no longer need to keep your transfer case main shaft and the rear pinion shaft in parallel planes? if so do you need to rotate and point your rear axle upward to point the pinion shaft more directly at the transfer case output shaft? Which would mean the rear u-joint would hardly be flexing at all, correct?

 

yes on all

 

IMHO the standard propellor shaft configuration is best if the prop shaft angle is less than a 11 degree incline.
Looks like your using a D20. So expect that you will need a double cardan joint.
My shaft angle was about 15* due to a 4 speed install.
So I had to tilt my D44 upward and add on a double cardan. I ended up with a 18” long propellor shaft.
See:http://www.earlycj5.com/xf_cj5/index.php?threads/156042/page-3#post-1797011

 

I’ve got a couple junk shafts kicking around the shop. Suppose come the day I can cut one up to cycle everything before investing in shortening my current driveshaft or a DC.