Longer Single Cardan Driveshaft vs New Double Cardan Driveshaft

Don Bulee

Don Bulee

TJ Enthusiast
Joined
Apr 13, 2021
Messages
306
Location
Mex
Hello,

Two months ago I installed a 4.5 inch lift from Rubicon Express (I also have a 1.25in BL) in my Rubicon 06, the SYE was not needed because its a Rubi, but regarding the driveshaft..... my neighbor have a shop and he usually makes the driveshafts (or repair them) for big trucks, semis and all that kind of big boys... he told me that the DC driveshaft wont be needed but the lenght of my driveshaft needs to be improved (enlarge it a bit) he told me that if I want he can charge me like 75 bucks (he is being nice) for making my driveshaft a few inches longer because of the lift added to my TJ (he knows how to, not sure if welding cutting and all that stuff).... I barely have some vibrations at 5/10 miles per hour.. like really really small vibrations (can live with them forever haha) and after 12 mph the vibrations are gone and no other issues with the driveshaft (the adjustable upper rear control arms made the trick), so here comes the question... Do the DC driveshaft is needed or I can save myself a few hundreds by accepting the favor and just enlarge my current driveshaft a few inches to compensate the lift added... thank you!

Ps. Tbh, I'm more concerned in having a broken driveshaft because being too short than the vibrations, as said... the vibrations are like barely present
and I still haven't added the MML (maybe the next month)

20220606_160647.jpg
 
not sure why I can upload more

20220606_160625 new.jpg


20220401_125707 new.jpg
pictures in the original post, but here are two other pictures to help in my post..
 
jjvw said:
I didn't read the rest. You need a DC rear drive shaft. And upper and lower adjustable arms.
Click to expand...

Since I barely have a few vibrations what would be the reason or what would be the difference of the DC instead of just having my SC enlarged? thanks!
 
Don Bulee said:
Since I barely have a few vibrations what would be the reason or what would be the difference of the DC instead of just having my SC enlarged? thanks!
Click to expand...

Because you have vibrations, even if they are barely. You don't want any vibrations. Droop the axle and the vibes only get worse.

Lengthening the existing shaft does nothing to soften the angles of the u joints.
 
jjvw said:
Because you have vibrations, even if they are barely. You don't want any vibrations. Droop the axle and the vibes only get worse.

Lengthening the existing shaft does nothing to soften the angles of the u joints.
Click to expand...

That make sense... 🤔...
 
Without a DC driveshaft, your rear pinion is supposed to
Don Bulee said:
Do the DC driveshaft is needed or I can save myself a few hundreds by accepting the favor and just enlarge my current driveshaft a few inches to compensate the lift added... thank you!

Ps. Tbh, I'm more concerned in having a broken driveshaft because being too short than the vibrations, as said... the vibrations are like barely present
and I still haven't added the MML (maybe the next month)
Click to expand...
Do what you want if you can live with the vibes.
Most lifts don't require a longer driveshaft.
Check it at full droop. The angle at the transfer case might be a bigger problem than the length.
Also, a bigger reason to get a DC DS.
 
Nobody notice his current setup is completely wrong for a single cardan driveshaft?

With a single cardan, the operating angle on each u joint should be equal, your current setup looks like it has a near 0* operating angle at the axle side u joint.

That is why you have some vibrations now, and any amount of vibration is too much and will eventually cause a failure of the driveshaft or possibly other parts.

For your current setup, you need to rotate the pinion angle down towards the ground until the angle of the face of the yoke on the axle is the same as the angle of the face of the flange on the transfer case.

If you do this, your vibrations are likely to get worse, not because it's the incorrect way to run it, but because you are exceeding the maximum operating angle of a single cardan shaft.

The only correct fix is to get a double cardan shaft and adjust the pinion angle accordingly. Doing so will also allow you to get rid of what looks like a skid plate drop in one of your other pictures, which will get you a little bit more clearance there and also give you the ability to do a tummy tuck later on in the future if you wish to do so.

Just fix it correctly and be done with it. Catastrophic driveshaft failure isn't anything to laugh at
 
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Double cardan driveshaft and adjustable control arms.

Don't half ass things ;)
 
Funny, the lift kit probably rotates the pinion up assuming you put in a DC. You don't need adjustable arms unless the DC doesn't fix it. Like @Trevlaw said, the pinion looks close to the right angle for a DC.
 
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