I have an 03 TJ Rubicon, and will put in a 2" Old Man Emu suspension lift and also run 1.5" engine lift (and body) to fit a high clearance skidplate. What driveline problems should I expect, what do I need to buy in advance to fix the problems, how do I fix it, and will I need to have custom driveshafts made?
Thanks for your time and help,
Andrew Whitley
Your driveshaft length will be fine with that height lift. With a 2" suspension lift, it's common that the transfer case may have to be dropped a little to eliminate vibrations... but that you're installing a 1.5" engine lift will eliminate that need. Lifting the engine at the front works the same as dropping the t-case a little to reduce the angles that can cause drivetrain vibrations. You should be perfectly fine with that combination.
Jerry
I don't have a Rubicon but there are two possible issues. The NP242 on the Rubicon has a fixed yoke rear output already so the 'usual' slip-yoke induced vibration problems on the NP241 wouldn't become an issue.
The first 'maybe' is driveshaft length. With the t-case and suspesion lifts you might over-extend it if you fully articulate the rear. I'm sure it would be fine on the road, but under full articulation on the trail it could have insufficient contact in the slip joint which might damage it under high torque (or even cause it to fall out!)
Second, it is possible that the increased angle of the u-joints with the lift could be too large for them to operate correctly. They could break if the angle is too large (again- under full articulation.) You might need a double-cardan CV shaft or a special high-angle shaft.
Do your lifts and jack up the back. See how th> I have an 03 TJ Rubicon, and will put in a 2" Old Man Emu suspension
Always plan on having vibe problems, but celebrate if you don't. Most people who lift TJs only 2" don't have driveline vibes, but there are those that do. Your addition of the motor mount lift will probably almost negate the affect of the new suspension lift as far as vibes go. Also, adjustable control arms are a very effective way to eliminate vibes.
Tim, it's not the slip yoke itself that causes vibrations, it's only the driveshaft angle that does. That the Rubicon has moved the slip yoke to the driveshaft doesn't change the lift height that will cause drivetrain vibrations. That the Rubicon has a slightly longer driveshaft due to the elimination of the t-case slip yoke will help though. :)
Jerry
-- Jerry Bransford To email, remove 'me' from my email address KC6TAY, PP-ASEL See the Geezer Jeep at
I can attest to that, Jerry. We lifted two Rubis (autos) 4.5" and both had driveline vibes before the Tom Woods CV shaft kits. It _might_ have been possible to tune out the vibes with just the control arms (I doubt it though), but the driveshaft would have been too short anyway.
Isn't the angle only an issue in two ways?
1) a u-joint has a maximum angle it can operate through2) the angle on both ends of a 2 u-joint driveshaft must be the same
Since a stock TJ doesn't have a second u-joint won't you always violate #2 except at one specific ride height (and even then whenever you flex over a bump)?
Couldn't you correct #2 by adding the second u-joint without lengthening the driveshaft provided you don't violate #1?
This is all from my mechanical eng> Tim, it's not the slip yoke itself that causes vibrations, it's only the
No, a CV (double-Cardin) joint does not allow a greater angle than a conventional joint does, that is an old wive's tale.
Jerry
-- Jerry Bransford To email, remove 'me' from my email address KC6TAY, PP-ASEL See the Geezer Jeep at
Tim, a TJ does have two u-joints on the conventional (non-CV) factory driveshaft, one at each end. But you're right, the angles on the two u-joints need to be the same on a conventional driveshaft in order for the two u-joints to accelerate and decelerate in sync with each other in order to keep things running smoothly. If you go to Tom Wood's website at
Don't discount the role of the CV joint on the driveshaft, which the Rubicon does not have in stock form.
The above was from Tom Wood's Tech Info page at
Since I am CERTAIN you will argue the point, do so with Tom Wood since he is the guy that set me straight years ago when I was mistaken about the same subject. Tom has a nifty email form you can fill in and send him the information that will prove him wrong.
Jerry
-- Jerry Bransford To email, remove 'me' from my email address KC6TAY, PP-ASEL See the Geezer Jeep at
You're right that the rear driveshaft we're talking about is not a CV driveshaft. It's only the front driveshaft on a '97 or newer Wrangler that has a CV joint.
Jerry
-- Jerry Bransford To email, remove 'me' from my email address KC6TAY, PP-ASEL See the Geezer Jeep at
Great link! Thanks!
So:
- A larger u-joint angle means a more elliptical path for the driveshaft ends of the two joints.
- This causes a greater velocity variance as the joint turns through every 180 degrees.
- The changes to velocity require acceleration/deceleration of the shaft.
- Acceleration/deceleration requires the application of force to the shaft.
- The changing forces are felt as vibration in the system.
The stock TJ *does* have a 2nd u-joint. It's just closer to the 1st u-joint than it needs to be, since the slip joint is outboard of the driveshaft instead of in the middle. This results in a shorter driveshaft and higher angles and therein lies the problem. The advantage of the CV joints is twofold. First, they allow (require) the u-joint on the other end to be aligned differently (because of the second advantage), raising the pinion and reducing the angles of the driveshaft. Second (and the reason for the first, above), they don't accelerate and decelerate the driveshaft with each revolution (since they are made of two out of phase u-joints), which is part of the cause of the vibrations in the first place. That's why they are called "constant velocity" joints.
Absolutely correct. :-) The solution to the vibration, therefore, is either to reduce the angle of the u-joints (driveshaft) or add a CV joint which will only accelerate and decelerate the coupling between the two u-joints it's built out of rather than the much greater mass of the driveshaft. (The lower (3rd) u-joint is then aligned with no angle and, therefore doesn't cause any cycling of forces.)
As does my '00 FSM, but as we're talking about rear driveshafts, Bill, you are again grasping the irrelevent. Would you believe that every TJ has a CV joint in the stock front driveshaft, and NO TJ from the factory has ever had a CV joint in the rear.
Picture of a stock rear Rubicon shaft:
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