Are these a must?

[DarkWolfTJ]

I just bought a RE 3.5" super flex kit ( with the 4.5" kit parts), I keep hearing though that I should also get a slip yoke eliminator and/or a CV Drive Shaft. My questions are first off what are they, do i need both together, and do i need them at all?

[Desertracer]

A slip yoke eliminator changes the rear output on your transfer case. A slip yoke, which is what you have now, means the rear driveline slides into the transfer case on a shaft with splines on it. When you lift a vehicle, the angle of the driveline changes and causes the driveline to vibrate. A slip yoke eliminator changes the output to one in which the driveline bolts on. You then have to get a CV type driveline to mate up to that new flange. CV style drivelines are able to operate at tighter angles, thus eliminating driveline vibrations. Does that make sense? I don't know if you need one for your TJ...I would think you do.

[Materdaddy]

Usually with any lift over 2" (and sometimes only a 2" lift with a D44) you will experience driveline vibrations. Most people just lower their transfer case skid to eliminate vibrations. This can be done like this:
http://www.4x4xplor.com/t-casedrop.html

There's a slightly more expensive way to eliminate these, which is by doing a motor mount lift. This raises the front of the drivetrain in such a way that the rear output shaft is lowered, lessening the angle of the driveshaft. You'll probably need to do a body lift to accomidate the engine height change for this. Can probably be done for $150.

The most preferred method is the SYE/CV Driveshaft combo. Desertracer explained it well, if you still have questions, let us know! Here's how to do the SYE/CV driveshaft yourself:
http://www.4x4xplor.com/SYE-CV.html

[Mtbikbob]

Just had mine done........and if you dont do the work yourself....it ain't cheap. As you can see in my avatar, this is the way it looked before the change over.

Bob

[YJwonderboy]

is it necessarily a BAD thing to keep the stock driveline? It causes vibrations...what do those lead to?

[Black & Tan TJ]

I went through the same thing a few years back. I got the same lift but it seems like some stuff was left out or just vague. I ended up with the SYE & shaft (just $500 more + istall) and also needed the angle bracket for the rear diff. the kit come with a straight bracket. Most everyone get the vibs and you can't drive like that for long, it will wear out bearing, bushings & seals prematurely ending up costing more in the long run. Just do it right.

I'll bet if they added up all the stuff you need after the lift is installed we'd think twice about it, those hidden cost always get you.

Just do it right the first time or not at all, B&T TJ

[DarkWolfTJ]

so what is it exactly that i need to get, im still a little confused... a sye and cv?

[blkTJ]

so what is it exactly that i need to get, im still a little confused... a sye and cv?

yup, and upper OR lower adjustable rear control arms.

[Materdaddy]

is it necessarily a BAD thing to keep the stock driveline? It causes vibrations...what do those lead to?

Usually leaky pinion seals.

[MLA 97TJ]

I installed the same lift kit on my Jeep. We went for a test drive when it was finished and it vibrated pretty bad. We had the SYE kit and new driveshaft installed and the control arms adjusted correctly. Now it drives great with no vibrations.

[maddmike]

you will need an SYE with this amount of lift. with the rear of my vehicle completely unloaded I get very slight vibrations around 25mph and i have the transfer case drop kit installed and no SYE on a 2.5" lift. even with a motor mount lift and transfer case drop, i'm not sure you're going to eliminate the problem.

if you don't have the cash for this stuff, i'd recommend returning or selling the parts and going with a 2-2.5" lift, which is all you'll need anyway to do about 90% of the wheeling in the USA. you just won't look as cool as all the guys with 35" tires.