I was reading the RE 4.5" Super-flex lift kit instructions. I came across this ...

Slip yoke vibration: Caused by excessive angle on the transfer case slip yoke. Very common on vehicles with 2" or more of lift. This can sometimes be cured on 4.5" lifts with a transfer case drop kit and an RE1822 high travel slip yoke (84-95 XJ’s only since later XJ's already have the high travel slip yoke and may instead require an SYE and CV drive shaft)

I'm lifting 4.5", using degree shims and trans case drop kit. I was hoping to put off a SYE for a couple of months. Could I get a 96-01 yoke from a junk yard as a short term fix. I don't know if i have a problem, just trying to reduces the possibility of a problem. I can get a yoke cheap, and figured to put it in with the lift install.

 

Do the TC drop, shim if needed. The longer yoke wont prevent vibes, but it is good insurance against over-extending the drive shaft. If you still have vibes, start saving for the SYE.

 

That' what i figured. Thanks

 

you may already have a high angle yoke
after you do the lift jack up the back by the bumper get the tires off the ground you will be at full droop turn the DS by hand if you have any binding you will feel it and you will know you have issues to fix

 

The reason for this slip yoke is the fact that the splined section is longer, and with a 4.5 lift under full droop the rear suspention could pull the slip yoke out to the point that the rear drive shaft could fall out. I talked to Eric at RE about this a few years ago, He said that the longer slip yoke "they sell" is actuaily the same length as the one used on a stock YJ.

Using a 1" T-case drop and shims or longer shackles will "probably" take care of all your vibs up to 75 to 80 mph. Running this set-up you may not even need a SYE.

 

the length of the yoke has little to do with the angle its capable of running at

 

No kidding!! But if the drive shaft is pulled out of the t-case due to the lift, to the point that it is running at the last inch of splines it will vibe no matter what the angle, unless it is 0* angle. You need some "working angle" to make the U-Joints work properly. Lowering the t-case will make the output shaft of the t-case sit further in to the slip yoke and also reduce the driveline angle.

 

Ok, First off I know nothing about SYE setups so let me get this straight, and correct me if I'm wrong. The SYE will extend the length of the splined section coming out of the transfer case, and as a result you need a shorter drive shaft. Now this is where I'm confused. By increasing the length of the splined section coming out of the tc, you decrease the the distance between the rear end and the tc. By shortening the distance, wont that increase the driveline angles? It has to transfer the rotational force the same distance in vertical height, but in a shorter distance, which in theory means more severe vibes. Can someone enlighten me? Sorry for the hi-jack btw.

 

you kinda have the concept but there is more to it than that
if the spline part is longer it will have more spline on the shaft but it can bottom out on the bearing
the only real way to accommodate big lift and high travel is a sye

you can use bump stops and limiting straps to limit travel and keep the slip yoke but you loose travel thats OK on a trail rig but not on a crawler or xtreem 4x4

 

no the SYE
slip yoke eliminator
eliminates the slip at the TC and moves it to the drive shaft so you can have more travel and not worry about it pulling apart
its over all a better setup whatever lift you have but not necessary on lower lifts like 3" cus you till have sufficient travel on the stock setup

 

Ok, that makes more sense, having it fixed at the tc to allow further flexing, but then how does that account for the vibes caused by the drive line angle?

 

a sye has a high angle CV type joint that can handle the angle
and is setup different

look in my photos in tech there are some basic setup pics in there

 

Oh.... Now I get it! I've been trying to understand this for quite some time. So the SYE is mainly for the flex, but the CV joints are what eliminate the driveline angle vibes. Thanks

 

simply put yes
I have a CV DS and no sye it works for me cus I don't do big flex stuff

there is a pic of my CV in my pics also

 

I think I can finally do my lift. I had a buddy do a 2.5 on his 94 XJ, and had serious vibes after a few months. I only wanna do a 3" lift but heard his horror story, got scared, and with the cost of the SYE it's not an option for me. I didn't know they made CV drive shafts. Mind if I ask how much yours went for?