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minirails

what advantage SYE's give

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A couple of weeks ago I destroyed my NP242 t-case while out wheeling. So this past weekend my friends and I hit the you pull it junkyards to try to find a replacement. My buddy Jamie got all excided about finding an NP231 with a slip yoke eliminator already added, I bought it and after trials and tribulations it is installed. My question is what if any advantage it gives besides being able to still drive without a rear driveshaft. I have several jeep friends that act like this should be standard equipment on any 4x4.

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That upgrade is on my short list. It helps with everything from vibrations to being able to flex more. If you over flex in the rear before you had the sye the driveshaft could have come out of the transfer case. Now all the movement is in the shaft itself instead of in the transfer case itself. I am sure there are other reasons but that's the big one.

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Here's what I found for a TJ:

 

The slip-yoke eliminator does exactly what it says - it eliminates the "slip-yoke". The slip-yoke is between the drive pinion gear shaft yoke and the output shaft yoke, and is designed to slip and therefore create extra length in the drive shaft when the vehicle moves up and down on it's suspension. If a Wrangler is lifted with higher springs etc, then the slip-yoke will become over-extended, and the two shafts will separate, and your engine will stop turning your wheels!.

If you are never going to get your suspension raised, then you will not need a slip-yoke eliminator kit. However, if you are going to install a lift kit, then a 2'" lift might be ok without a kit, but it is a bit of a gamble!

Some moderate lift kits come with transfer-case lowering spacers, and these mean you do not need to buy a slip-yoke eliminator kit.

The spacers are a heck of a lot cheaper than a kit!

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It is apparently true that some lift kits come with T case lowering shims. I am not sure this is a good thing, since clearance of the T case is important. If you lift it, put in a slip yoke eliminator and if it is a pretty good lift add in a CV ujoint.

 

Then you can lift the T case and some other stuff under there in a "tummy tuck" to increase ground clearance for some pretty important parts. Just my thought.

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The SYE eliminates the binding of the t-case rear output shaft slip yoke, which can be caused by heavy torque loading combined with increases in the operating angle of the rear propshaft.

 

When the slip-yoke is under sufficient torque that the splines begin to bind, preventing smooth movement, the propshaft cannot easily change lengths, as it needs to do whenever there is relative up & down motion of the rear axle, such as when going over an obstacle. When these two things happen simultaneously, there is an increased risk of the t-case output shaft being bent by the action of the propshaft trying to shorten as the rear suspension compresses ie: the axle moves upward.

 

For unmodified vehicles, unless there is high wear in the yoke this is rarely an issue, however for lifted vehicles, the angle increases, and the risk of damage also increases. In most of the instances of damage, this results in a bent output shaft and vibrations. If not repaired, the t-case output shaft will eventually fail.

 

In extreme cases, the shaft bends, then in short order it fails, and in very extreme instances, (more prevalent the higher the lift), the bending and breakage can even occur simultaneously, leaving you stranded, with a damaged and leaking t-case.

 

HTH...;)

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Awesome, Thanks for all of the good info. I never knew that the slip yoke was an issue with the 3inch lift on my jeep. I plan on more lift soon so this may come in handier than i thought.

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