Rear Driveshaft Slip-Yoke Eliminator (SYE)
Update: September 5, 2005
I have had the RE rear driveshaft off my Jeep for a month now. Amazingly, almost all of the vibrations that I have been enduring since the regear to 4.56 disappeared immediately so it looks like the RE shaft has caused me yet another headache. All I can figure is that the regear caused me to have to drive at a higher RPM for the same speeds, and that difference made the imbalance more noticeable. I'm driving around in Front-Wheel Drive until I can install a new SYE and rear driveshaft; the worst part of this is that because of budget and time problems, I have never taken the RE shaft four-wheeling so it hasn't been bent. It's just out-of-balance from the manufacturer. Coupled with the other driveshaft issues I've had from the RE kit, I really can't recommend the Hack-n-Tap and RE driveshaft in the future.
Late model 96+ Cherokee driveshaft. note the rubber boot around the slipyoke.
There are two main versions of the NP231 transfer case as used in Jeeps.
The benefit of the Hack-n-Tap is that the installer doesn't have to open the transfer case; and in most cases the entire installation can be done in the driveway without removing the t-case at all! The downside is that some acclaimed driveshaft makers including Tom Woods will not build a driveshaft for a Hack-n-Tap equipped vehicle because of the possibilities of having imbalanced flanges or off-center cuts on the driveshaft. While there is an option to build your own driveshaft orfind the parts to make it, I'm not going to touch on that any farther.
Most SYEs for the NP231 involve opening the t-case and replacing the mainshaft with another. Either this is a completely new mainshaft that is harder than the stock one, or it is a stock one that has been cut and machined - you can usually identify this type because they require your old (usable) shaft back again. If you have any question about it though, ask the dealer or drop me a line and I'll see what I know about that kit.
The SYE I selected for Round II is of the latter type. I need to remove the stock mainshaft and replace it with a stronger unit. For this, I selected the Performance Offroad Center (PORC) NP231 SYE, and will document that installation here.