NP231 Slip Yoke Eliminator Kit 32-Spline with 1310 Yoke

This is a slip yoke eliminator (SYE) kit for the New Process / New Venture NP231 transfer case, the chain-drive unit used behind the AX5, AX15, AW4 and 32RH in the 1987-2006 Jeep Wrangler YJ and TJ, the 1984-2001 Cherokee XJ and the 1993-1998 Grand Cherokee ZJ. It replaces the factory slip-yoke rear output with a fixed 32-spline mainshaft, a short tailhousing and a 1310-series CV yoke. Interchanges with Crown RT24005, Rugged Ridge 18676.60, Mopar 52231, Rough Country 50-7906 and 4444401.

The problem it fixes is the stock rear output design. On a factory NP231 the rear driveshaft slides in and out on a splined slip yoke that rides inside the tailhousing, so the driveshaft has to be long. Lift the Jeep and the pinion angle steepens, the u-joints run past their working angle, and you get a driveline vibration between 45 and 65 mph that no amount of shims or transfer case drop will fully cure. Break a rear shaft and the yoke pulls out and dumps the transfer case fluid on the road. The SYE shortens the output by roughly 4 inches and moves the slip joint into the driveshaft itself, so you can run a shorter double-cardan shaft, rotate the pinion up to point at the transfer case, and kill the vibration.

Installation is a bench job on the transfer case. Drop the case, split the halves, pull the oil pump and the factory mainshaft, then install the new 32-spline shaft with the supplied speedometer/tone ring spacers, reassemble the case halves with fresh RTV, and bolt the short output housing and seal on the back. Torque the 1310 CV yoke nut down against the shaft shoulder and refill with the correct ATF for the case. Plan on a new rear driveshaft with a double-cardan joint at the transfer case end - this kit does not include one. Adjustable control arms or a shim to set pinion angle finish the job.