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NP / NVG 231 Slip Yoke Eliminator Assembly

A highly recommended upgrade to the Jeep 231 transfer case is the Heavy Duty Slip Yoke Eliminator kit. Designed for rigorous duty Jeeps, it replaces the problematic OEM tailhousing and mainshaft with a fixed yoke design, and creates a significantly shorter New Process (or New Venture) 231 transfer case.

Jeep NP / NVG 231 Slip Yoke Eliminator
Kit, slip yoke eliminator, Jeep NP231, standard length version, YJ / TJ Wranglers
Part #: 231SYE-1
Weight: 14.90
Price: $245.99
Kit, slip yoke eliminator, Jeep NP231, standard length version, XJ Cherokee / MJ Commanche
Part #: 231SYE-2
Weight: 16.00
Price: $306.99

There are three significant problems that the 231 transfer case exhibits:

  1. Vibration: the unnecessarily long slip-yoke allows excessive u-joint angles which are the root cause of damaging vibration in lifted Jeeps, or Jeeps that have had conversion transmission upgrades.
  2. Breakage: the reduced diameter of the rear portion of the factory shaft is rife with stress risers and breakage under load is not uncommon.
  3. Driveshaft Disconnection: the slip-yoke design can slip right out the back of the transfer case at rear axle droop, disconnecting the driveshaft and allowing the transfer case to quickly lose its lubricant out the output assembly.

The 231 Slip-Yoke Eliminator solves all three of them, eliminating driveshaft vibration due to extreme angles, increasing the strength of the shaft by a few hundred foot/pounds of torque and by allowing the installation of a proper slip-style driveshaft that cannot pull out of the transfer case.

The kit comes with all items as shown in the image. Driveshafts are not included due to the myriad of different lengths and combinations available. We recommend the services of a good local or national driveshaft specialist to assist you here.

231 transfer case output shaft comparison
The factory NP231 output shaft exhibits a very weak area just behind the oil pump splines. It is not uncommon to see these shafts shear at any one of three stress risers in the section that needs most of the strength.


Jeep driveshaft vibration

The upper kit is the Ultra-Short Shaft kit that will shorten the NP231 by 7" over factory setups, for installers requiring the longest possible rear driveshaft. It's electronic speed output signal makes it ideal for 1992 and later Jeeps, or earlier Jeeps with an aftermarket electronic speedometer.

The middle kit is the Standard Short Shaft kit that will shorten the NP231 by 4" over factory setup, for installers that don't require the longest possible rear driveshaft. It's mechanical speed output signal makes it ideal for 1991 and earlier Jeeps with a mechanical speedometer.

The bottom picture illustrates a standard NP231 with factory setup and no slip yoke eliminator kit installed.

Driveshaft may be provided by your specialty national supplier or local supplier. We recommend you measure your axle yoke to transfer case yoke with the full weight of the Jeep on the wheels when ordering, for best results.