We started this NP231 buildup because we needed a slip-yoke eliminator. But after calling John at JB Conversions, we ended up with quite a bit more. First off, of course, was JB's NP231J HD Super Short SYE, our initial intention for contacting the company. Shortly thereafter, we cracked open our donor NP231 and realized that a rebuild would do it right. The chain was loose and worn, as were the gear teeth on the drive sprocket and front output shaft. JB's NP231J wide chain kit took care of these woes and will provide significantly more strength than stock.
Going deeper in the 'case, we found the stock three-pinion planetary assembly was also a bit worse for wear. Continuing the 'case strengthening parade, John suggested a six-pinion planetary assembly that would address yet another weak element of the factory design. We topped off the NP231 rebuild with a master rebuild kit, also supplied by JB Conversions.
We plan to install the SYE on an NP231 transfer case destined for use in a Jeep Liberty that will also receive a Klune-V Extreme Underdrive. We didn't need a whole lot more rear driveshaft length for the conversion, but the HD Super Short SYE kit was too cool to pass on. The kit is a full 3-1/8 inches shorter than other HD kits on the market, and it's also much stronger thanks to a variety of improvements applied to nearly every aspect of the assembly. The new 32-spline mainshaft offers a higher spline count than that of stock and is machined to exacting tolerances for continued reliability. Lubrication is also greatly improved through use of the Super Short kit, largely due to a custom tone wheel that features eight large oil passage holes instead of the four small passages in the stock part.
To carry out the complete rebuild, we acquired an NP231J master rebuild kit from JB Conversions. The kit comes with all-new components, including a front output yoke rubber seal; a front output yoke double-lip dual-spring oil seal; a front output bearing retaining ring; a front output shaft bearing; a front output shaft rear pocket bearing; a synchronizer hub retaining ring; an input-gear pilot bearing, input gear bearing, retaining ring, thrust washers, and oil seal; a shift-sector nylon retaining ring; a shift-sector shaft O-ring; a vacuum switch O-ring; a shift detent plug O-ring; an oil pump oil seal; a mainshaft rear output bearing; a rear output bearing retaining ring; a new oil pickup screen and oil-pickup tube O-ring; a new rear output housing bushing and oil seal; and new mode fork and range fork pads. It wasn't necessary for us to make any extra trips to the Jeep dealership to pick up miscellaneous small parts that aren't included with many partial rebuild kits. JB Conversions' master kit has it all.
With all of the new components on hand, we went to Rock-Tech Offroad where owner Chris Johnson carried out the installation of the rebuild parts, as well as the new Super Short SYE and the other internal beef-up parts. The end result was a beautifully prepared transfer case ready for even high-horsepower applications. You'll see more of the "NP231 Forever" transfer case in coming issues as we provide coverage of the aforementioned Jeep Liberty NP231/Klune-V conversion.