Aisin AX15 Bolt-On Transmission Swap Jeep

Transfer case: Rockland offers an HD NP231, with optional slip-yoke eliminator (SYE). To combat big-tire stress, RSG builds the HD NP231 with six-pinion planetary gearsets (compared to the OE three-pinion setup), a heavier sprocket, and a wider chain. The OE CommandTrac 27-spline slip-yoke can be upgraded by Rockland's optional 50 percent stronger 32-spline fixed yoke to eliminate oil leaks and allow more driveshaft length (about 4 1/4 inches on a YJ and 6 1/4 inches on a TJ), curing lifted-Jeep vibration in the process. Available rear yoke options are for 1310/1330 U-joints or for a CV joint. We chose the CV since this particular '88 YJ had pronounced driveline vibration resulting from 4 1/2 inches of lift.

Incidentally, RSG stresses that its direct-bolt-in HD231 is a much more affordable option than swapping in an NP241OR RockTrac (which Rockland also sells). Strength is comparable, and the RockTrac's 4:1 low-range comes at the expense of losing the speedo-the late-model electronic signal is incompatible with the earlier sending system.

Mounts: The AX15's mounting pattern is slightly different from the Peugeot's. Many "real" Jeepers can fabricate an offset plate to mate the existing mounts to the AX15. CRC Transmission chose the bolt-on route by slightly modifying an Advance Adapters plate intended for an NV3550 conversion-two notches were ground in the plate to clear trans bolts in the forward-facing side of the plate. This raises the trans about 3/4 inch and increases the driveshaft angle (another reason to choose a CV-style rear shaft and fixed rear transfer-case yoke) but keeps the overall conversion in the bolt-on realm. XJ and Commanche owners also have to modify the trans mount that mates to the exhaust flange and/or possibly swap in the later crossmember from AX15-equipped vehicles.

Driveshafts: The AX15 is the same length as the BA10, so the transfer case sits in approximately the same location. The existing front driveshaft can be retained; the RSG HD231's SYE creates additional room, so the rear shaft will either have to be lengthened or replaced if upgrading to this fixed-yoke transfer case. Once CRC had the RSG-assembled tranny/transfer case in place and the Jeep on the ground, they sent accurate measurements and the factory rear driveshaft to Coast Driveline. The custom Coast shaft combined the OE lower yoke with long-spline tube and CV upper joint. Vibration cured!

This job is straight-up R&R-no adapters or cut-n-paste fakery. Jeepers who can change their own clutches can likely handle the task. To avoid our having to wield a wrench in one hand and a camera in the other, CRC Performance Transmissions agreed to handle the in-and-out, which is easier with a professional transmission jack. During the job, CRC owner Craig Calkins shared these tips from his 25-plus years of working on 4x4 geartrains. (See the photos and captions for other observations.)
* Never grease the clutch/trans input-shaft splines.
* Deburr the trans housing where it mates to the bellhousing if necessary.
* If replacing the pilot bushing, always use the proper puller; don't lube a sealed-brass replacement; lightly lube a new bearing type pilot.
* Resurface or replace the flywheel as necessary. (Remanufactured flywheels are often cheaper than having the existing one resurfaced.) If the flywheel checks out (no high spots or hot spots), hand-sand the clutch surface with a sanding block to break the glaze.
* Replace the clutch assembly and release bearing in conjunction with the trans swap.
* Tighten pressure-plate bolts by hand. Uneven fingers means that something's wrong.
* Index the speedo gear correctly when transplanting it from the BA10 to AX15 to ensure the correct ratio.
* Shim the transfer-case linkage as necessary with washers to make it fit flush on AX15 housing.
* Use Loctite on skidplate bolts to discourage overtorquing and stripping out frame nuts.
Overall, this swap is an efficient solution to the Peugeot problem. Rockland took the guesswork out of the spline/gear and pilot-bushing variables, and CRC dialed in the details to demonstrate how a trans conversion can be executed to look OE with no fabrication or special mechanical skills required. The bottom line here is that Peugeot gears are great for 10-speed bikes, but they have no business in Jeeps.