Wrangler Tranny Swap
By Grant Pearson

When the Wrangler first hit the showroom in '87 to the death of the 4.2L six in '90, Jeep used a Peugeot 5-speed as standard equipment with the 258. If you own a Wrangler with one of these transmissions, you likely know how weak they are and how grossly expensive they are to rebuild/replace. Here's an alternative to shelling out the dough on another Peugeot transmission that won't last any longer than the first. With the entrance of the 4.0L engine into the Wrangler also came a new 5 speed, the Aisin AX-15. This transmission is easily capable of handling the extra horsepower the 4.0L produces and can take all but the most abusive small block V8 without complaining. While the internals of these two transmissions vary greatly in strength, externally they are very similar. Both transmissions are 24.25" in length including bellhousing and transfer case adapter. Both use a 1 1/8"-10 spline input shaft with a .590" pilot tip diameter. They also have the same bellhousing and transfer case mounting patterns. This means you can use the same clutch assembly and not worry about relocating the transfer case and the subsequent driveshaft modifications. Sounding like an easy swap? There's just one catch. The Peugeot transmission uses a 21 spline output shaft while the Aisin uses a stronger 23 spline output. In order to use the AX-15, you'll have to replace the input gear of your NP231 transfer case to a 23 spline (the old 21 spline gear makes a great paperweight). The Jeep part number for the 23 spline input shaft is 5300-6085. If your dealer doesn't stock it, Advance Adapters has it under part number 716053. The transfer case will have to be completely disassembled to install the new gear and you may wish to have a transmission shop do the work if you're not comfortable with replacing it. Now would be a good time to consider replacing or upgrading your clutch if need be. You can reuse the old clutch disc, pressure plate, and pilot bearing if they are in good shape, but you will have to replace the throwout bearing and slave cylinder assembly with an AX-15 unit. I would strongly suggest purchasing the AX-15 from a salvage yard as you will need several small brackets that could cost you a fortune at the dealer. These brackets are generally left on the transmission when it is sold at the salvage yard. Make sure the following parts are still on the transmission when you buy it: bellhousing, transmission mount, transfer case shift linkage, and transmission shifter. This transmission swap won't leave you with an ultra low "granny" gear and a huge cast iron case capable of duty in a one ton truck. What it does do is give you a very reliable 5 speed for far less than the cost of a rebuilt Peugeot.

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