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Peugeot BA 10/5 manual (5-speed)

The weak French box of the first 4.0 Jeeps

When AMC launched the 4.0 it needed a five-speed manual on hand, and reached for a French passenger-car box: the Peugeot BA 10/5. It didn't last long. It holds the record for worst durability and the shortest production run in all of Jeep history, which is why almost everyone today replaces it with an Aisin AX-15.

A short, unhappy life

The BA 10/5 backed the 258 (4.2) and the new 4.0 straight-six between 1987 and mid-1989, in the Wrangler YJ, the Cherokee XJ and the Comanche MJ. It was a car gearbox, designed for far lower torque; behind a big six and used off-road, it was in over its head.

The structural flaw is famous: the case tends to stretch under load, and when it does the gears stop meshing as designed. Rebuilding one is usually throwing good money after bad. AMC knew it, which is why from March 1989 it began fitting the Japanese AX-15 in its place.

How to spot one and what to do with it

If you have an '87–'89 XJ or YJ with the 4.0 and a manual, it's a candidate for the BA 10/5. The French bellhousing and bolt pattern give it away —unlike anything else in the lineup. Fifth is an overdrive (0.79) and first is notably tall (3.39), which also makes it weak for the mud.

The unanimous advice is the AX-15 swap: it shares the same purpose (a five-speed behind the six) and there are well-known kits for the change. It is, in fact, the conversion the factory itself ended up making.

Specifications