JR405E Transmission Master Rebuild Kit, Mazda RX-8

This is a master overhaul kit for the Jatco JR405E four-speed automatic, also cataloged as the Mazda RC4A-EL. It covers the whole teardown in one box: the complete gasket and seal set, the friction plate set, the steel plate set, the O-rings and the metal-clad seals you have to replace once the case is split. Buying it as a kit keeps you from stopping a rebuild halfway because one lip seal was not in the reseal bag.

The JR405E / RC4A-EL is the rear-wheel-drive Jatco four-speed used behind the 1.3L Renesis in the 2004-2005 Mazda RX-8 automatic, and in the 1.8L and 2.0L Mazda Bongo of the same years. The same family is used in Isuzu D-Max and Trooper diesel applications. It is a longitudinal unit with an overdrive and a lockup converter, and the parts that put it on the bench are almost always worn frictions and hardened seals rather than a broken hard part.

The failures that lead here: a slipping or flaring 2-3 shift, a delayed engagement into drive when cold that clears up after a few minutes, converter shudder at light throttle, or fluid that comes out dark with friction material suspended in it. All of those are friction and seal wear, which is exactly what this kit replaces. Once the unit is apart, replace every rubber and friction item in the box rather than reusing anything that still looks serviceable - the old seals have already taken a heat set and will not seal against a freshly honed bore.

On the bench, soak the new friction plates in clean ATF for at least 20 minutes before assembly, check each clutch pack clearance dry against the factory spec with a dial indicator before you button it up, and replace the filter and flush the cooler and lines before the rebuilt unit goes back in. Debris left in the cooler circuit will come straight back through the new frictions.