R5A51 Transmission Master Rebuild Kit Montero Sport

Master rebuild kit for the Mitsubishi R5A51 five-speed automatic, the rear-drive box behind the 3.0L 6G72 and 3.5L 6G74 V6 in the 1999-2004 Montero Sport. The same kit covers the four-wheel-drive V5A51 and the four-speed R4A51 and V4A51 units, since those transmissions share the clutch pack stackups and case sealing. Kit contents replace part numbers B124820D, B124880B and W124881B.

What is in the box: the complete friction plate set, the matching steel plate set, separator plates, and the full gasket and seal package including case, pump and valve body gaskets plus the rubber lip seals and sealing rings. That is everything consumable that comes out of the transmission during a teardown, so you are not stopping mid-rebuild to chase a single burnt clutch or a pump gasket.

These units come apart for the usual reasons. A slipping or flaring 2-3 shift means the second clutch frictions are cooked. Delayed engagement into drive or reverse after the truck sits overnight is a sealing ring and lip seal problem. Burnt fluid and clutch material in the pan means the whole set is done, not just one pack. In all three cases the correct repair is a full overhaul with new frictions, new steels and every seal replaced, which is exactly what this kit covers.

Measure the new frictions and steels against what you pull out before assembly and set clutch clearance to spec with the selective plates. Soak the frictions in ATF before they go in. New parts, sold as a complete set.