Muncie 4-Speed Rebuild Bearing Kit M20 M21 M22 1966-74

This is the bearing and synchronizer rebuild kit for the later GM Muncie 4-speed, the version built with the larger 1-inch countershaft pin. Before you order, confirm your case: a cast aluminum housing, a 7-bolt side cover, the 1-inch countershaft pin, and an 80mm outside-diameter input bearing. That combination is the BK116WS group and covers the M20 wide-ratio, M21 close-ratio, and M22 rock-crusher boxes from roughly 1966 to 1974.

Inside you get every wear item that spins or seals: the input, output, and countershaft bearings, the full set of brass synchro rings, the front and rear seals, the side-cover and bearing-retainer gaskets, and a USA-made small-parts kit with the snap rings, thrust washers, and needle bearings. The bearings are Japanese Nachi and Koyo, not no-name stampings, so the box turns quiet and stays that way.

This is a soft-parts and bearing kit, not a hard-parts kit. It does not include gears, shafts, forks, or the case, so reuse those if they measure in spec or source them separately. If your gears and shafts are good and you are chasing bearing whine, worn synchros, or a leaking seal, this is the kit that puts the box back together.

Rebuild it on the bench with the side cover off: press out the old bearings, swap the synchro rings while the gear stack is apart, set your endplay, and reseal. Pair it with a Muncie rebuild manual if this is your first one.