Yukon ZMBK117WS Muncie M20 7/8in 4-Spd Bearing Kit w/Synchros for 1963-1965 GM

Vehicle Fitment

• 1963-1965 GM vehicles equipped with a Muncie M20 4-speed manual transmission (cast aluminum case, 7-bolt side cover, 7/8" countershaft pin, 80mm OD input bearing)
• Common applications include Chevrolet Bel Air, Biscayne, and Impala (283/327/409ci); Chevelle, El Camino, and Malibu (283ci); Corvette (327ci); Nova/Chevy II (283/327ci); Oldsmobile Cutlass and 4-4-2 (330ci); and Pontiac Catalina, GTO, Le Mans, Tempest, and Grand Prix (326/389ci) models built with this transmission

Fitment Notes

• Confirm your transmission has an 80mm OD input bearing - a similar-looking 1963-1964 M20 kit exists for a 72mm OD input bearing and is not interchangeable with this kit
• Fits the 7/8" countershaft pin M20 case only; the later 1966-1974 Muncie M20/M21/M22 uses a 1" countershaft pin and requires a different kit

Features

• Complete bearing and synchro rebuild kit for the early Muncie M20 4-speed transmission
• Includes all new bearings required for a full rebuild
• Includes new synchronizer rings for smoother, more precise shifting
• Includes new seals and gaskets to restore proper sealing after rebuild
• Includes a small parts kit with snap rings, thrust washers, and needle bearings
• Manufactured by USA Standard Gear for Yukon Gear & Axle
• Purpose-built for the 7/8" countershaft pin, 80mm OD input bearing M20 case
• Consolidates all major wear components into a single kit for a complete rebuild in one order

Specifications

• Transmission: Muncie M20 4-speed manual
• Application years: 1963-1965
• Case type: Cast aluminum, 7-bolt side cover
• Countershaft: 7/8" pin
• Input bearing: 80mm outside diameter

Included Components

• 1x Complete bearing set
• 1x Synchronizer ring set
• 1x Seal and gasket set
• 1x Small parts kit (snap rings, thrust washers, needle bearings)

Product Description

The Yukon ZMBK117WS is a complete bearing and synchro rebuild kit for the early Muncie M20 4-speed manual transmission used in a range of GM performance cars from 1963 to 1965. It bundles all the wear-prone internal components - bearings, synchro rings, seals, gaskets, and small hardware - into a single kit, giving restorers everything needed to bring a tired or noisy early Muncie back to proper working order without hunting down parts individually.

This kit is built specifically for the earliest Muncie case design: cast aluminum construction with a 7-bolt side cover, 7/8" countershaft pin, and 80mm OD input bearing. This early M20 is easy to confuse with later-looking kits that use a different bearing size or a larger 1" countershaft pin, so verifying your transmission's exact specs before ordering is important to avoid a mismatched kit.

It's a solid fit for owners restoring an early Bel Air, Impala, Chevelle, Corvette, Nova, GTO, or similar GM muscle car with a numbers-matching or period-correct M20, as well as anyone rebuilding this transmission for a swap. Installation requires full disassembly of the transmission and is best handled by someone experienced with manual transmission rebuilds or a qualified transmission shop.