Yukon Gear 66-74 Muncie M/T w/SynchroS Bearing Kit

Complete Bearing and Synchronizer Kit for Muncie M20, M21, and M22 4-Speed Transmissions

The Yukon Gear YUKZMMK116WS is a complete bearing kit with synchronizer rings engineered for the Muncie M20, M21, and M22 4-speed manual transmissions used in 1966-1974 GM muscle cars. This kit provides every bearing, race, and synchronizer ring needed to properly rebuild or freshen a Muncie 4-speed from a single part number, eliminating the time-consuming process of sourcing components individually. All bearings in YUKZMMK116WS meet or exceed OEM specifications for load rating and dimensional accuracy, and the synchronizer rings are manufactured to the correct friction material specification to restore crisp, precise shift feel.

Key Features

• Complete kit for Muncie M20, M21, and M22 4-speed transmissions with synchronized gears
• OEM-grade bearings with correct load ratings and dimensional tolerances
• Friction-material synchronizer rings restore precise, smooth shift feel
• All components sourced from one part number, no multi-supplier sourcing required
• Backed by a Lifetime Limited Warranty under the Magnuson-Moss Warranty Act

Specifications

Fitment

What's Included

• Input shaft bearing
• Countershaft (cluster gear) bearings
• Output shaft pilot bearing
• All synchronizer rings
• Snap rings and small parts

Frequently Asked Questions

Does this kit cover the M22 Rock Crusher as well as the M20 and M21?
Yes. YUKZMMK116WS is correct for all three Muncie variants produced from 1966 through 1974. The bearing and synchronizer specifications are shared across these variants in this production period.

What is the difference between this kit and the YUKZMBK117WS?
The YUKZMBK117WS is the correct kit for the earlier 1963-1965 Muncie M20 and M21 transmissions, which use different bearing and synchronizer dimensions. This kit covers the 1966-1974 production run, which includes the M22.

How do I identify whether my Muncie needs this kit or a different one?
Identify your Muncie by the date code stamped on the case. Codes from 1966 onward indicate this kit applies. Also verify whether your transmission has synchros on all forward gears, which is required for this kit.

What is the warranty on this bearing kit?
Yukon Gear backs this kit with a Lifetime Limited Warranty. As a drivetrain component, it qualifies for consumer rights under the Magnuson-Moss Warranty Act.

Do I need to replace the synchronizer rings even if mine look okay?
Yes, when performing a full rebuild. Synchronizer rings have a wear pattern matched to the used brass cones on the gears, and mixing worn rings with new bearings accelerates wear. Always replace rings during a complete rebuild.

Can I use this kit for a Muncie in a Pontiac Firebird or GTO?
Yes. Pontiac muscle cars used the GM Muncie 4-speed, and the same bearing and synchronizer components apply. Verify your transmission code to confirm the Muncie is present rather than a different 4-speed variant.

Is special tooling required for the Muncie rebuild?
Yes. Snap ring pliers, a bearing press, a transmission jack, and a shift fork alignment tool are required. Refer to the Muncie factory service manual or a dedicated Muncie rebuild guide for the full procedure.

What lubricant should be used after rebuilding with this kit?
The Muncie 4-speed uses GM Synchromesh or equivalent MT-90 gear oil. Do not use standard gear oil or limited-slip additives, as they will damage the brass synchronizer rings.

Installation Notes

• Verify transmission date code and variant before ordering to confirm applicability
• Use a press for all bearing installations; do not drive bearings in with a hammer
• Inspect shift forks, detent balls, and the case for cracks or wear while the transmission is disassembled
• Replace all snap rings with new ones from the kit; do not reuse old snap rings
• Refill with GM Synchromesh or MT-90 equivalent fluid to the specified capacity

California Prop 65 Warning

WARNING: This product can expose you to chemicals including lead and lead compounds, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov.