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GM SM420 4 Speed Manual Transmission to the Jeep Dana 18 / 20 with 10 Spline Drive Gear, (new SM420 main shaft design) Adapter Kit

Your Price: $529.08
Retail Price:$555.53
Your Savings:$26.45(5%)
Part Number:AA-50-2402

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Advance Adapters

Our GM SM420 adapter to the Dana 18 / 20 is 4.00” in length. The adapter material is 356 T-6 heat treated aluminum alloy, and the adapter has a provision for a transmission mount. Our kit will include a adapter housing, spud shaft with 10 spline for drive gear, mount block, gaskets, seal, nylon lock nut, and adapter instructions.

Transfer case

This adapter assembly will fit the Dana Spicer 18 / 20 with a 10 tooth female drive gear. The transfer case index to the new adapter will require an index retainer & sealed bearing. Please I.D. the transfer case bore size (3-1/8”) small hole or (4”) large hole for proper retainer. Additional information can be obtained in our on-line catalog, Jeep & Scout Vehicle Section: Transfer Case Information, Jeeps 1941-79.


The kit is designed for exclusive use with the GM SM420 4 speed transmission. The SM420 was used in GM trucks 1947 to 1968 and has a 10 spline output shaft and was used in both 2wd and “divorced” 4wd applications.