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Willys Jeep SM465 Transmission Upgrade - Granny’s Tranny

Posted in How To: Transmission Drivetrain on June 19, 2013 Comment (0)
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Old Willys Jeeps are as popular as ever these days, and old Jeep owners all have different recipes to build theirs. Lots of off-roaders are heading toward automatic transmissions, but there is something about a manual transmission that just feels right for an old Jeep, so we’re going to showcase a simple tough gearbox arrangement that is short in length but offers multiple gear options.

The Spicer 18 helped beat the WWII enemies from inside every Jeep

A classic recipe for old Jeeps has always been the super-granny-geared SM420 transmission from a GM truck with the original Spicer 18 transfer case. This is a great setup for its low gearing and short overall length, but we have found something even shorter. The SM465 is the replacement for the SM420 in GM trucks and can be adapted to the offset Spicer 18 to give you an even shorter overall gear train. Plus, by adding new over and under gears to the 18 you can still have a wide variety of gearing options. We would still like to see a short five- or six-speed transmission in a little Willys CJ someday, but this recipe offers a strong simple gearing solution that makes sense in an old Jeep.

This is the old standby when it comes to Willys Jeep transmission and transfer case combos: the GM SM420 and the Spicer 18 transfer case. This allows easy adaptation to a GM engine like a V-6 or V-8 since the transmission came behind a GM engine. The SM420 has an immense low range of 7:1 and was last offered in a GM vehicle in 1967.
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Sources

Advance Adapters
Paso Robles, CA 93446
800-350-2223
www.advanceadapters.com
TeraFlex
Murray, UT 84107
801-288-2585
www.teraflex.biz
High Angle Driveline
Paradise, CA 95969
1-530-877-2875
www.highangledriveline.com
Tri-County Gear
909-623-3373
http://www.tricountygear.com

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