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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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| | | | Joined: Jun 2023 Posts: 25 'Bolter | | 'Bolter Joined: Jun 2023 Posts: 25 | Just a curiosity, has any one ever fitted an auxillary overdrive behind an SM420 in a pickup? In Model A fords it is somewhat common for folk to fit a Mitchell overdrive behind the Ford transmission, which makes a very nice driving car, so the thought came to mind that perhaps a similar thing could be done to one of these "modern" AD trucks. Thanks! | | | | | Joined: Apr 2005 Posts: 2,097 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,097 | It was quite common to install modified Borg Warner overdrive units and others
in various torque tube vehicles in the bygone era. There is a publication from Tom Brownell
"How to restore your chevy pickup" that has some information on the system.
In my opinion the machining costs would far exceed the gain unless you had a shop with
all the tooling and welding equipment.
Fred
1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine
| | | | | Joined: Jul 2014 Posts: 892 'Bolter | | 'Bolter Joined: Jul 2014 Posts: 892 | On open drive line trucks you can fit a factory overdrive 3-speed transmission or on heavier trucks find an auxiliary transmission out of a tandem-axle truck. A spicer 5831A comes to mind. That gives you 12 forward gears, of which 10 are useful. 6231As can also be used but it's overkill. I suspect that any of these are more prevalent than an overdrive unit for a closed drive line Chevrolet. You might consider converting to an open drive line.
1951 3800 1-ton"Earning its keep from the get-go"In the DITY Gallery1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971. | | |
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