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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!
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| | | | Joined: Oct 2003 Posts: 5,152 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Oct 2003 Posts: 5,152 | As far as I know there is no Borg Warner OD for the SM420. I could be wrong and it wouldn't be the first time.
You can convert to something like a T-5 which will give you the overdrive, but is not a heavy duty transmission. You might find one of those for a couple hundred.
Aside from that most the transmission options are quite a bit more expensive unless you find a deal somewhere.
The 4.10 gears for the stock axle are hard to find. It may take months to find a set used.
A complete rear axle replacement might be the cheapest option. I've seen appropriate axles change hands pretty cheap. I have a Dana 70HD I was given and a GM 14-bolt that came with a $100 truck. You'll still spend money on new u-bolts and brakes, but it may not be much.
Good luck!
1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble... | | |
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