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Click on image for the lowdown. 
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| | | Forums66 Topics128,164 Posts1,056,982 Members48,458 | | Most Online14,466
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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For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Jul 2000 Posts: 2,201 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,201 | There were internal changes to the SM420 throughout the years. I replaced my 1954 SM420 with a 1967 one. The newer one has a better oil seal on the front, new syncros are available and it has a backup light switch. The Novak site has the details of the changes. https://www.novak-adapt.com/knowledge/transmissions/manual/sm420/
Last edited by Gord&Fran; 09/13/2023 2:40 AM.
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
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