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Mod | | | Forums66 Topics128,183 Posts1,057,263 Members48,467 | | 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!
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| | | | Joined: Jan 2007 Posts: 199 Shop Shark | | Shop Shark Joined: Jan 2007 Posts: 199 | My 59 SM420 transmission is missing the speedo drive gear and Carter has some. I know the axle ratio but how do I determine the number of teeth on the speedo drive? They say they need that info to matchup to the bucket of used ones. Its 3:90 diff. | | | | | Joined: Sep 2007 Posts: 2,644 Shop Shark | | Shop Shark Joined: Sep 2007 Posts: 2,644 | Let's see... a 4:56 is 13 teeth, a 4:11 is 12 so I guess it would be a safe bet that you need an 11-tooth gear... but that's only a guess based on what I know.
Now that I've gone on record I'm sure someone will be by shortly to correct me. | | | | | Joined: Jan 2007 Posts: 199 Shop Shark | | Shop Shark Joined: Jan 2007 Posts: 199 | Thanks Woody. I actually started thinkin about my diff and realized I was not at 3:90. That is my old MGB rear axle. Too many projects! So I went out and jacked up a wheel on the 59 and counted. It is really the 4:11. So if 12 teeth for the speedo gear is correct for a 4:11 I can order one from Carter now. Appreciate the jogging of my cluttered project memory. Ralph | | | | | Joined: Oct 2006 Posts: 9,671 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 9,671 | Hey Rasman, what does JC want for the gear??
Denny Graham
Sandwich, IL
Denny G
Sandwich, IL
| | | | | Joined: Jan 2007 Posts: 199 Shop Shark | | Shop Shark Joined: Jan 2007 Posts: 199 | Denny & Woody,
They are gonna call me back if they have any for a 4 speed. Around 30-40 bucks. They told me they do NOT have any for a 3 speed for certain. Ralph | | |
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