Speedo Gear
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Drifting
Joined: Sep 2006
Posts: 1,259
Likes: 2
From: MS
If you have your original 71 M20, then the driven gear used would have been the 22-tooth Gray
(also called Silver) gear, p/n 3987922.
There were two different drive gears used on 68-70 4-speeds, but 71-up should be only one.
Best to pull the driven gear out that you have now and see what color and tooth count it is,
then you know for sure what drive gear you have.
If you need the 22-tooth, that gear is still available from your dealer for $6.83.
(also called Silver) gear, p/n 3987922.
There were two different drive gears used on 68-70 4-speeds, but 71-up should be only one.
Best to pull the driven gear out that you have now and see what color and tooth count it is,
then you know for sure what drive gear you have.
If you need the 22-tooth, that gear is still available from your dealer for $6.83.
Thread Starter
Racer
Joined: Mar 2007
Posts: 307
Likes: 2
From: Port Orange Fl
If you have your original 71 M20, then the driven gear used would have been the 22-tooth Gray
(also called Silver) gear, p/n 3987922.
There were two different drive gears used on 68-70 4-speeds, but 71-up should be only one.
Best to pull the driven gear out that you have now and see what color and tooth count it is,
then you know for sure what drive gear you have.
If you need the 22-tooth, that gear is still available from your dealer for $6.83.
(also called Silver) gear, p/n 3987922.
There were two different drive gears used on 68-70 4-speeds, but 71-up should be only one.
Best to pull the driven gear out that you have now and see what color and tooth count it is,
then you know for sure what drive gear you have.
If you need the 22-tooth, that gear is still available from your dealer for $6.83.
Thanks for the info.
Mike
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Drifting
Joined: Sep 2006
Posts: 1,259
Likes: 2
From: MS
Thread Starter
Racer
Joined: Mar 2007
Posts: 307
Likes: 2
From: Port Orange Fl
FWIW, speedo reads 10MPH to high at all speeds. Checked with GPS which is dead on in all of my other vehicles.
Thanks,
Mike
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Drifting
Joined: Sep 2006
Posts: 1,259
Likes: 2
From: MS
Yes, the rear axle ratio normally determined which drive gear would be used. Lower axles usually got the smaller drive gear with the larger driven gears, and higher axle ratios were just the opposite but there were exceptions. The 3.55 is right in the middle and could go either way so need to find out what drive gear is in there now, and your driven gear will tell you that. Going up 2 or 3 teeth should fix you up provided no other problems.
Thread Starter
Racer
Joined: Mar 2007
Posts: 307
Likes: 2
From: Port Orange Fl
Yes, the rear axle ratio normally determined which drive gear would be used. Lower axles usually got the smaller drive gear with the larger driven gears, and higher axle ratios were just the opposite but there were exceptions. The 3.55 is right in the middle and could go either way so need to find out what drive gear is in there now, and your driven gear will tell you that. Going up 2 or 3 teeth should fix you up provided no other problems.
Thanks,
Mike
