Speedometer Whoa's.......
Thread Starter
Instructor
Joined: Dec 2002
Posts: 174
Likes: 1
From: brandon florida
Speedometer Whoa's.......
The speedometer on my 72 is about 15 mph off!
Now the rest of the story, i recently installed a Richmond 3.70 gear and am aware that the speedo cable gear must also be replaced but i'm not sure where to start! Call the local Chevy dealer and they were clueless! Is there a formula or known conversion where the speedo gear teeth added or subrtracted equals so many mph increase or decrease? If so, which is it, add teeth = mph gain or subtract teeth = mph gain? Someone please help!!!!!!!
Now the rest of the story, i recently installed a Richmond 3.70 gear and am aware that the speedo cable gear must also be replaced but i'm not sure where to start! Call the local Chevy dealer and they were clueless! Is there a formula or known conversion where the speedo gear teeth added or subrtracted equals so many mph increase or decrease? If so, which is it, add teeth = mph gain or subtract teeth = mph gain? Someone please help!!!!!!!
Heel & Toe
Joined: Jun 2007
Posts: 15
Likes: 0
Speedo Off
There's a guy up in Flint Michigan that may be able to help you, I will look up my history on my browser to see if I can get you his number. You can only change the external gear so much. If that doesn't get close enough he builds a small gear box that goes inline for the fix. Try www.specmo.com
Regards, Neal
Regards, Neal
Last edited by nealkeith; Jun 25, 2007 at 08:17 PM. Reason: add info
Thread Starter
Instructor
Joined: Dec 2002
Posts: 174
Likes: 1
From: brandon florida
Safety Car
Joined: Oct 2004
Posts: 3,927
Likes: 740
From: Youngstown Ohio
http://www.tciauto.com/Products/Tech...eedo_gears.asp
Instructor
Joined: May 2006
Posts: 221
Likes: 1
From: Albuquerque New Mexico
Note: If your speedometer reads too high, a driven gear with one more tooth will slow it down approximately 5 MPH. This is from Corvette Central and it works for the factory four speeds, My book says a 42 tooth gear for a 3.70 with a automatic factory trans. What gear how many teeth are you running now?
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Safety Car
Joined: Oct 2004
Posts: 3,927
Likes: 740
From: Youngstown Ohio
Note: If your speedometer reads too high, a driven gear with one more tooth will slow it down approximately 5 MPH. This is from Corvette Central and it works for the factory four speeds, My book says a 42 tooth gear for a 3.70 with a automatic factory trans. What gear how many teeth are you running now?
Your numbers look good......I'm running a 45 tooth with my 4.11 auto and used a 43 tooth when I had 3.90's......this is with the factory 15 tooth drive gear in the tranny.
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
I am trying to find the right gear for a my 4 speed in my '75. I have the 3.70 rear end, but the prior owner never changed the gear. The document above references a 22 tooth gear for the '72, but it appears that a 20 tooth gear is specified for the '73 & '74. Do you know which is used for the '75?
Thanks for an assistance you can provide.
Instructor
Joined: Aug 2006
Posts: 134
Likes: 0
From: Apple Valley MN
Note: If your speedometer reads too high, a driven gear with one more tooth will slow it down approximately 5 MPH. This is from Corvette Central and it works for the factory four speeds, My book says a 42 tooth gear for a 3.70 with a automatic factory trans. What gear how many teeth are you running now?
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
I pulled the speedo cable off the 4 speed and the color the gear was blue, as indicated in your chart. However, I passed an automatic radar station and I my indicated speed was about 7-8 MPH over the radar. The previous owner told me it was changed to a 3.70, but I have confirmed yet.
Can anyone give me a recommendation for a gear that will offestt this 7-8 MPH overage I am experiencing.
Thanks for the assistance here.
Can anyone give me a recommendation for a gear that will offestt this 7-8 MPH overage I am experiencing.
Thanks for the assistance here.