# Speedo Gear Change/Chart/Color Codes



## Tom L (Aug 11, 2011)

Hello all.
Can some here tell me where to find the info pertaining to changes needed in the speedo drive after a rear end ratio change. My car build sheet says 3:53 but doing the math with rpm/speedo reads and tire diameter I am sure it now has a 3:90 rear gear. Build sheet also states M20 wide ratio, and was told this is correct as the M20 wr had no drain plug. Is there info available that states what color speedo gear is needed for this change with out doing a long mathmatical formula shown in Ames Catalog? Thanks. Tom


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## GTO JUDGE (May 14, 2005)

You do not mention year of your car. Check the links below using your cars year and such. Will vary on year, tire choice. The last link should tell you what you want to know. 
Edit: Looking at your car: 1964, according to the chart and tire size you are either a Green 18.6 tooth or Black: 17.6. The part number is listed. Questions on it: [email protected] 
:cheers


Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4

Speedo Gear Selection

Speedometer gear charts


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## Tom L (Aug 11, 2011)

*Speedo Drive Gear*

The gear is a 19T and natural in color, tire dia about 25 1/2-25 3/4 inches. Looks like I need to go to a lower number of gear teeth as the charts state. There are two listed for the 3:90 rear gears. Yes it is a 1964 and while driving going on the tach and speedo reads I am about 59 mph at 3100/3200 rpm if one can say for sure those two gauges are dead on correct. Care to make a suggestion as to which of the gears in the charts for the 3:90, 1964, 4 speed? Thanks, Tom


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## GTO JUDGE (May 14, 2005)

Tom L said:


> The gear is a 19T and natural in color, tire dia about 25 1/2-25 3/4 inches. Looks like I need to go to a lower number of gear teeth as the charts state. There are two listed for the 3:90 rear gears. Yes it is a 1964 and while driving going on the tach and speedo reads I am about 59 mph at 3100/3200 rpm if one can say for sure those two gauges are dead on correct. Care to make a suggestion as to which of the gears in the charts for the 3:90, 1964, 4 speed? Thanks, Tom


Well if you are asking me to pick, pick the opposite of the one I'd pick. That is my luck <dayum> Have you checked your speed with a GPS? This will tell you how far mph you are off at 60 mph. I have 3.55's and tach 27-2800 at 55mph 2800 at 60. I am off 2mph at 60mph. Spot on until 55. 

Try contacting them they should be able to fix ya up on the phone.


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## Tom L (Aug 11, 2011)

GPS? LOL I am part Finlander and it is said we have iron pyrite imbedded in our noses so I never seen the need for a gps.  I'll have someone in another vehicle help me with a speedo check. I thought 3200 on the tach was a little high for the speedo reading. It's not a top priority but I had the transmission out so thought it would be a good time to get the correct gear. Thanks Judge.


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