2.77 tranny spedometer gear???

[JW1965]

hey guys, I have a 1965 mustang that has an original 2.77 3 speed manual transmission. I have lost the spedometer gear, and I cant remember how many teeth it had...

can anyone help???

 

[addo]

You should be able to work backwards, if you can acquire a medium-range one to start with (junkyard, maybe). Percentage error will lead you to the correct number of teeth, as the gearing relationship is linear.

Regards, Adam.

 

[fmartin_gila]

Follow this through, insert your numbers where applicable. Using a 235/75R15 for example. 235 X 2 = 470, 470 X.75 = 352.5, Divide 352.5 by 24.5 = 14.387755, 14.387755 + 15 = 29.387755 diameter, 29.387755 X 3.1416 = 92.324571, round off to 92.33. Now divide 63360(inches per mile) by 92.33(circumferance) = 686.23416(tire revolutions per mile), now using a 3.70 ratio rear and a 7 tooth drive gear in the tail of the tranny, 7 X 3.70 = 25.9, now 25.9 X 686 = 17767.4, divide 17767.4 by 1000 = 17.7674, round of to 18(driven gear needed).
Fred

 

[gtm1086]

Had one sitting in the shop. 18 teeth

 

[JW1965]

thanks alot! I really appreciate it!

Now my next question is this:


That 18 tooth gear reads only 80% of the speed that I am going because of a rear end change.

do i need a gear that Is 80% the teeth of the 18 tooth to make it read the correct speed?


It reads 20% slow.

 

[JW1965]

i figured a 14 tooth gear, but i cant find one

 

[fmartin_gila]

I think 15 is the lowest available, you will have to change your drive gear in the tail housing to get closer. Another approach would be to find a speedometer shop, they can build a little adapter box to fit any needed adjustment. Somewhat pricey though.
Fred