c42no06

I have a M-21 transmission in my 1967. My father said its a 31 spline but I think he meant 32. The rear end is 4.11. My tire size is 215/65R 15. Which speedometer gear should I be using(color/#of teeth)?

Can anyone help me.

Thank you,

chris

62Jeff

Howdy,
Check out Black_Magic's excellent tool for determining that answer
http://www.stl-vettes.com/65Vette/GearCalc.htm

Jeff

muncieman

With the combo you have you need a 26 tooth gear, and the bad news is they don't make it.

You have a 1.84 diameter gear in the trans with 8 teeth, that's all the make for the 32 spline unit. There are reduction units that were made, lot of those on GTOs. I don't know if any of those are still available.

c42no06

Muncieman,

Would using a 24 t gear with a ratio adapter of 10% slow down rate work?

thanks,

chris

muncieman

I've got a corvette parts book with all the speedo stuff in there for the later cars, I'll look and see what GM did in 71 when they used the big shaft muncie in the LT-1 and you could still get a deep gear.

I think you are on the right track. The 26 tooth gear is not perfect, it's 2 % off from the jump. Those short tires and that tall gear must be fun

I'll post what I find tomorrow.

c42no06

Thanks!