Trying to figure out my rear end ratio on my 66 442 Holiday coup that was originally an automatic, which I’m converting to a four speed. Doing this without the car as it is in the body .shop.
I attached a pic of the data plate.
My research tells me a 3.55 ratio is the best match as this will be a daily driver car. May add posi.
Thoughts anyone?
Tom

 

A M20 wide ratio trans with a 3.23 rear axle makes for a great driver.

 

I think one should determine how they are using the car 1st. Race? Long distance driver? Street?? the 4 speed will have a fixed 4th gear ratio and No overdrive. I have a 3;91 ratio that I live with due to originallity but I sure wish I has something like a 3.23 or even a 3.08 so I would be more inclined to drive it over 50 miles.from my house. note 3.42 or higher gear ratio take a different carrier.. NOTE: 3.23 was std ratio for most 4 speed with AC cars...

 

With a 3.23 or higher ratio a M20 wide ratio was mandatory with Olds. If all of the M21 Muncie transmissions were thrown in the ocean the world would be a better place.

 

In any case, unless you're going 4.33 or lower, steer clear of the M-21 close ratio, I had one in a SBC Camaro with a 3.55 and that 2.20 low made it a bear to launch.

 

If your real question is "what is the ratio currently in my car?", there is no way to know that without either finding the code stamped on the rear axle or removing the rear cover to find the tooth count stamp on the gears. The cowl tag was used by Fisher Body to install options on the car as the body was built. Fisher didn't install the rear axle and thus nothing on the cowl tag will tell you that. In 1966 the standard ration with the 442 package and Jetaway automatic would have been 3.23:1, but 3.55 and 3.90 were available options.

 

I actually liked the M21 close ratio transmission. But I liked my W-30 cam, 4.33's and L-69 too. in fact, I just bought an L-69 to use on an Olds.

 

I agree with this...Find out what your ratio is to know where to go.

 

That’s my plan when I get the car back from the body shop……….thanks for the response!

Tom

 

Yep, gotta know where you are to figure out where you want to go.