I have my trany apart and need a new input gear. It is a 21 tooth, 10 spline input...so I assume I have the Muncie M20??
Is there any advantage to the M21 close ratio over the M20 wide ratio? I'm not racing the car...just street application. I have the Type "0" differential but don't know what gears are in it. [can't seem to find the codes that are supposed to be stamped into the axle tube on the inboard, passenger side].

I can find the ratio by turning the drive shaft and counting the wheel revs...but what would you recommend for a good trany/differential combo?

Thanks

 

Just measured the differential ratio...I have the 2.78:1 anti-spin differential.

 

You don't want to run an M21 with 2.78's. You really don't want to run an M20 with it either but it will work better than the M21

 

Autogear (Google it) sells quality Muncie parts.

 

Not sure about the method you used to measure your ratio. But if you've never changed the oil in the rear end this might be a good time. Then you can pop the cover and read off the ring gear the number of teeth in each the ring and pinion, divide to get the ratio.

I had a 1968 4 speed Cutlass many years ago. It had an M21 with a 3.08 rear end ratio. In town it would leap off the line and half way across the intersection... I couldn't slip the clutch enough to make it comfortable to drive. I swapped in a 3.31 and it was much more fun. So I'd be surprised if your car had a 2.78. Not trying to be critical of your method but my experience is that you should have a 3.23 or lower ratio behind a factory 4 speed car.


John

 

My son turned the wheel ten revolutions and I counted the number of revs on the drive shaft. Thought I counted 28 revs but I'll try it again to see what I get. Good suggestion on changing the oil... Will do