1940 P10 Transmission

[DSchreiner83]

Hi All -- First ever post... I have a 1940 Plymouth Deluxe that is pretty much entirely original. It has the original 201cc and 3-on-the-tree transmission. I would like to upgrade the tranny to try to eke out a reliable 55-65mph top speed. Is this possible while maintaining the original engine? Is there an overdrive that would pair relatively easily with the 201 and 3-speed?

Thanks! 

[Sniper]

My 51 with the same basic drive train doesn't have a problem doing 55, I've had it to 70 but it's hollering there.

 

I do have 3.91 rear gears so that might be different

Edited November 29, 2022 by Sniper

[Young Ed]

Likely that one has a 4.1 but if it retains it's original 16" wheels it should be the same result as your 51. 

 

You need to rig up a tach and see what RPM you're really at before changing anything 

[Loren]

In May of 1952 Plymouth began using the Borg-Warner R10 Overdrive.

Your 1940 is the first year of “3 on the tree” so yes it will fit.

You can check the rear end gear ratio online for you car and double check it under the car.

The housing has the ratio stamped under the filler plug.

Ratios are available to 3.54 which with an Overdrive would need a strong engine or a light car.

It is my personal opinion that a properly working R10 Overdrive really benefits a Plymouth.

Even at 55 mph the car is so much quieter because the rpm drops 30% in Overdrive.

 

BTW don’t throw away your 1940 transmission. That’s the one with desirable 2nd gear ( the only optional gear ratio in 2nd )

[Sam Buchanan]

Once you determine the rear end ratio you can calculate rpm with a calculator like this one:

 

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

Edited November 29, 2022 by Sam Buchanan