Transmission Interchange Question

[David Conwill]

Hi Folks,

 

As I stated in my introduction, I’m in the planning stages of a ‘40s-style hop up based on a Dodge Brothers roadster and using 90%+ period MoPar content.  After missing out on a complete engine / trans setup from a ‘38 Dodge passenger car, I’ve started thinking about other sources for a floor-shift 3-speed for this project.

 

1938 Dodge engine and trans

 

I was already planning to use the steering box, column, and wheel from a Job Rated truck, and it occurred to me that these vehicles used floor-shift boxes as well.  

 

1942 Dodge truck floor shifter

 

Were the ‘39-‘47 truck three-speeds related to the ‘37-‘38 passenger-car boxes?  How do the ratios compare?  Can you swap parts around?

 

Any help is appreciated!

 

Regards,

 

Dave

[Jerry Roberts]

Well here is a little information ;  The 3 speed 1939 - 1947 Dodge truck transmission were not synchronized until 1941 , and then  only 2 nd & 3 rd gears . 

[David Conwill]

I don't believe any manual transmission had a synchro first until Ford introduced the 3.03 Toploader in the mid-'60s.  But I certainly am not looking for a crash box.  Thanks!

[wayfarer]

If the top shift is important then why not go one step further and use a 4/5 speed OD? There are plenty late model units

that should be good candidates and then you have a few more options for rear gear....besides, who will see it?

[Young Ed]

These are the ratios I have for 41 truck 3spd. 1^st – 3.3 to 1;   2^nd – 1.78 to 1;   3^rd – 1.00 to 1.    Rev. – 4.3 to 1.

[David Conwill]

If the top shift is important then why not go one step further and use a 4/5 speed OD? There are plenty late model units

that should be good candidates and then you have a few more options for rear gear....besides, who will see it?

 

It's not entirely off the table, but my ideal is to do a 100% period-correct build using no parts newer than 1948.  Think of it as a restoration of a car that never existed, but could have.

[David Conwill]

These are the ratios I have for 41 truck 3spd. 1^st – 3.3 to 1;   2^nd – 1.78 to 1;   3^rd – 1.00 to 1.    Rev. – 4.3 to 1.

 

 

I found a helpful old Plymouth shop manual, circa 1942 that covers cars back to 1936 and here’s what it had to say:

 

1936-40: 1st - 2.57 to 1; 2nd - 1.55 to 1; 3rd - 1.00 to 1.  Rev. - 3.48 to 1.

1941-42: 1st - 2.57 to 1; 2nd - 1.83 to 1; 3rd - 1.00 to 1.  Rev. - 3.48 to 1.

 

The transmissions seem to be nearly identical in most other respects with the following exceptions - 1936 used a bronze bushing on the idler shaft, and 1937-42 used a roller bearing; 1936-39 had no bearing or bushing on the transmission extension, whereas the ‘40-‘42 boxes had ball bearings; lubricant capacity increased by ½ pint after 1939 to 2-3/4 pints; and the obvious change from floor-shift in 1938 to column shift in 1940 (1939 was the first year for column-shift, but only on P-8 models; P-7 retained floor shift).  Additionally, by some accounts the synchros on the 1939 P-7 box are superior to the slower-shifting ‘36-‘38 transmissions, so this would seem to be the ideal box.

 

Unless, that is, you can put 1940 passenger-car gears into a 1941-47 pickup case.  Still not clear on whether that can be done.

Edited May 18, 2015 by David Conwill