1940 overdrive transmission

[270]

Can anyone tell me where I can find information on this Chrysler trans. Its a 3-speed manual overdrive unit pulled out of a 1940 Chysler New Yorker. I would like to install it in my 40 Plymouth. I presume at a certain speed centrifugal force puts it into overdrive when the dash lever is pushed in. It doesn't seem to have a govenor like the newer 50s overdrives have. It does have the kickdown solenoid on the side. I believe these units operate differently than the unit I mentioned earlier. Thanks `

[Guest De Soto Frank]

Yes, it is different than the Post-War OD trannies.

I think you probably have an R-7 tranny: look for a raised (cast) number on the left side of the OD housing... you should see an "R" followed by another number: this is the model of the tranny.

At the parting line between the tranny case and the OD housing, in the left side, there should be a flat boss with a number stamped into it: this will begin with the vehicle code for the origanl application of your tranny: if from a 1940 Chrysler NYer, it should have " C - 26 " stamped there, followed by the tranny serial #.

As for putting it in a '40 Plymouth ? You might need to change the input shaft if the NYer had Fluid Drive, as the input shaft will be far too long for a conventional "Dry-clutch" car.

You will also need the lock-out cable, and a kick-down relay (also different than the post-war stuff), as well as some sort of kickdown switch: the factory set-up employed a switch that was either part of the carb or part of the throttle linkage: either way, the driver had to floor the accelerator for kick-down... it's not a subtle experience. ( Grab all these parts from the donor car, if you can!)

The R-7 is known as a "semi-electric" OD; this is the second generation of OD trannies (R-10s belong to the third (and fairly final) generation of ODs). Upshift is achieved by centrifugal weights & springs inside the unit. Downshift occurs by sufficent drop in vehicle speed or by activation of the kick-down circuit, which involves the relay and the solenoid. There is no external governor.

I have an R-7 from a 1940 De Soto (S-7) that I plan on putting into my '41 S-8, after I get the front suspension rebuilt...

Hope this helps some...

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[270]

Thanks for the info Frank. This was definitely out of a stick shift car, I know this is a good swap,and it can be done. I just didn't have any info on operation and how to drive it. Do you know where I can find 12 volt solenoid. The other Question is, do I have to use the kick down option? I understand the load must be taken off the trans in order for it to come out of overdrive,thus grounding out the ignition for one revolution. Iam not to keen on that. What if you pushed the clutch in then hit the kick down button? Or just use OD when your highway driving. Thanks again. Rich

[jrbartlett]

What OD transmissions did the '38 Imperial and Royal use?

[Guest De Soto Frank]

I believe the '38 & earlier cars used the "centrifugal overdrive"... these were floor-shift units, with a lock-out control cable.

The upshift/downshift in & out of OD was achieved purely by the centrifugal weights in the OD.

There was no "kick-down device"... I suppose it would have been possible to do a "forced downshift" by clutching and shifting out of OD using the control cable...

The '39-'41 R-7 OD ( "semi-electric") was the next evolutionary step, and added the electric kick-down feature.

The post-war units (R-9, R-10) were "full-electric", with a revised control system that employed a governor, and used the solenoid to upshift into OD(and keep it there), the opposite of the R-7 system. I believe this version of the OD stayed around through the 1960's...

It is kind of interesting that Chrysler Corp (who pioneered this type of overdrive, with the Airflows) abandoned it from 1941 through 1948; I guess this was due to their emphasis on their new Semi-automatic trannys... the semi-auto and Fluid Drive cars usually had the highest rear-end ratios of Chryco products (permitted by the "slippage" of the fluid coupling), usually 3.54 for the sixes and 3.36 for the eights. Having these ratios meant the cars could cope with highway speeds ( 50-65mph ) much better, w/o the need for an OD.

Chrysler did begin offering an OD option in Dodge in '49, and in De Soto with the '52 V-8...