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I am putting a 39 desoto overdrive trans in a 37 dodge coupe. This OD trans has a solenoid ,but does not have a rail lockout switch or a governor(no provision for either). How does this trans sense engagement speed? I have manuals for the non electric B-W OD and the fully electric B-W OD for 1940 and up, but the 39 B-W OD seems to be the cross over year and I can find no info at all. Any help will be appreciated.

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Sorry I can not help you with your problem however I noticed that you said you had a copy of a OD manual for non-electric. Would it happen to be for the 1937-38 manual version of the DeSoto OD? I am rebuilding one and I am looking for any and all information I can find on this version.


ps. fifthaveinternetgarage.com may be of assistance

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  • 1 month later...

The '39 overdrive engagement works in the same way as the previous overdrives where at and above a minimum speed a set of governor weights are thrown out by centrifugal force inside a rotating drum.

The governor weights actually operate a set of rectangular pins that are then forced out into corresponding rectangular slots in the rotating drum.

Once the rectangular pins engage in the slits the transmission is considered to be in an overdrive operating mode.

The '39 had an electrical switch mounted on the carb that had a set of contacts that were then closed when the gas pedal was pushed all the way to wide open throttle.

One side of the switch has battery volts on it and if the switch was closed this battery volts would then be relayed via a wire to one of the terminals on the solenoid on the side of the overdrive.

The solenoid would then be momentarily energized and would draw the sun gear pawls out of engagment with the sun gear in the overdrive.

In order to allow this to happen the ignition primary circuit was momentarily interupted so that the engine would come off load and miss fire at that time whilst the overdrive was droping back into direct drive.

Very similar to a kickdown on an auto.

Instead of a switch on the carb you could use a non locking lever toggle switch, as I did, and once it is flicked the overdrive drops out and you have very good acceleration. Lift off the gas again and the overdrive engages again.

The above is a very quick summary of how everything works.

I have some detail of the solenoid and the '39 overdrive explded view but only have to find it and scan it


John Spinks

Aussie 1936 Chrysler Airflow C9 Coupe

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  • 4 years later...
  • 1 year later...

Call George Asche at 814-354-2621. He rebuilds them and has a wealth of information about them. I am looking for a 39 for my car. I have a 37 De Soto that George rebuilt for me that I am going to put in my 38 Dodge if I can not find a 39.

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  • 3 weeks later...

Just a small thought regarding the overdrive kick down switch -- Hudson, and maybe Nash, used a small push button style switch that was positioned directly under the gas pedal. Perhaps that might be a discreet substitute for the carb mounted switch. All that would require is drilling an appropriate size hole through the floor board.

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