'39 Chry overdrive

[plyroadking]

Hi, I have found a 1939 Chrysler overdrive unit locally and wondered if anyone knew anything about these, I have several mid to late 30's Plymouth owners that want to know if it will fit in their cars. I believe it is a column shift but I have heard that its a 38 top loading trans with an altered top unit so it can be shifted with the column linkage. I have rebuilt several R-10 units but have heard that these are real different. Any ideas what all it will fit and what its worth? Thanks!

[greg g]

This was written by a frequent contributor to this forum (haven't heard from him in a while) to an OD question on an AACA board. It may answer your question or add more to your confusion.

The overdrive tranny was developed by Chrysler during the Airflow years, based on an invention they purchased from a man named Keller (not Kaufman Thuma Keller who suceeded Walter P. as President of Chrysler), and referred to it as the "Keller Clutch".

It was first offered on the 1935 Chrysler & De Soto Airflow. The first versions were entirely centrifugally operated, with no kick-down provisions.

The semi-electric overdrives came along in 1939 (the R-7, among others), and featured an electric kick-down circuit activated when the throttle was floored (say for passing or hills).

Later (postwar) OD units added an external governor to the kickdown solenoid, and the unit pretty much remained thus through the '60s.

Walter P. Chrysler did not want to invest the production captial to tool-up and make the overdrives in-house, so they patented the device and licensed Borg-Warner to manufacture it for Chrysler (and any one else who wanted to buy it).

The 1939 and later examples basically have the OD unit as an auxiliary gearbox that replaces the extension housing of the standard 3-speed transmission, so that the entire legnth of the tranny/OD is the same as the non-OD tranny, making it a much more cost-effective option, and not requiring different legnths of driveshafts, etc.

Because there is usually a lock-out rail running from the OD case into the tranny case to positively lock-out the OD when the tranny is shifted into reverse, it is better to replace the entire transmission with an OD equipped tranny, rather than trying to adapt an OD housing onto a non-OD tranny case...it can be done, but will require a bunch of machine work.

(At least this is the case for the 1939-1954 Chrysler products...)

For whatever reasons, GM avoided overdrive until 1955 (probably the same reasons that Chrysler eschewed GM's Hydra-matic); makers that did jump on the OD bandwagon in the '30s were:

Chrysler, De Soto, Dodge(?)[ all Chrysler products from '35 thru '40, then '51-on], Graham, Hudson, Hupmobile, Lincoln (from '42), Nash(from '35), Packard(from '39),Pierce-Arrow, Studebaker (from '35),

Willys(from '42).

[Powerhouse]

If it helps at all...I have a 37 chrysler/Desoto top loader OD in my 39 roadking. Didn't require any changes except driveshaft length. Mine is non electric..i think it is an r7. Those are the ones that will swap right in ...for top loaders anyway. I haven't seen any side loaders of that model. Any pics?

[meadowbrook]

Hi.

I own a 1950 Dodge Meadowbrook and I purchased a 1940 (R7) rebuilt R 7 overdrive from Mr. Asche in Venus, PA. (great guy).

I personally like it a lot. It was a bolt on to my Meadowbrook and is simpler than the R10. It has a centrifugal OD 'switch' that, if the the overdrive cable is 'in', allows it to engage at around 45 MPH.

For passing, there is a solenoid that will disengage it, if powered by the throttle or any other means you come up with to power it.

It is different from the R 10 in that the means of activation of the OD is mechanical, with the solenoid only being powered for disengage it. The R10's overdrive is engaged by powering on the solenoid and the kickdown button disangages it. I also have read that the R10 engages the OD at a lower speed, around 23-30 MPH.

Oh, it's side loader and even that part was a direct bolt in to my Dodge.

As far as value, Asche charged me ~$200 less for it and it does have less wiring.