Overdrive for D25?

[bamfordsgarage]

We've recently completed a 5,400 mile road trip in our faithful '47, at an average 50-55 mph (on roads much better than this NV track). I've owned this car for 17 years, and this is the first time it's been further than 100 miles from home.

An overdrive would be nice for future long trips.

What I've read on this site and elsewhere suggests that a transmission-with-overdrive from a later Mopar-flathead ought to be a straightforward swap. (I don't have fluid drive.)

Is this correct? What particular years/models should I be on the lookout for? Can anyone suggest good links to further information? A source for the hardware? Any other comments? Thanks!

[Jim Yergin]

You might want to start by checking out the transmission section of Blueskies' web site

http://www.50plymouth.com/

Jim Yergin

[Brendan D25]

Welcome to the forum, nice to see another D25. Have you considered a rear end swap with better ratio for the highway? It might be a lot cheaper than od. There has been a lot of discussion on this previously and a chart should be around to tell you what fits. Brendan.

[bamfordsgarage]

Thank you Jim and Brendan for your replies. The 50 Plymouth link was excellent.

From Kraus' Standard Catalog of American Cars 1946-75, it appears that 3-speed O/D transmissions were available on the following brands and years:

DeSoto 1952-56, Dodge 1953-56, Plymouth 1952-56.

Do I have this correct, and can anyone confirm, or otherwise, that these devices ought to be basically drop-in to my 1947 D25?

[Young Ed]

Years look correct. The desoto and dodge ones were usually fluid drive variants and have a longer input shaft. That can be swapped to the ply version and then used.

[Californian]

There is more to putting an overdrive unit in a vehicle that never had one, I found out with my 48 Plymouth with a 230 had a loss of power with a 3:7 rear end and in OD, until I put a 4:11 rear end in and then it cruzed at 70 in OD and I have had a 51 Plymouth with a 230 an a 3:7 rearend that cruzed nice at 60-65

....I agree with Brenden D-25 that changing your third member to a higher gear ratio may be less expensive..and produce the quickest results. These third members have a flat spot on the case that has the gear ratio stamped on it...and there are different axle splines after a certain year, check a Hollander Interchange book , also those Pilot Shafts can have a diferent count on the spline for the clutch disc and the clutch gear inside the trans on that pilot shaft was changed over the years...I believe it all hapened when they went from strut to pin style syncros in the transmissions This is where Hollanders Interchange book comes in handy..

Tom (08)