1940 Cadillac Flywheel/flexplate identification help please

[thebeebe5]

Greetings all.  My first post here.  I didn’t see an introduction forum and I hope I’m not breaking protocol by my initial post here.  I’m not a Cadillac LaSalle owner or authority and this is why I’ve come here for assistance.  Hoping someone can point me in the right direction.
I’ve recently acquired an old flexplate.  It’s quite heavy.  Not a flywheel in the traditional sense for sure.   I was told it fits an early 40s Cadillac.  It was encased in cosmoline and I was told it is a NOS part.  It cleaned up like new.   Still needs a bit of attention after being dipped to disolve the cosmoline away, but that looks like minor solvent tank and stiff nylon brush work.   No rust or other damage/signs of use.

Can anyone help me positivily identify if it’s a Cadillac part and what it fits? 
Sincere thanks in advance!

Jim B.

[Chris Davis]

The set screw type drain plug and welded on "fins" make me think this is WW2 military hydramatic.

[thebeebe5]

The set screw type drain plug and welded on "fins" make me think this is WW2 military hydramatic.

Thanks, Chris.

Any idea what it might have been used in? 

[savemy67]

Hello Jim,

In WW2, the Hydra-Matic was used in the M5 Stuart, and M24 Chaffee tanks (as well as some other armored vehicles).  Two transmissions were used in the tanks - one for each track.  The Stuart was a "light" tank weighing 17 tons, and the Chaffee was a "light" tank weighing 20 tons.

My '41 Cadillac Hydra-Matic manual has a photo of the flywheel.  when I look at your photo and the one in the manual, the flywheels do not look identical, but that could be due to the quality of the photos.  In general, your flywheel (which is what Cadillac called it in the late '40s and early '50s) could be for a Hydra-Matic from '41 to '55 or so.

Do you have the rest of the transmission?  If not, what are your plans for the flywheel once it is clean?

Respectfully submitted,

Christopher Winter

[thebeebe5]

Hello Jim,

In WW2, the Hydra-Matic was used in the M5 Stuart, and M24 Chaffee tanks (as well as some other armored vehicles).  Two transmissions were used in the tanks - one for each track.  The Stuart was a "light" tank weighing 17 tons, and the Chaffee was a "light" tank weighing 20 tons.

My '41 Cadillac Hydra-Matic manual has a photo of the flywheel.  when I look at your photo and the one in the manual, the flywheels do not look identical, but that could be due to the quality of the photos.  In general, your flywheel (which is what Cadillac called it in the late '40s and early '50s) could be for a Hydra-Matic from '41 to '55 or so.

Do you have the rest of the transmission?  If not, what are your plans for the flywheel once it is clean?

Respectfully submitted,

Christopher Winter

Christopher.    Excellent info.  Thank you!

I work at an engine machine shop on weekends (my “decompress from real life” job) and disassemble engines, grind valves, build my own stuff and make parts for builds as required etc..
I also like to make things....   I picked this up as a potential base for an ashtray.   Usually I get my hands on old worn out/well used parts, but thought perhaps someone might be needing a part this nice for a restoration.   Thought I’d try to figure out what it was and what it fit (and if it was worth anything) before I turned it into “art”....
The fellow I got the flywheel from has two transmissions and an early 40s Cadillac engine he offered me really cheaply.   I could go back and get them I suppose, but I’d only be interested in the engine personally.   The transmissions were rather unwieldily. Not sure I would use/build them for any hotrod projects....

[Chris Davis]

Adding to the discussion, the hex plug (per my Master Chassis catalog) is unique to 1940 & 41.  I don't know about Oldsmobile but guess they are the same.  FWIW, the hex plug is present on my 41 hydramatic flywheel but not on the 46 or 49 flywheels I had.  Plus none had "fins" on the flywheel. 

The military manual for  tank, gun carriage, and armored car servicing (TM9-1727C)  shows the hex plug as one of the transmission drain plugs (the other being the cooling water connections).  The manual has no photos of the flywheel without the torus attached so its anyone's guess if it has "fins" on the inner face.


As an aside, the 1944 factory issued passenger car hydramatic training manual makes no reference to the fins that are shown in the 1941 hydramatic service manual.


Hope this helps

[thebeebe5]

Adding to the discussion, the hex plug (per my Master Chassis catalog) is unique to 1940 & 41.  I don't know about Oldsmobile but guess they are the same.  FWIW, the hex plug is present on my 41 hydramatic flywheel but not on the 46 or 49 flywheels I had.  Plus none had "fins" on the flywheel. 

The military manual for  tank, gun carriage, and armored car servicing (TM9-1727C)  shows the hex plug as one of the transmission drain plugs (the other being the cooling water connections).  The manual has no photos of the flywheel without the torus attached so its anyone's guess if it has "fins" on the inner face.


As an aside, the 1944 factory issued passenger car hydramatic training manual makes no reference to the fins that are shown in the 1941 hydramatic service manual.


Hope this helps

It does...   kinda.  LOL

LOADS of different details.    Might help if I had a clue about Cadillac, but this part is my first exposure.
I’m thinking I may go get the engine that fellow had.  1941 or 1942 I think he said.

Could be a fun build...

[Tom Boehm]

Hello Jim, Is there a part number stamped anywhere on it? Some of us have parts books from that era and could look it up.

[thebeebe5]

Hello Jim, Is there a part number stamped anywhere on it? Some of us have parts books from that era and could look it up.

We can find nothing of a part number.  🤷🏻‍♂️

[The Tassie Devil(le)]

G'day Jim,

You have an email from the Moderators that requires your attention.

Bruce Reynolds,
Forum Administrator.