41 to 48 Hydramatic

[Steve Passmore]

Is there any way to date a Hydra-matic?  I have a 41 Cadillac with a later engine and I think the transmission could have been changed as well. There are no plates with numbers attached. Is there any other place it would have a number or any distinguishing features?

[Bobby B]

Steve,
   Hi.  What year trans do you think it might be? I've done a '47 and a '48 and there are slight differences internally as far as the drums (clutch pistons, drive pins, and # of plates), the casting numbers (1947-#8608167 & 1948-#8611451) on the case are different, and most quickly identified as 1947 "long ears" and 1948 "short ears" on the trans front lower case. 1948 was modified to accommodate the new motor mounts in the series "98" cars. The earlier transmissions  (40-42) had different rear planetary units, clutches, and lack of pressure regulator plug.   Maybe some outer casting marks can help us identify it.
                                                                                            Bobby

[Steve Passmore]

Transmission is still in the car at the moment Bobby but it is up on the lift.   Where can these casting numbers be found and what do you mean by 'Ears'?  The casing is covered in crud but I can scrap off where needed.
I have no idea of its year but the engine was changed at some time and I'm hoping they swapped out the whole thing which would have been the easiest thing to do back in the day, especially with the dowel problems they might have encountered changing just the motor.
I would like to get the auto rebuilt in my 41 coupe which still has the original 41 Hydro and it would be nice to put a later one in there if this box was later.

[Hilarius]

Steve,

don't know if it helps. Here are a few pictures of a trans that is definitely 1948.
Cleaned and seen from the side and from behind with the extension missing and the latter separately photographed.
Plus one picture of the assembled Hydramatic.

Hilmar.

[Steve Passmore]

Thanks for that Hillmar. I can see that even the later ones had the plate attached. I will have to pull this tranny and get a better look.

[wbdeford]

I have a '47 with casting number 8608721.  And a '50 Oldsmobile with 8611716.

[Steve Passmore]

Where is the casting number William?

[wbdeford]

Steve, see Hilarius' picture.  It is on the right side of the case in large numbers.

[wbdeford]

Here it is on my '47.  I had to clean A LOT of gunk away to see the numbers.

[Steve Passmore]

This is really odd. I do not have any number in this position nor do I have the raised casting which would have taken the riveted plate. Curiouser and curiouser!

[wbdeford]

So am I (curious)  Can you post some pics?

[Steve Passmore]

Heres where mine should have the raised casting for the date plate and the casting number???

[wbdeford]

I guess it's possible they put in somewhere else in earlier years.  Pics of other side, including the side pan, linkage, etc?

[Steve Passmore]

I have a 41 hydro in my coupe Bill and that has the date plate where it should be so it can't be an earlier box. Picture attached of the other side which is all tin ware so nowhere here for casting numbers or plates??

[wbdeford]

Just looking for differences....see the indentation in the lower right on this pic....I can't tell from your first pic if yours has it.  '47, '48, and '50 have it.

[Steve Passmore]

Just checked and mine has that but only half the size as yours and Hilmars?

[jackworstell]

I have had over the years maybe a dozen 1940s Hydramatics ( but none now )

Here's what I remember

Post WW II units had an oval tag on the side...which pinned down year and Hydramatic model and SN....most Hydramatic manuals include tables for decoding the info on these tags.
Pre WW II did not have oval tags.....SN number was stamped into a machined surface.... rear of transmission case.....perpendicular to axis of the unit. You could tell from this number whether 1941 or 1942.

Pre WW II tail shaft was straight- tapered     Post WW II units had a "ring" cast ( concave cross section ) into the tailshaft toward the rear of the tailshaft.....

Pre WW II units had the oil pan drain plug in the rear of the pan.    Post WW  II the plug was in the side of the pan ( I don't think I have this reversed but maybe I do ).     

Post WW II had a large hex plug sticking out of main case toward the front.....part of the oil pressure regulator mechanism.   Pre WW II....oil pressure mechanism was totally inside the unit

Jack Worstell  #7558

[Steve Passmore]

Thats some interesting and useful observations Jack.     From my little knowledge I can only question one of your points about the oval plate.    My 1941 coupe has a hydro-matic with the oval plate and the words on it C 41
I believe that means Cadillac 1941.?

[wbdeford]

My '47 drain plug is at the rear and it has a large hex pressure regulator on the left side near the top and front of the case.

[jackworstell]

Steve... Of course I can only relate what I have seen......it could well be that somewhere along the line Cadillac started  adding the oval plate to the pre-WWII units.     ( but for example.... I am absolutely positive that a 1942 unit I had did not have the oval plate.....a transmission parts vendor I ordered parts from insisted on data from the oval plate....I tripled checked and could not find one nor where one could ever have been mounted....but there was the SN on the machined surface on the rear face of the main housing......)

C 41 sure sounds like a 1941 Cadillac unit .....

Does your unit have the large  hex plug sticking out of the main case up toward the front ?     The tailpiece....straight uniform taper or a "ring"   ( concave cross section ) cast into it near the end ?

By the way ...in my first post I got  the oil pan drain plug locations mixed up......it was on the rear of the pan on the pre WW  II units....on the side of the pan on post WW II  units.

Once you drop the oil pan......the difference is quickly obvious.....eg the pre WW II units had a front oil pump that was gear driven...once the oil pan was off you could reach in and unbolt it with minimal  dis-assembly of the rest of the transmission.......Post WW II units the front oil pump was an eccentric type...... you had to remove the transmission from the car to get to it.....after first removing the fluid coupling.    Also...pre WW II once oil pan was off one of the first things you saw was the oil pressure regulator spring...post WW  II the spring was in a cavity in the main case...couldn't get to it just by removing the pan.

Jack Worstell   #7558