The Stovebolt Site Forums The Shop Area Driveline 4 speed manual tranny

Hello everyone. I am looking at changing my transmission to a four speed.I am driving a 55 second series 3200 6 235 with a 3 speed on the column.
The numbers on the side are 2 GM 591953 T.
I am asking for some help to see if this tranny will work.
Mike

added a picture of my 55 1st series restored in mid 90's it had same 4 speed tranny loved it

591953 is the casting number for a SM420 transmission. It should work OK. The previous owner of my truck switched out the 3 speed for a SM420. I replaced that transmission with a 1967 SM420.

BTW, the picture you wanted to post is not showing.

Thank you for your response. The pick was 7.2. and only up to 5 works. It also has a tag on it that say's E25 it is to the right of the 2 is that the date.?
2 E25
GM
591953 T
That is how it was stamped.

Changing from a 3 speed to a SM420 or any other HD 4 speed will require a completely different driveshaft.
If I remember correctly a 3200 will require a 2 piece shaft with a center support bearing.
It will also require a taller center floor cover. Both transmissions are 1 to 1 in high gear so it will not
improve highway speed.
Fred

Thank you so much for your information. I had one in my 1955 first series 3/4 long bed that I had. I will get the drive shaft out of the truck it came in as it's still there, thanks again. Do you know what the E25 stands for on the transfer case is that the date it was manufactured. If anybody knows please chime in.

Mike

Post a picture of the E25 so we can see what your looking at.

Mike B

Hello Mike I tried but the picture is 7.2 mb and all we are allowed is 5mb. I will take another Picture tomorrow

If the picture was taken with your phone, you can email it to yourself and it will automatically reduce the size, then copy and save it from there.

Mike, Just a suggestion but give those number a good scrub with a wire brush before you retake your picture. The casting# 591953 was used as the main case for 1948-63 according to a quick search of GMPartswiki.

Thank you so much.

Mike

Awesome thank you Phil

Thank you Dan for the info and the link. I scrubed it with aa wire brush before I took picture (-:

Mike, while we wait to see the new pic of your casting numbers mentioned above, you should take another look at a different point on the transmission case. The pic below shows the location of the "stamped" transmission unit serial numbers on the SM420 4 speed, as indicated in the 1955 2nd Series Truck Shop Manual. Take a picture of yours (wire brushing/cleaning as needed of course) and post that picture too. Once we have both pictures to review,we should be able to best pinpoint what you have.

I posted a picture on the opening thread post. all of you are a lot of help thank you for taking the time it's greatly appreciated.

Mike

I spent about 3 hours cleaning and wire brushing I am going to take another picture like you said and will post it in a an hour or so today thanks.

Mike

If GM followed previous conventions on casting codes, that E 2 5 might be a date code signifying April May 2, 1955 (or maybe 1965). That plate where the E 2 5 appears was on a small plate screwed to the sand casting form each day, leaving the impression on the sand mold when the case was cast.
But according to the 1955.1 and 1955.2 Vehicle Information Kits, 2-speed transmissions were identified with Plant code T (for Toledo Plant) and then a number for the month and a number for the day of the month. So I don't think that would make your transmission a 1955 year build. Unfortunately the 1965 Vehicle Information Kit doesn't provide codes for engines and transmissions like the earlier ones do. There may be a serial number stamped on the right rear of the case (likely on a machined surface) that might provide a clue to when it was built.
[on edit] fixed the month (can't count letters correctly ) Also, the SM420 was replaced by the SM465 in 1968, but the casting number changed after 1963 like Dan found.

Mike, I see the picture now added to your first post in the thread. All that info is clear thanks to a very thorough cleanup. Here is a breakdown of what "I think" that info means:

2 = The assembly line at the plant (I think)

E25 = E = May / 2 = 2nd day of May / 5 = 1955 (This is using what we know of general GM casting date codes as far as I know)

GM = General Motors

591953 = SM420 main case casting ID code as noted previously above - 1948-63

T = Toledo (Assembly Plant)

Others will come along and confirm or offer more on my info as they may have more knowledge than I.

Finding and posting the actual "stamped" unit number should help confirm what is listed here. Will watch for further pics and updates.

PS - The good news is YES it will work for you with the needed driveshaft changes!

Here's what the 1955 Vehicle Info Kit says about the Transmission Identification Code. Doesn't match the E 2 5 code on your transmission.

But like Dan said: It'll work for you.

Mike, The "stamped" number you are looking for on the back right corner of the main case is below where the shift tower assembly mounts to the case. See the arrow pointing to the "vertical" surface just below the shift tower where the stamping will be in a screen grab of your last picture added and another one of the Shop Manual pic mentioned above.

The stamped unit number corresponds to the information Kevin posted from the 1955 Vehicle Info Kit.

Thank you so much Dan and thankfully I can get the drive shafts off the same truck.

I had a 55 1st series that I restored back in the mid 90's it had the four speed also loved that truck drove it for many years,

Mike

thank you Kevin appreciate it.

Mike

The I22 on the cover is the cover date code;

I (eye) = September
2 = day
2 = year (could be 1952 or 1962)

Mike B

Thank you Mike

Hello Fred is there a forum post that has some helpful advice on the 2 piece drive shaft with bearing. I have a cross member at the back of my cab Is that wher I can put the mounting bracket at. I took the brackets of the 1 1/2 ton truck. Appreciate any help.

Mike