VCCA Home Forums TECHNICAL - 1945 AND NEWER 1955-1957 3 speed stick question

Because of my interests in certain years, my parts books only go to 1957.

Looking at 3 speed transmissions, 3740406 is the number for 1955 thru 1957 6 cylinder. Does this part number go BEYOND 1957 ?

Same question for 3 speed 3751220, which is 1955 through 1957 8 cylinder. Does this part number go beyond 1957 ?

Does anyone have casting numbers for the above transmissions ?

Finally, what is the difference between the above 6 cylinder and 8 cylinder transmissions ?

Thanks for any and all assistance.

3740406 transmission assembly is for a replacment transmission for a 1955-1957 car with 3 speed.
3751220 number was removed in 12-57.

3845122 was the casting number for all 1955-1957 3 speed non overdrive transmission cases..Note though the 3 speed close ratio had that casting number but if I remember correctly the rear opening was larger. Also overdive trans. had that casting number but had a hole driled in the rear of the case for reverse lock-out in the O.D> unit.
Also 1955-1959 3 speed trucks had that number but something in the case was drilled or machiened in a different manner.

The only difference between a 6 Cyl. and 8 Cyl. car 3 speed was the main drive gear. The shaft portion of thee gear was slimmer for the 8 Cyl. but made of a stronger steel. The two shafts will interchange and I never saw a 6 Cyl. break when used in a 8 Cyl. application.

I would say in the end if you bought a new transmission in 1959 (for a 1955-57) you got a 1957 8 Cyl. unit (or perhaps a 6 Cyl)

Above is from a 1959 parts book and my vanishing 1957 knowledge.

In 1958 the same basic trans. was used with minor changes but gears the same EXCEPT the 283 had semi-close ratio
gears ( except over drive) and the 348 had a full close ratio....in 1959 the 348 went to the semi-close ratio.

The same basic trans. was used up thru 1965

I should mention that the transmission dates back too 1937 with some changes in 1940,1949, 1953 and 1954.
Was the Corvette trans. in 1956 (close ratio version) and standard in Vettes for many years after the 4 speed became an option.
Was the standard (non-option) trans. for 409 cars.

Gene,

Thanks for the information and insight. I understand the concern for the vanishing knowledge.
No such thing, in my house, as watching a "rerun" on TV.
With my lack of memory, everything is a "firstrun".
Here's my concern:
I have two 1951's, one is basically stock, the other has a modified "open driveline", but still with a 235 6 cylinder.
The modified one came to me, through the estate of a friend.
The driveline is meticulously updated, looks like an original installation, but, of course, it is not.
The transmission is from a 1959 Chevy, a 3 speed manual, with functioning overdrive.
The rear in this '51 is a F**d 9", with a 3:50 positraction ratio.
Rather than swap the rear to a 4:11, I would rather remove the overdrive transmission, and install a non overdrive, standard 3 speed stick transmission, thus my question about what will fit.

The 1959 O.D. trans assembly (and 4 speeds) are the same length as a 1955-1957 transmission O.D. or not.

OK, many thanks.

One more thought here, Gene, would the input shafts be the same length on the trannys you mentioned ?

Length wise yes.

Thanks.

Hi Bob,
Dumb question, but would it be more problematic to find a set of 4:11 gears for that "Brand X" rear end??

Probably talking out my south bound end. LOL

If it were mine I would do everything possible to keep the overdrive.

Rick and Gene,
A lot of time and money went into this overdrive conversion.
The cost of the rebuilt 9" with 3:50 positraction, plus the price of the rebuilt 1959 overdrive tranny made this an expensive conversion, but that was always the mindset of my late friend, to do it right or not at all.
The problem came to light, after the fact, by using the 3:50 ratio.
To convert to a 4:11 is more money than I have or want to spend, thus the idea of going back to a straight, non o.d. tranny.

Understood, read reply to you and Rick.

Having the overdrive is not a problem if you do not use it. If the consideration is regarding resale then it becomes a different matter as it probably is underpowered when in overdrive and is a rocket ship downhill. The overdrive tranny most likely has a good resale value and possibly enough to cover the cost of replacing it with a std three speed from say a 54. I think it would be an easier and less expensive job to change the tranny than the axle ratio. There is a 53-54 std. tranny on Craigs list in the Boston area right now for $75.00 so if it's a straight bolt in then that would be the way I would go.

This '51 of mine (I have two) that I am speaking of has been modified by my late friend.
It has a '61 235 with an open drive line, including a 1959 Chevy 3 speed stick O.D., and 9" Ford rear, so the 53-54 tranny will not work, but thanks for the reply.

I still think that a tranny change would be easier if there is a direct bolt in. Changing the driveshaft length on an open drive line is an inexpensive easy job compared to removing the rear axle for a ratio change.

Steve, going back to my initial concern, I'm looking for a standard 3 speed stick, without overdrive, to swap out with my current 3 speed stick, with overdrive.

Gene gave examples of what regular 3 speeds would fit, without modifications.

Being that the complete 9" rear is either new or newly rebuilt, with a 3:50 positraction, I do not want to consider a swap in gearing and mess up all that is new, including my skinny wallet.

The overdrive does function well, and when it is engaged, it'll run to god knows what speed on top end, but the LOCKED OUT GEAR RATIO of the O.D. tranny, with the 3:50 ratio, is sluggish, on initial acceleration.

Update: I THOUGHT the first gear ratio, in the O.D. tranny was a 2:20 ratio in the LOCKED OUT RATIO, but the actual ratio is 2:94 in first gear, in both the O.D. tranny and the non O.D. tranny. Those 2:94 ratios come from the 1959 Chevy spec sheet, based on both trannys. My O.D. tranny is a 1959.

Swapping from the O.D. tranny to the non O.D. tranny will NOT help my initial acceleration. Phooey !

A swap to a 4:11 will help. Double Phooey !