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Post Info TOPIC: Making sense of GM three speeds (s/t)
unruhjonny


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Making sense of GM three speeds (s/t)
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About a year ago I posted a thread much like this on another forum, and so far no one has been able to help. 
So I figured Id put this question out to this friendly group.

 

Can anyone help me make sense of the different three speeds that GM used, along with their transmission designations?
(EG: SM318 vs SM330 vs SM465)

 

I'd also like to list pertinent info such as number of bolts for the side cover, if the first gear is synchronized, and if it was classed as a light duty versus heavy duty gear box, or if there is something distinct which might be why it is considered a different transmission (EG: T-85 vs T-89).

 

My current list starts with the Muncie sourced SM318/SM319 which I believe started being manufactured for passenger vehicles in 1940 and was made through to 1969.
I don't see the need to list EVERY three speed known to man, but would rather touch on all three speeds that could be found in 1960's and newer GM vehicles, with some other period transmissions from the same time to spice it up.

 

What I would like to do, is try to make a list of three speed manual transmissions with a means of identifying them, and right now I seem to be stumped on two things:

1) the GM code for the 1966-1987 Saginaw three speed(s);
I believe that GM called it a SM326, but I found reference to it also being called an SM342;
My gut says there is more than one, and they have differences so maybe GM used both, and one code indicated a departure in one way or another from the other code.
I am questioning if the '342' is a non-GM designation, since companies such as Hurst (which is an easy example in this case) have given transmissions a three digit number code that is often unrelated to the parent companies (ect) designation - as seen in this link:
https://documents.holley.com/techlibrary_manual.pdf
It appears as though the Hurst designation is '343', while Borg-Warner has designated it as a '301' (I have a BW book but you have to know what youre looking at for it to make sense).
(this is a condensed version of that link)

HUrst transmission identification chart.jpg

2) The various Borg-Warner (in house) manufactured three speeds are also confusing me.
I am seeing at least a half dozen different ones, but various sites seem to suggest it was the T-16, or the T-85, or the T-86, or maybe the T-89 from which the T-10 four speed was derived;
I believe based on my research, that the T-85 was the transmission that the T-10 was derived from, and that the T-16 & T-86 are wholly different from the T-85, while the T-89 was a derivative of the T-85.
I do not know if one or more of these codes is for the same transmission.
As another point of example, this is a nice article that I found on the T-85/T-89:
https://www.hemmings.com/stories/art...-transmissions

Any assistance would be appreciated.



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1970 Formula 400
Carousel Red on black (std) interior
"no drivetrain option" car (same base drivetrain as GTO)
1:411 1970 Firebird Formulas originally sold in Canada

Luke 23: 39-43 / Ephesians 2: 8-9  / 1 Corinthians 2:12-14 / 2 Timothy 3:1-5;12
unruhjonny


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wow - this site is showing one hundred and twelve views!?
I wonder how many of those are google-bots or the like.

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1970 Formula 400
Carousel Red on black (std) interior
"no drivetrain option" car (same base drivetrain as GTO)
1:411 1970 Firebird Formulas originally sold in Canada

Luke 23: 39-43 / Ephesians 2: 8-9  / 1 Corinthians 2:12-14 / 2 Timothy 3:1-5;12
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Prefectca


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I have looked at this post several times as I would like to have information also. I do know that the Muncie 351 was used in heavy duty applications such as towing packages and big block cars and pickups. I also know that that the Saginaw 343 came in several different ratios, identified by the number of rings on the input shaft. If I remember I think there are four different gears sets in the Saginaw three speed. I think that the option codes for the transmissions would be different depending on the gear ratio.

Paul

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unruhjonny


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I have three of those (Hurst designation) "351" transmissions;
That one used the either the options codes MC1 or M13 - BUT(!!) it really depended on the model year, and vehicle.
The GM designation for that transmission was a SM330 - I tend to refer to it as a "Muncie 330"

A part of the problem is that GM transmissions are often referred to as their option codes (EG: M20/M21/M22) as opposed to their proper GM designation;
Then to make things even worse, each aftermarket company used different designation.
The Borg Warner designation for that Muncie three speed was "306".

I am often the only guy at swap meets asking about three speeds (they often show up at the PDX meet - normally by old circle track guys)...



-- Edited by unruhjonny on Thursday 20th of January 2022 01:19:04 PM

__________________

1970 Formula 400
Carousel Red on black (std) interior
"no drivetrain option" car (same base drivetrain as GTO)
1:411 1970 Firebird Formulas originally sold in Canada

Luke 23: 39-43 / Ephesians 2: 8-9  / 1 Corinthians 2:12-14 / 2 Timothy 3:1-5;12
unruhjonny


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Posts: 814
Date:
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also;
That Saginaw, as well as coming in different gear sets, could have an overdrive - this is the setup that people swap onto the saginaw four speed.
I suspect the different gear sets have something to do with the different designations I am seeing, but I haven't been able to confirm this.

Back to the Muncie three speed;
There are two distinct version:
"A" gear set; used in trucks and some full sized cars
"B" gear set; used in cars

There are setups to adapt these transmissions to 4wd trucks (they were built that way).

"A": no identifier ring on the input shaft; 3.03 / 1.75 / 1.00
"B": single identifier ring on the input shaft; 2.42 / 1.58 / 1.00

To the best of my knowledge, the "A" gear transmissions never had a tailhousing with provisions for a floor shifter - they were always column shift;
This means that one of the unique parts to the "B" transmission is the tail housing which has provisions for a floor shifter.
Other gear set specific parts are:
countershaft cluster gear
main drive gear (aka: input)
main shaft second gear
front bearing cover (trucks use a larger OD part)

I have been chasing Muncie three speed parts and information for over fifteen years - I found my first "B" gear set transmission out of Spokane in 2004, or 2006.
I have been sharing any info I have learned, to anyone willing to listen ;)
These "B" gear set transmissions were base equipment for all 1969 model year Chevrolet SS (V8) cars, as well as the Corvette for that year;
By all accounts it's indestructible.

__________________

1970 Formula 400
Carousel Red on black (std) interior
"no drivetrain option" car (same base drivetrain as GTO)
1:411 1970 Firebird Formulas originally sold in Canada

Luke 23: 39-43 / Ephesians 2: 8-9  / 1 Corinthians 2:12-14 / 2 Timothy 3:1-5;12
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