transmissions for early c-3

[woobie1966]

I was talking with a member and the topic came up of transmissions, amnual to be specific. i have seen t-10's for sale and richmond 5 and 6 spds. i read that the 6 spd require rather extensive mods, the five spd requires only rear crosmember adjustments,i hadn't thought about it but the early c-3 have m-21's . how do the m-21 compare with the t-10? are they stronger, weaker ? the t-10 is rated at 450 ft/lb is the m-21 rated higher? does any one know the ratings on the 5 spd/6 spd
has any one done this modification?
thanks
mike

 

[dshanks]

Hi everybody

Hi, my name is Derrick. I'm new here, you guys will likely hear alot of questions from me in the near future, any help would be greatly appreciated. I tried to find my answer without bothering you guys but I failed. This old unanswered post seemed like the best place to ask my questions today. I have a 71 4 speed coupe, I will be in the process of doing an engine swap soon, and Im trying to cover all my bases before I disable my vette.
Is it safe to assume that I have an M-21 tranny? The car has been in my family for over 20 years and I guarantee it is stock (the only other owner was a parapalegic that never drove it). I vaguely remember reading in one of my assembly manuals that some had a Saginaw Transmission, but it was a bit confusing, maybe these were in C1s or C2s??? The assy manual is OLD, it covers 1955-1973 corvettes, so I assume the book is from from 73. This would not be the first mistake ive found in there (ex: it quotes the lowest HP option in 1971 was 300, not 270, and theres more...).
Ill climb under there tonight and retrieve the numbers from the tranny and post them tomorrow.
This leads into my other question. If it is in fact an M-21, what clutch size do I buy?

Thanks in advance!

Derrick

 

[Rowdy1]

Not Always

Your car could have had a couple different transmissions, Borg Warner, Muncie etc. I'm NOT a numbers matching guy so I don't know for sure but I'd hope someone will chime in here soon or at least after you post the #'s. I'm guessing with the engine swap you're talking about you're not going to worry about restoring the car to original? If so, you'll want to get your 4 speed rebuilt if it needs it. Depending on condition and miles and durability "if" you're going to a more powerful engine and depending on how you plan on driving it you may want a different trans. To answer some of the unanswered questions in the earlier thread, there are a few transmissions out there now that will fit in the vette that will stand up to over 600 foot lbs. are geared for performance and have an overdrive 5th gear for economy. One such company is Classic Chevy 5 Speed, they offer a couple different kits that will bolt up and actually have the shifter come up in the same place as the original which was always a problem for the early model vette's. Let's see what you have first and what your plans are.

 

[fine69]

Muncie Numbers

Hi, my name is Derrick. I'm new here, you guys will likely hear alot of questions from me in the near future, any help would be greatly appreciated. I tried to find my answer without bothering you guys but I failed. This old unanswered post seemed like the best place to ask my questions today. I have a 71 4 speed coupe, I will be in the process of doing an engine swap soon, and Im trying to cover all my bases before I disable my vette.
Is it safe to assume that I have an M-21 tranny? The car has been in my family for over 20 years and I guarantee it is stock (the only other owner was a parapalegic that never drove it). I vaguely remember reading in one of my assembly manuals that some had a Saginaw Transmission, but it was a bit confusing, maybe these were in C1s or C2s??? The assy manual is OLD, it covers 1955-1973 corvettes, so I assume the book is from from 73. This would not be the first mistake ive found in there (ex: it quotes the lowest HP option in 1971 was 300, not 270, and theres more...).
Ill climb under there tonight and retrieve the numbers from the tranny and post them tomorrow.
This leads into my other question. If it is in fact an M-21, what clutch size do I buy?

Thanks in advance!

Derrick

Hi Derrick,

Corvettes came with Muncie M-20, 21, and 22. Here's some information I had saved in my "Corvette Info" file.... you should be able to determine yours after you write down your numbers.

Muncie 4 speed serial numbers begin with the letter "P". The serial number is a date code. The code will tell you which particular year the transmission was built for.

Serial numbers from 1963 to 1966 included only the month and day. P0101 would indicate January 1st.

In 1967 and 1968 the serial number got a year designator and a letter designator for the month such as P8A01, meaning January 1st 1968.
If you have a Muncie dated with a December build date it was actually built the prior year. An example would be the date code P8T13. The T stands for December and 13 is the day. This is for a 1968 production car. This means the Muncie was assembled December 13, 1967 for the 1968 model year. To confirm this simply look at the VIN number. It will usually begin with a 18S101350 or a 28N12950. The VIN number will usually be a low number.
1969 to 1974 Muncies got a ratio designator at the end of the serial number. An example would be P4D23B. This equates to April 23, 1974, M21 ratio.

Month Code Chart

Month, Letter
Jan, A
Feb, B
Mar, C
Apr, D
May, E
Jun, H
Jul, K
Aug, M
Sep, P
Oct, R
Nov, S
Dec, T

Ratio Code Chart

Ratio, Letter

M20, A
M21, B
M22, C

 

[pgtr]

Is it safe to assume that I have an M-21 tranny? The car has been in my family for over 20 years and I guarantee it is stock

Hi Derrick and welcome

Saginaws were not used in 71 AFAIK. In 71 I believe there were two MT options -the M20 and M21. For a base engine it's likely an M20 which is the wide ratio Muncie. The M21 close ratio Muncie was typically found in LT1s for example. The ratios are:


1st 2nd 3rd 4th
M20 Wide 2.52 1.88 1.46 1.00
M21 Close 2.20 1.64 1.27 1.00

The M20 is a great transmission as is IMHO and works well with your L48 engine in stock or mod set up. I wouldn't change a thing with regard to the transmission other than addressing any service it may need. (engine is another story with plenty of opportunities).

You can order an assembly instruction manual specific to 1971 from most of the mail order parts places fairly reasonably. Also consider a 1971 (factory) Chassis Service Manual and maybe a 1971 (factory) Overhaul manual.

 

[pgtr]

Corvettes came with Muncie M-20, 21, and 22.

M22s were available in 1971?

Edit: Doh - nevermind - I see now in my book that '71 was the last year for M22s. It also looks like the powerteam options didn't permit anything but the M20 for the base engine that year.

 

[dshanks]

thanks for the great info

Thanks guys. Those are very detailed explanations. Unfortunately I had something come up last night so I couldnt get the car in the air. Just some info on the car and what I plan to do with it...
When I was a child, my dad always drove a Corvette as a daily driver. All vettes were between 1960 and 1974. My dad bought this car in the mid 80s and restored it to be a very nice original driver, and it appeared new. He then drove it every day for 10 years. After I left home at 20 the car was parked and didn't move much until he decided to sell it to buy a 1960, his favorite year (his 1st vette was a 60 fuelie). I objected, so either I bought it or it went, which was not acceptable to me. So here I am...
The car is still in great shape, a strong 10 footer. It has its rock chips here and there, but I dont mind. Its #s matching (except the color) according to dad, he didnt change a thing. Ive stored the rallys and replaced them with 18" chrome Bullitts that I had bought for a Typhoon that I dont own anymore. It still has a reliable but tired 350. Im in the process of pulling and crating the original motor for safe keeping. Im adding a 350/340 hp crate motor. In the process the tranny will be rebuilt, Bushings replaced, U-joints, the engine bay/underside/suspension painted, etc, etc. I dont want a show car or a race car, I want the same corvette I remember as a child, but refreshed a little. Someday, when I determine if the potential value of the car will be worth the work, I will return it to war bonnet yellow and build the original engine/carb and return the manifolds and AC etc.

Thanks again guys for all your help, Ill post again with the tranny #s ASAP.

 

[dshanks]

Guys, finally made it under my car...
P1M28A, so 8/28/71 M-20?

Is this a good tranny? What type of HP is it designed to handle? Is there a certain rearend gear that this car likely came with?

Thanks

 

[waterboy1976]

Derrick.....first of all welcome to CAC!!!!!...

M20...is a good Muncie....I have a nicely rebuilt M20 in my 73 coupe and we're pushing 420 hp and over 450lbs torque.......have it rebuilt by a good quality shop that was in business back then and still is today........Good luck