KJLVette

I am trying to understand what transmission is in my car. I have read many threads regarding M21, M22 - Muncie, Borg Warner, RockCrusher, etc.. and am now curious what Transmission I have in my 63. The only numbers that I could identify are as follows: 3851325 and US Patent 3088336 General Motors Corp.
I have the Corvette Blackbook - but do not see anywhere in the book where they list Transmission numbers? Am I overlooking something or isn't the transmission considered an item when you talk about having a numbers matching car ( not that I care too much about that as mine is a driver - 1971 350, Holley 650, Hurst shifter)
Thanks for any feedback you can provide :)
Kevin

JohnZ

3851325 is a '64-'65 Muncie main case; should also have a 3846429 tailshaft housing and a 3831707 side cover with studs and nuts attaching the shift levers. There's no way to tell whether it's an M20 or an M21 without pulling the side cover and counting the input shaft gear teeth; 24 teeth is an M20, 21 teeth is an M21. There should be two sets of numbers stamped (not cast) on the vertical flange on the rear of the main case on the passenger side where the tailshaft and bearing carrier bolt to the main case - one will start with a "P" followed by four numbers, and the other will be a 9-digit partial VIN which will show what it was originally installed in, what model year, kind of car, and the assembly plant.

KJLVette

JohnZ,

Thanks for the AWESOME reply :) I have always loved Corvettes since being a kid, and am so happy and proud to own mine now. I look forward to contributing and passing along the valuable information that I come across in the years to come to others. All of the commentary and comradery on this forum has helped me really appreciate and enjoy my Vette more and more - You just can't put a price on that :cool:
Thanks
Kevin
God Bless America and the Freedom we share :cheers:

bamavettes

There is a way to tell if you have a M20 or M21. You can give it the test. This was given to me a few months back by a forum member. I would give him credit if I remembered his name. It does work.


Drive your car in 4th gear at exactly 2000 RPM's. Downshift to 3rd maintaining the exact same speed. Keep your pedal foot steady. If it goes to 2500 RPM's you have the M21 and if it goes to 2800 RPM's you have the M20.

Let us know what you find out.

396 RAT

Good tip on the 4th to 3rd gear RPM indicator.
You would know it if you had an M22, Gear whine
and a true drain plug. (the lower casting boss is drilled and tapped in
addition to the normal upper fill plug)
M-20 wide ratio has a lower 1st gear (easiest way to tell)
The M-20 close ratio turned into the M-21 in 1966 those 2 and the M-22
share the same ratio's.
Kind of confusing:crazy:
63-65 M20's were either Wide or Close ratio. Then in 66 the M-20 close
ratio turned into the M-21. (Just a designation change, to make it easy)
As I recall most mid yrs had the close ratio with the 2.20:1 1st gear
V.S the Wide ratios 2.54:1 (early 63) 2:56:1 from mid 63 to much later. :lol:
I am not an expert, but have owned (2) 65's that both had the close ratio
M-20.
Let us know what you have? :cheers:

KJLVette

BammaVettes / 396RAT,
Again - Many Thanks for the information :) I will perform the test you've specified and reply back with the results :yesnod: Please be patient with my response as I live in Cleveland, OH and they are already calling for some winter weather this weekend :U However, you have just given me another excellent reason to take her out for another burn :jester My education process continues :cheers:
Thanks
Kevin

KJLVette

Well, we didn't get any accumulation of snow and the road crews didn't dump salt all over the place :D The results of your (Bamavettes) test are as follows: In 4th at 2000 Rpm's, I downshifted to 3rd the Tach jumped to about 3300, then as I kept the speed steady in 3rd (about 47 mph) the Tach leveled and held at 2500 Rpm's, therefore I assume that I have the close ratio M-21
396RAT, I assume from your last post that your M-20 close ratio is the same as the M-21 that's in mine 63? Does that sound right?
Thanks for the help - it was fun to do the test :cool:
Kevin

396 RAT

Sounds like you have a close ratio M-20, but everyone calls 'em
M-21's. If your tranny is 63-65 its a M-20, 66 or later Its an M-21.
(They are about the same thing, They just re-designated the
close ratio M-20 to M-21 in 1966.)
I love that ratio! I have the same ratio in a 65 Top Loader
as well as my Vette.
1st gear can actually get used! With tall RR gears the wide ratio can
make 1st seem like a granny gear.
Too bad about the Salt! Better park that beauty and let
the winter projects begin!