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Hello
I have a 68 C 3 with 427 engine and 4 speed Muncie Trans.
Casting # GM3885010
Serial # P0920
Can somebody tell me if its a 20, 21 or 22 transmission?
Is this close ratio ? What ratios do the gears have?
Thank you for help.
Best regards from germany
Jürgen
Which engine do you have? Do you know the rear axle ratio? The table below from the pdf above shows some possibilities. There's no difference or mystique between the M20 and M21, they just have different gearing to optimize engine output in combination with the installed rear axle ratio. An M22 is possible but I don't have the info at my fingertips on what 427s and axles would pair with it.
The code number identifies the source, model year, month and day produced. The Muncie heavy duty (aluminum case) passenger transmission is stamped vertically on the passenger's side of the case just ahead of the extension. The first letter will be P for Muncie, H.D. 4-speed, Aluminum Case. (This is heavy duty in relation to an aluminum passenger car transmission and is not to be mistaken for the M22.) The next number will be the last digit of the model (not calendar) year (8 or 9). A letter will designate the month produced (see chart). Two digits will be the day of the month. A suffix letter will end the code (see chart).
Example: P8E03A
(P)
Muncie HD 4-speed day
(8) )
1968 model year
(E)
month-May
(03)
Day
(A)
A suffix=wide range
Production months are designated as follows:
A January
B February
C March
D April
E May
H June
K July
M August
P September
R October
S November
T December
Muncie 4-speed Passenger (Aluminum Case): Suffix First Gear Ratio
A 2.52:1 - wide range M20
B 2.20:1 - close range M21
C 2.20:1 – “Rock Crusher” M22
Transmissions built at Chevrolet plants will carry a production code number. The same VIN stamp that is used on the engine block is used on the transmission in the same area as the production code number.
Since your production number P0920 and no VIN stamp would indicate it is not the original trans for you car.
Thanks for the infos
i also think now thats not the original trans.
I have a L68 /400 Hp and axle ratio 3.55 HD Positraction # 1AZ91867
What i could find out now is following
input shaft 10 spline with 2 rings. outputshaft 27 spline, countershaft 1 inch
1st gear 36 teeth, on countershaft 17 teeth, but this will be a 2.12 ratio.
I am a little bit confused now. for the ratio.
Was a Muncie with this ratio available?
Best regards
Jürgen
A last question,
do all original trans have the vin # of the car stamped in ?
My convertible was produced October 1967,
Thanks for all the infos.
Regards
Jürgen
Yes yours should have the VIN stamp. The reason I said should in Corvette production nothing is 100%. But your date stamp on your trans also indicates it is not produced in 1968. I think VIN stamping goes back to 1962.
Muncie Identification
