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ID a Muncie

 

The Muncie 4-speed transmission was used with many different GM models and engine combinations from 1963 through 1974.

The main difference between the Muncie and the Borg-Warner is that the Muncie has a 7-bolt side cover and the Borg Warner

has a 9-bolt side cover. 

 

Muncie 4-speeds were produced in two different ratios wide ratio (M-20) and close-ratio (M-21).

An extra heavy duty close-ratio version (M-22) was also offered on many of the big-block high-performance models.

The choice of transmission was dictated by the engine size and rear-axle ratio. Axle ratios of 3.73 and lower (numerically higher)

came with close-ratio transmissions, while axle ratios of 3.55 and higher (numerically lower) used wide-ratio transmissions.

In addition, many GM high-performance engines came with M-22 “Rock-Crusher” in the 1970-73 years, however an early

version of the M-22 was available as early as 1965 in Corvettes. 

 

The main internal differences in the 3 types of transmissions are listed in the parts below.
• M-20 differs from M-21: Input shaft and Cluster gear
• M-20 & M-21 differ from M-22: Input shaft, Cluster gear, First, Second, Third, Reverse idler gear.

All other components interchange, with the exception of production upgrades and changes.

 

For example, 1963-65 synchronizers, blocking rings, etc. do not interchange with 1966 and newer

versions, and therefore the transmission must be stock or interchanged as a unit.

 
 

 

                            1970 Information

 

Casting: 3925660  Years: 1968 - 1970  Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st

Casting: 3925661  Years: 1970 - 1974  Ratios: M20 2.52 1st , M21 2.20 1st, M22 2.20 1st

 

Ratios:

Year 1966-1974    Type: M20   Rings: Two    Ratio: 2.52 / 1.88 / 1.46 / 1.00 / 3.11

Year 1963-1974    Type: M21   Rings: One    Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27

Year 1967-1974    Type: M22   Rings: None   Ratio: 2.20 / 1.64 / 1.28 / 1.00 / 2.27

 

Reading Serial & VIN Numbers

 

Example 170N553721 P0E08C

1= Norwood Assembly Plant, unit #1

70 = 1970

N = Norwood

553721 = the last 6 digits of your VIN

P = Muncie

0 = 1970

E = May

08 = day

C = M22 (A=M20, B=M21, C=M22)

 

 

Date Codes: 

 

A = January, B = February, C = March, D = April, E = May, H = June
K = July, M = August, P = September, R = October, S = November, T = December

 

  Main Case
3831704 1963 Only small 6207NR Front Bearing ,Pat. Pending, 7/8" Bore
3839606 1963 - 1964 Regular Bearing Pat. Pending, 7/8" Bore
3851325 1964 - 1965 7/8" Bore Patent Pending Mostly 1964
3851325 1964 - 1965 7/8" Bore Patent Number
3864848 1965 7/8" Bore Patent Number
3864___ 1965 Milled off last 3 digits 7/8" Bore Patent Number
3885010 1966 - 1967 1" Bore Patent Number
3925660 1968 - 1970 1" Bore Patent Number
3925661 1970 - 1974 (some early 1975 cars) 1" Bore Patent Number
   
  Tailhousing
3831731 1963 Thin Fin Tail Driver speedo 27 spline
3846429 1963 Thin Fin Tail Driver speedo 27 spline
3846429 1963 - 1965 Regular thick web, driver speedo, 27 spline
9779246 1964 - 1965 Pontiac Catalina Long Tail Driver Speedo 27 Spline
3857584 1966 - 1970 Passenger side speedo, 27 spline
3978764 1970 - 1974 passenger speedo, 32 spline output
   
  Side Cover
3831707 1963 - 1965 Early side cover stud type shift shafts
3884685 Cover issued with "584" tail stud type shift shafts
3950306 Short boss with bolt on type shift shafts - no switches
3952642 Long boss bolt on type w/ TCS switch on 3-4
3952648 Short boss bolt on type w/ TCS switch on 3-4
335308 Long boss bolt on type with neutral safety switch. Some have a boss for the switch that is cast but not machined on 1-2.