OTHER  SIGNIFICANT  GTO  CODES
 
 
ENGINE I.D.
 
 
BORE & STROKE FIGURES

ENGINE
YEAR PRODUCED
BORE
STROKE
326
1963-67
3.781
3.750
350
1968-77
3.875
3.750
389
1959-66
4.063
3.750
400
1967-79
4.120
3.750
421
1961-66
4.094
4.000
428
1967-69
4.120
4.000
455
1970-76
4.150
4.210


         


 
V-8 FIRING ORDER
18436572
 
Counter Clockwise
Rotation
 

 




         
   
400, 428, 455 Engine ID


   
   

This is a quick block ID for junk yard hunting, etc. You must find the date code at the back LH side of the block first. The letter is the month, next 2 digits are the day and the last digit is the year. Here are 2 examples:

   
A249 code "XE"
A = January - 24 is the 24th day - and 9 is 1969
The block is a 69 428.

         Another example is:
K109 "WA"
K = October or November - 10th day - 9 = 1969
The block is a 70 455 4 bolt.
These motors usually have a large "70" at the rear of the block.
 
       


           Note - blocks with only 2 mounting holes or pads (for the motor mounts) per side is from 1969 and older blocks with 5 or 3 mounting holes or pads (for the motor mounts) per side is from 1970 and newer blocks with 2 freeze plugs per side is 1966 and older blocks with 3 freeze plugs per side is 1967 and newer certain blocks for 4 bbl carb usage have scallops in the cylinders at the deck for unshrouding the intake valves. Most 1967 and earlier blocks place these scallops at approx 4 o'clock and 8 o'clock while 1968 and newer blocks place the scallops at 3 o'clock and 6 o'clock. Early 2 bbl blocks and most newer blocks did not have any scallops.  
     
400
67 400 FULLSIZE: XA XB WA WB WM WN YA YB YC XV YD XU YU YV XC YE XW YF XX YX WD XT WE WY XY XZ YL XH XJ WF
67 GTO 400: XM XL WT WW YS XE WS WV YZ YI (RAM AIR) XS YR XP
67 FIREBIRD: WZ WU YT (RAM AIR) WQ XN WI
68 FULLSIZE: YA XA WA WB YC ZR YE YF XZ XH
68 GTO XM WT YS (400 HO) WS YZ (RA I) XS XP (RA II) WY XW
68 FIREBIRD: WZ YT (400 HO) WQ YW (RA I) WI XN (RA II) WU XT
69 FULLSIZE: WA WD YA YB WB WE YC YD XZ WX XH YF 69 GTO WT YS XM XX (RA III) WS YZ (RA IV) WW XP
69 FIREBIRD: WZ YT (RA III) WQ YW (RA III) WH XN
70 FULLSIZE: WE YD YB XZ WX XH
70 GTO & FIREBIRD: XX XV WT YS (RA III) WS YZ (RA IV) WW XP
71 FULLSIZE: WS XX YS
71 GTO, GP & FIREBIRD: XX WT WK YS
72 ALL: YX YZ ZX WS WK YS YT
73 ALL: YP ZK Y4 YX Y1 ZX YZ YT XK ZN WS YF WP Y6 YG YN ZS YY XX X5 Y3 YS XN
77-79 TA 6.6 (W72 opt.) Casting number 481988 XX is cast on the valley area and externally
   
428
67 WG YY YH Y2 XD WJ XK YK Y3
68 WG YH WJ YK
69 YL YH WG XK XE XJ WJ YK WF XF WL XG
   
455
70 FULLSIZE: YH - 2 BOLT WG XF - 4 BOLT
70 GTO: WA YA YC - 4 BOLT
71 FULLSIZE: WJ YC WG YG - 2 BOLT
71 OTHERS: HO (4 BOLT) WL WC YE
72 2 BOLT YH YC YA ZH
72 4 BOLT (HO) WM YB WD YE
73 YK X7 YD XM WW WT YC XE YA XL ZC ZA (SD) ZJ XD
74 Y9 Y4 Y6 A4 Z4 Z6 YY YU YX AU ZU ZX YW ZW YR (SD) W8 Y8
75 YW YU ZU ZW WX
76 Y3 Y4 Z3 Z4 Y8 ZB WX
   
 


             
Service Replacement (SR) blocks do not always have a code stamped on the front of the engine. They do, however, usually have a casting number. This casting number is usually on the RH side of the rear portion of the block - where the transmission bolts up. (See chart below.)

400 Castings
67 9786133
68 9790071
68 Ram Air 9792506
69 9790071
69 Ram Air IV 9792506
70 9799914
70 RA IV 9799915
71-74 481988
75 488986 (Early) 500557 (Late)
76 500557
77-79 568557
78-79 (TA 6.6) 481988 xx
   
428 Castings
67 9786135
68 & 69 9792968
   
455 Castings
70 9799140
71 483677 (Early) 485428 (Late)
72-74 485428
73 & 74 Super Duty 490132
75 & 76 500813
   
 
   
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HEAD ID's

 


 
YEAR APP. CASTING VALVES C.C. or C.R. NOTES
1967 400 2bbl/4bbi 061 2.11/1.77 75 Pressed in studs - Uuique open chamber
1967 400 4bbl RA I 97 2.11/1.77 72 Screw in studs - taller valve springs - D port
1967 400 4bbl RA I 997 2.11/1.77 72 Screw in studs - taller valve springs - D port
1967 326 2bbl 140 1.96/1.66 9.2 CR Pressed in studs - D port
1967 326 4bbl 141 1.96/1.66 10.5 CR Pressed in studs - D port
1967 400 2bbl 142 1.96/1.66 - Pressed in studs - Low compression - D port
1967 400 2bbl/4bbl 143 1.96/1.66 75 Pressed in studs - D port
1967 400 std, HO 670 2.11/1.77 72 Screw in studs - dual valve springs - D port
1968 400 2bbl 14 1.96/1.66 90 Pressed in studs - D port (B & G Body)
1968 400 2bbl/4bbl 15 1.96/1.66 75 Pressed in studs - D port (B & G Body)
1968/9 400 std, HO 16 2.11/1.77 72 Screw in studs - dual valve springs - D port
1968 350 2bbl 17 1.96/1.66 80 Pressed in studs - D port (A & F Body)
1968 350 4bbl, HO 18 1.96/1.66 68 Pressed in studs - D port (A & F Body)
1968 400 4bbl, RAI 31 2.11/1.77 72 Screw in studs - dual valve springs - D port (A & F Body)
1968/9 400 62 2.11/1.77 75/72 Screw in studs - dual valve springs - D port
1968 400 RAII 96 2.11/1.77 71 Screw in studs - dual valve springs - D port
1969 400 2bbl 45 1.96/1.66 8.6 CR Pressed in studs - Low Compression - D port (B & G Body)
1969 400/428 2bbl/4bbl 46 1.96/1.66 10 CR Pressed in studs - High Comp. - D port 30 or 45 seat angle (B & G Body)
1969 350 2bbl 47 1.96/1.66 80 Pressed in studs - D port (A & F Body)
1969 350 4bbl, HO 48 2.11/1.77 69? Screw in studs - dual valve springs - D port

1969

400 MT, RA, HO 48 2.11/1.77 72 D port RAIII
1969 400 RAIV 722 2.11/1.77 71 Screw in studs - dual valve springs - ROUND port
1970 350/400 2bbl 11 1.96/1.66 85 Pressed in studs - D port
1970 400 MT, RA 12 2.11/1.77 72 D port
1970 400 13 2.11/1.77 72 D port
1970 455 2bbl/4bbl 15 1.96/1.66 87 Pressed in studs - D port (B & G Body)
1970 400 2bbl/4bbl 16 1.96/1.66 10.1 CR Pressed in studs - D port
1970 455 HO 64 1.96/1.66 87 D port
1970 400 RAIV O-PORT 614 2.11/1.77 71 Screw in studs - dual valve springs
1971 455 66 2.11/1.77 114 Press in studs
1971 350 2bbl 94 1.96/1.66 90 Screw in studs - D port
1971 400 4bbl 96 2.11/1.77 96 Screw in studs - dual valve springs - D port
1971 455 2bbl 98 1.96/1.66 114 Screw in studs - D port
1971 400 2bbl 99 1.96/1.66 96 Screw in studs - D port
1971 455 HO O-PORT 197 2.11/1.77 111 Screw in studs- dual valve springs
1972 455 HO O-PORT 7F6 2.11/1.77 111 Screw in studs- dual valve springs
1972 350 2bbl 7H1 1.96/1.66 90 Pressed in studs - 45/45 degree seats
1972 400 2bbl 7J2 1.96/1.66 96 Pressed in studs - 45/45 degree seats
1972 400 4bbl 7K3 2.11/1.77 96 Screw in studs - dual valve springs - D port
1972 455 2bbl 7L4 1.96/1.66 112 Pressed in studs - 45/45 degree seats
1972 455 4bbl 7M5 2.11/1.77 114 -
1973/74 455 SD O-PORT 16 2.11/1.77 111 Screw in studs - dual valve springs
1973/74 350 46 1.96/1.66 96 Press in or screw in studs
1973/74 350 4C-5H 1.96/1.66 96 Press in or screw in studs
1973/74 400 4C-8H 1.96/1.66 98 Press in or screw in studs
1973/74 455 4X-1(H) 2.11/1.77 112/114 Press in or screw in studs
1973/74 400 4X-3(H) 2.11/1.77 98 Press in studs
1973/74 400 4X-4(H) 2.11/1.77 98 Press in studs
1973/74 400 4X-7(H) 2.11/1.77 98 Screw in studs - dual valve springs
1975 350 4bbl 5C-4 2.11/1.77 93 Press in studs
1975 350 5C-9 2.11/1.77 93 A.I.R.
1975 400 4bbl 5C-8 2.11/1.77 101 Screw in studs - 30/45 degree seats
1975 350/400 4bbl 5C-7 2.11/1.77 100 Press in studs
1975 455 5C-6 2.11/1.77 124 Press in studs
1975/76 455 4bbl 51 2.11/1.77 124 Screw in studs - 30/45 degree seats
1975/76 455 4bbl 6H 2.11/1.77 124 Screw in studs - 30/45 degree seats
1975/76 350 6S-9 2.11/1.77 93 -
1975/76 400 6S-7 2.11/1.77 100 -
1975/76 455 6S-6 2.11/1.77 124 -
1975/79 350/400 6X-4 2.11/1.77 98 Screw in studs - dual valve springs - D port
1975-79 400/455 6X-8 2.11/1.77 101 Screw in studs - dual valve springs - D port
           

     
 
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GM Transmission Identification & Decoding
 
     
 

Transmissions are marked and identified by:

Casting numbers on the case, extension housing and side cover (on manual trans).
Date Casting Codes
Assembly Date Code Stamping - can be stamped anywhere...
Chassis Vin Number stamping - beginning in 1962

Transmissions are also expressed via the RPO number, usually beginning with "M".

Automatic Transmission Identification and Description

Automatic transmission types are generally identified by their pan shape.

 
     
 
 
     
 

The THM200 and the THM250 have pans shaped like a THM350, HOWEVER, the THM200 will have the words HYDRAMATIC DIV. and METRIC stamped into the pan.


Automatic Transmission Description and Usage

THM200 - Light duty, "metric" 3 speed transmission.

THM250 - Used in small 4 cylinder cars (Vega, Sunbird, Monza) from 1973 to 1981 and some Nova/Camaro/Chevelle 6 cylinders in 1974 & 75. The 4 cylinder models have 4 large cooling holes near the torque converter, while on the "bigger cars" there are no cooling holes.

THM200-R4 - Used in GM rear wheel drive cars with the 3.8 V6, 305 & 350 Olds and 301 Pontiac from 1981 to 1989. This is a 4 speed, overdrive unit.

THM350 - Medium duty 3 speed trans used from 1969 to 1989, Used in Buick, Olds, Pontiac and Chevrolet cars and Chevy & GMC light trucks until 1987. Generally used in straight and V6 and small block engines. Generally able to handle up to 400 foot pounds of torque.

THM375B - This trans is identical to the THM350, but is considered a heavier duty transmission.

THM375 - This transmission is a derivative of the THM400 sharing the external appearance of the 400. It'll be marked 375-THM on the bottom of the tail shaft housing. It's a light duty version of the THM400, has ABSOLUTELY NO RELATION to the THM375B, and was found in 1972 to 1976 full-size cars. The Turbo 375 was modified to accept the Turbo 350 driveshaft yoke.

THM400 - The THM400 was GM's Heavy-duty 3 speed transmission used from 1964 to 1990. Used on large displacement, high torque engines and engines with towing packages. Generally found in Chevy & GM trucks, Cadillac’s and large displacement engine, full size GM rear wheel drive cars.

THM700-R4 - 4 Speed transmission used in GM cars and light trucks with the 2.8, 3.1, 4.3, V6, Chevrolet built 305, 350 and 454 engines from 1982 to 1992.

4L60 - Early 1990's saw the 700R4 renamed to the 4L60, and "electronic" models were named 4L60E. 4L60 means 4 forward speeds, L = longitudily mounted (rear wheel drive). 60 is the strength rating (less than the 4L80).

3L80 - The 3L80 is a renamed THM400, used in the early 1990's. The 3L80HD would be the THM475 (heavy duty unit).

4L80 - An overdrive model of the THM400. The 4L80E would be the "electronic" model.

Transmissions with a suffix of "C" on the end of the type (THM200C) indicate the transmission has a lock up torque converter.



Automatic Transmission Identification and Decoding

Specific methods of identification are as follows (and yes, this section needs to be rewritten).... Some transmissions have a code stamped onto them. Others have a tag riveted to the case.

Most transmissions will have a "source serial number" (chassis vin) usually found close to the transmission code. This number will contain division ID #, model year, assembly plant and production sequence (last 6 digits) of the VIN stamped onto the transmission. Example: 19N500001. The source serial number is from the CAR the transmission originally went into, NOT the assembly plant.



Location of source serial number

On the THM350, the VIN will be stamped on either the drivers side housing near the shifter, on the right side of the housing just above the pan, or on a boss behind the bell housing flange on the passenger side of the transmission.

On the THM400 the VIN is stamped on a machined surface just above the pan on the drivers side.

On the THM200-R4 the VIN is stamped onto the housing towards the rear of the pan, on the drivers side.

On the THM700-R4 the VIN is either stamped onto a boss behind the bell housing flange on the passenger side, just above the pan on the drivers side, or just behind the governor cover, stamped vertically where the case meets the tail shaft housing.

Prior to 1967, transmission ID numbers contained the plant prefix code, month and date of production (expressed numerically) and a shift code (D = Day, N = Night). From 1967 on, the ID number contained the transmission type or plant prefix, Date (coded below) and a shift code. The constants in decoding the trans ID number are the date the transmission was produced.

Pre-67 Example: C213N - (C = Cleveland Powerglide, February 13, Night Shift)
Post-67 Example: P9E03 - (P = TYPE, 9 = year (1969), E = Month, 03 = Day of Month)

Month code: (NOTICE this is NOT in alphabetic order)
A = Jan, B = Feb, C = Mar, D = Apr, E = May, H = Jun, K = Jul, M = Aug, P = Sep, R = Oct, S = Nov, T = Dec

 
     
     
     
  Manual Transmission Identification & Description  
     
 
Manual Transmission Eyeballing
 
     
 
 
     
 

Muncie (left) Saginaw (center) Borg Warner (right)

 
 


To quickly finger what you have, notice in the above picture:

The Muncie reverse lever is in the extension housing, and the cover has 7 bolts.
The Saginaw reverse shift lever is on the cover, and the cover has 7 bolts.
The Borg Warner has a 9 bolt cover.
Muncie’s are the hot tip, since they usually were used with high performance engines. Again on the Muncie, and looking at the cover, 3rd/4th gear lever is on the left. 1st/2nd gear lever is on the right.

Further Muncie identification
3 Muncie 4 speeds were offered. The M-20 wide ratio, the M-21 close ratio, and the "Extra heavy duty close ratio" M-22, also known as the "Rock Crusher". The M-22 was generally installed behind severely powerful (high torque) big-block engines. The M-22 is distinguished from an M-21 by the angle of the gear teeth. The M-22 has "straight cut" gears. Due to this, the box tends to be nosier (whines or howls almost like a blower, which is why it's called a "rock crusher") than other boxes. The M-21 has a higher pitch angle on its gear teeth.

The close ratio gearboxes generally came with 3.73+ gear ratio'ed cars. 3.55 geared and higher (numerically lower) cars used the wide ratio gearbox.

Due to the wide combination of id's, stampings, numbers, etc... varied and even GM couldn't keep track of what was what, it's best to ID your gearbox visually, taking what is stamped on the box FWIW. The best way to ID the transmission is to count teeth.

 
     

 
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Muncie 4 speed spline, groove and tooth count characteristics.
   
     
 
Type/Year
Input Spline
Input Groove
Input Gear
Tooth Count
Cluster Gear
Tooth Count
Output Spline
Gear Ratio
M20: 1963 - 65
10
none
24
29-22-19-17
17
note 1
M20: 1966 - 70
10
2
21
25-22-19-17
27
note 2
M20: 1971 - 74
26
2
21
25-22-19-17
32
note 2
M21: 1963 - 70
10
1
26
27-22-19-17
27
note 3
M21: 1971 - 74
26
1
26
27-22-19-17
32
note 3
M22: 1965 - 70
10
none
26
27-22-19-17
27
note 3
M22: 1971 - 72
26
none
26
27-22-19-17
32
note 3
 

 

Note 1: M-20 gear ratio: 1st 2.56:1, 2nd 1.91:1, 3rd 1.48:1, 4th direct
Note 2: M-20 gear ratio: 1st 2.52:1, 2nd 1.88:1, 3rd 1.46:1, 4th direct, Rev 2.59:1.
Note 3: M-21/22 gear ratio: 1st 2.20:1, 2nd 1.64:1, 3rd 1.28:1, 4th direct, Rev 2.27:1

 



  Effective: October 21, 1968, an additional letter was added to the plant prefix number to help identify the gear ratios in Muncie transmissions. The additional letter codes as follows:  
     
 
Muncie 3 speed Manual
Muncie 4 speed manual transmissions
Suffix
1st gear ratio
Suffix
1st gear ratio
A
3.03:1
A
2.52:1 wide range
B
2.42:1
B
2.20:1 close range
C
2.20:1 Rock Crusher
 


 
Of course like engines, transmissions come and go over time, so below is the (as complete as I can make it) transmission plant prefix list:
   
     
 
Plant
Type
Prefix
Plant
Type
Prefix
Cleveland
Manual Powerglide
A
Saginaw
overdrive
O
Cleveland
Turbo Hydramatic
B
Warner Gear
3 & 4 speed
P
Cleveland
owerglide
C
Muncie
4 speed
P
Hydramatic
Turbo Hydramatic
CA
Muncie
4 speed
R
Saginaw
Overdrive
D
Saginaw
4 speed
R
McKinnon
Powerglide
E
Muncie
3 speed
S
Muncie
3 speed
H
Saginaw
3 speed
S
McKinnon
3 speed
K
Toledo
Powerglide
T
GM of Canada
Turbo Hydramatic
L
Cleveland
Turbo Hydramatic
X
Muncie
3 speed and Overdrive
M
Toledo
Turbo Hydramatic
Y
Muncie
4 speed
N
 





 
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