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Transmission Identification & Decoding
General Transmission Identification
Transmissions can be identified in the following manner:
Casting numbers : Located on the case, extension housing
and side cover (manual).
Automatic Transmission Identification and Description
Their pan shape generally identifies automatic transmission types.
Automatic Transmission Description & Usage
THM250 - Used in small 4 cylinder cars from 1973 to 1981 and some 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 from 1981 to 1989. This is a 4 speed, overdrive unit.
THM350 - Medium duty 3-speed transmission used from 1969 to 1989. It was generally used in straight and V6 and small block engines, and generally able to handle up to 400 foot pounds of torque.
THM400 - The THM400 was GM's Heavy-duty 3-speed transmission used from 1964 to 1990. It was used on large displacement, high torque engines and with towing packages.
THM700-R4 - 4 Speed transmission used in GM cars and light trucks with the 2.8, 3.1, 4.3, V6, and Chevrolet built 305, 350 and 454 engines from 1982 to 1992.
Automatic Transmission Identification and Decoding
Some transmissions have a code stamped onto them while others have a tag riveted to the case.
For all you "numbers matching" types out there, most transmissions will have a "source serial number" (chassis VIN) usually found close to the transmission code. This number will include the division ID #, model year, and the assembly plant and production sequence (last 6 digits) of the VIN stamped onto the transmission. An example would be 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 bellhousing 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 bellhousing 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 tailshaft housing.
Before 1967, transmission ID numbers contained the plant prefix code, month and date of production (expressed numerically) and a shift code (D = Day, N = Night). After 1967, the ID number contained the transmission type or plant prefix, Date (coded below) and a shift code.
Pre-67 Example: C213N - (C = Cleveland Powerglide, February 13, Night Shift)
Manual Transmission Identification & Description
The Muncie reverse lever is in the extension housing, and the cover has
The M-20 Cluster gear teeth are 25-22-19-17. The Input shaft/gear teeth: 21.
Note, remember that transmission pans can be changed easily, so you should avoid relying upon them directly for a code if possible.
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Ich mochte was Sie denken wissen. Sie konnen mit mir sprechen heir. Mein Deutsch is nicht sehr gut. Ich mag English bitte.
10/12/99 04:46 PM