.

Identify Your Chevy Transmission

Automatic Transmission Identification & Description

Automatic transmission types are generally id'ed 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 & 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 tailshaft 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, cadilacs and large displacement engined, 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 & 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 rivited 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 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.




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

Chevy 4 speed automatic 700R4

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Powerglide

The 2-speed Powerglide was never installed by the factory into a G body. The Powerglide was discontinued by GM in the early 1970's.

It is still used by some drag racers to this day because of the relatively small amount of horsepower lost to the transmission.

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THM200/THM200C

Although the pan shape is very close to that of the THM350 family, a THM200/THM200C can be quickly identified by counting the pan bolts. A THM200/THM200C uses 11 pan bolts.

The C in THM200C denotes the use of a converter clutch (TCC) and will have a 4 cavity electrical connector on the driver side of the case. Many Oldsmobile G bodies were equipped with this transmission from the factory, yet it was often replaced with a THM350.

Additionally a THM200/THM200C pan will have the words "METRIC" and "HYDRAMATIC DIV." stamped into the bottom of the pan.

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THM250C/THM350/

THM350C/THM375B/M38

The THM350 was probably made in greater quantity than any other GM transmission. Irregardless of that, it was rarely installed in a G body. Typically, it was used in G body wagons. The light duty THM250C, or the even wimpier THM200C, was much more likely to be installed. Although those were often replaced at rebuild time with a 350 or 350C. All used the same pan, with 13 pan bolts, and are easy to misidentify.

For quick identification of the less desireable 250C, check the passenger side of the case, a 250C will have a band adjustement (looks like a stud with a locknut). All other transmissions in this family did not have this band adjustment.

The THM375B is a heavy-duty version of the 350 and can not be distinguished without disassembly or checking the transmission code.

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THM200-4R

The THM200-4R is the G body 4-speed automatic transmission, the overdrive installed in a G body from by the factory. It's most noticable feature is the the huge "boat" pan that extends virtually the entire length of the transmission case. This pan will also have the words "METRIC" and "HYDRAMATIC DIV." stamped into the bottom of the pan.

The THM200-4R is a derivative design of the THM200C with an overdrive section added and many other changes to improve reliability.

Like the "C" transmissions, the THM200-4R makes use of a converter clutch.

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THM375/THM400/M40 (THM3L80)

The THM400 was never installed in a G body by the factory.

It's most noticable pan feature is the "bulge" on the passenger side of the pan.

The THM375 is a lighter-duty version of the THM400 that used a 27 spline THM350 yoke.

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THM700R4/THM4L60/THM4L60E

The THM700R4 was never installed in a G body by the factory. Like the THM200-4R, it is also a 4-speed overdrive transmission that utilizes a converter clutch.

The THM4L60 was introduced in 1994 and is basicly a renamed THM700R4 with some minor changes.

The THM4L60E is a yet later electronically controlled version of the 4L60

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