This page covers automatic trannies.
Go here for Chevy Manual Transmission Identification. The 4 cylinder models have 4 large cooling holes near the torque converter, while on the "bigger cars" there are no cooling holes. This is a 4 speed, overdrive unit. Generally used in straight and V6 and small block engines.
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Generally able to handle up to foot pounds of torque. It'll be marked THM on the bottom of the tailshaft housing.
The Turbo was modified to accept the Turbo driveshaft yoke. Used on large displacement, high torque engines and engines with towing packages. The 4L80E would be the "electronic" model.
Transmissions with a suffix of "C" on the end of the type THMC indicate the transmission has a lock up torque converter. Others have a tag rivited to the case.
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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: 19N Location of source serial number On the THM, 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 THMR4 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.
From 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.
Chevy Transmission Identification and Decoding. General Chevrolet Transmission Identification Transmissions are marked and identified by: - Casting numbers on the case, extention housing and side cover on manual trans.