* Check the VIN: The Vehicle Identification Number (VIN) contains a code that indicates the transmission. You can find the VIN on the driver's side dashboard, usually visible through the windshield. You'll need to look up the decoding for the specific code on a Chevrolet VIN decoder (many websites offer this service). This is the most reliable method.
* Look at the Transmission Case: The transmission case itself usually has a tag or casting number. This number can be cross-referenced with parts catalogs or online databases to identify the transmission type (e.g., TH350, 700R4, SM465). You may need to get under the truck to see it clearly. The tag might be difficult to read depending on the condition.
* Look at the Shifter: The shifter pattern (PRNDL or PRND2L) gives you a clue, but isn't definitive. Different transmissions can share similar shift patterns.
* Check the Owner's Manual (if available): If you have the original owner's manual, it should specify the transmission type.
* Check Build Sheet (if available): Sometimes a build sheet is available, which details the truck's specifications, including the transmission.
Important Note: 1989 Chevy trucks could have a variety of transmissions depending on engine size, trim level, and options. Common transmissions included the 3-speed automatic TH350, 4-speed automatic 700R4, and various manual transmissions (e.g., SM465, Saginaw 4-speed). You will need to use a combination of the above methods for the most accurate identification.
