If the sticker is missing or illegible, you can try these less reliable methods:
* Check the owner's manual: If you still have the original owner's manual, it should specify the transmission type.
* Look at the transmission itself: This is difficult and requires some mechanical knowledge. You'd need to locate the transmission and look for a tag or casting number on it. You would then need to cross-reference that number with a parts catalog or online database, which can be challenging.
* Count the gear selector positions: While this *might* seem helpful, it's unreliable. Both 3-speed and 4-speed automatics in that era typically had the same number of gear selector positions (Park, Reverse, Neutral, Drive, Low/1, sometimes Overdrive/2). The "Low/1" and "Overdrive/2" positions aren't definitive indicators of a 3 or 4 speed transmission.
The door jamb sticker is the most reliable and easiest method.