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GM Transmission Identification

Need Help with Transmission Identification?

As time marches on, technology changes. Classic car restoration is not a new hobby, and the older the project car, the more likely it is that someone has installed a different transmission at some point along the way. Modern 6-speeds (above) are easy to spot, and 5-speeds are not difficult either, but when it comes to older 4-speeds and automatics, the increased variety can muddy the waters. So, whether you are heading out to check out a "For Sale" ad that could be your next project or trying to make heads or tails of a junkyard find, the following charts can be useful guides when it comes to transmission identification.

Automatic Transmission Identification:

The easiest method of GM automatic transmission identification is to examine the pan. New transmission designs came with new, unique pan shapes, and the general shape of the pan often paints a fairly clear picture of which automatic transmission you are dealing with. Once you identify the pan, count the number of transmission pan bolts for confirmation.

14 Bolts 16 Bolts 11 Bolts
13 Bolts 13 Bolts 16 Bolts
  17 Bolts  
   

Manual Transmission Identification:

As mentioned above, modern 5-speed and 6-speed manual transmissions are easy to identify, but older 4-speed transmissions have more variety. While there are no distinctive pans and bolt counts to make transmission identification simple, 4-speed manual transmissions can be generally identified by examining the side profile. The shape of the main housing will give a reasonably reliable indication of the transmission group to which your gearbox belongs. Unfortunately, this makes transmission identification difficult to accomplish while the gearbox is installed in the vehicle.


For more useful diagrams and helpful restoration tips, check out https://news.classicindustries.com/category/diagrams/