If you're looking to replace or repair the transmission on your Chevrolet vehicle you'll first need to identify the model of transmission that you have. Chevy made several models of transmission for use in their vehicles and with a few glances at the parts you can identify exactly which model you own.
With the vehicle parked on flat ground and the parking brake fully engaged, crawl under the vehicle and take a look at the transmission pan. This will be bolted on below the transmission and should be easily viewable.
If the pan is shallow and almost perfectly square, the transmission is a THM700-R4 model.
If the pan is shallow and mostly square but has one of the rear corners missing, creating a diagonal instead of a corner, then the transmission is a THM350 model. However in some special cases this pan will have a "375-THM" stamped visibly on it. If you see this then the transmission is a THM375 model found in some full-size Chevy cars in the mid-70s.
If the pan is deeper and elongated with a piece of the pan towards the rear of the vehicle shallower than the rest it is a THM200-R4.
The final pan type you may encounter for automatic transmissions is also deep and elongated, but unlike the 200-R4 this one will have a uniform depth on the entire pan. This transmission model is the THM400 and was commonly found on most larger Chevy vehicles for the past several decades.
For a manual transmission you will need to look at the transmission housing and cover itself rather than any pan. Looking under the vehicle from the front will allow you to see the transmission cover with the housing extending behind it toward the rear of the vehicle.
If the cover has nine bolts on it, the transmission is a Borg Warner model.
If the cover has seven bolts on it look at the cover for a reverse-shift lever. This will be clearly visible if present as it will reside prominently on the front of the cover. If you see this lever, the transmission is a Saginaw model.
The only other model of manual transmission will also have seven bolts on the cover but the reverse-shift lever will not be visible on the cover. This transmission is the Muncie model, mostly used in heavier-duty applications.
