The Saginaw four speed transmission is a transmission that was used in a variety of GM cars in the 60’s. They were popular in the Muscle Car era. As a rule of thumb, they were not built to handle the kind of power that a Muncie transmission could handle. So, if you are looking to drop one in a vehicle that makes more power than it did when it was stock, you should consider going a different way. That being said, you didn’t come here for my opinion about what to do with a transmission you could be very well looking at right now. Lets get straight to it!
Saginaw vs. Muncie identification
Far and away the easiest way of telling them apart is what the transmission is made of. The Saginaw was made out of iron. It usually found its way into trucks and other heavy vehicles where weight was not at a premium. The Muncie was made out of Aluminum. So and old Muncie will usually be smooth and a little greasy. An older Saginaw will usually be coated in rust unless it was cared for extra ordinarily well. There is quite a difference between them side by side. Have a look:
A lot of people just need to know which one is which, and the case material will provide you with fine answer to that question.
Another way to tell the identify a Saginaw transmission is to look at the shift arms. On the Muncie they are on the tail shaft, whereas with the Saginaw they are on the side of the case. Observe the picture above. You can see the shift arms right on the side of the case.
Saginaw four speed transmission identification codes
Also, one of the most common issues you may experience when looking at a Saginaw is whether or not you are even looking at a three speed or four speed version of the transmission. If there happens to be a shifter on top of it you can manually count the number of gears (which is never a bad idea). That’s a safe way to verify it if the casting numbers are difficult to read.
You’ll find the casting numbers on the main transmission case just after the tail shaft housing. The first letter in this number is going to tell you exactly which Saginaw transmission you have. You are looking of the letter R. If the first letter of the code starts with an R than you can be confident that you have found what you can be confident that it is a four speed version.
If it starts with an M you are looking at a Muncie, and if starts with an S you are looking at the 3 speed Saginaw. If you would like to read more about decoding a 1960’s transmission, this page is pretty good.
Saginaw 4 speed identification- figuring out the gearing
I’m not a big restoration guy. I don’t look for numbers matching pieces for my vehicles. So this way is going to help you narrow down exactly what kind of saginaw that you may have.
Count the rings: There are rings around the input shaft that will help you determine the gearing in the transmission itself. According to camaros.net, they are as follows:
- No lines on the input shaft- First 2.84, Second 2.01, Third 1.34, Fourth, 1.00
- 1 Line- First 2.54, Second 1.84, Third 1.44, Fourth, 1.00
- 1 Line- First 2.54, Second 1.84, Third 1.32, Fourth, 1.00 <— Much less common
- 2 Line- First 3.11, Second 2.20, Third 1.47, Fourth, 1.00
- 3 Line- First 3.50, Second 2.46, Third 1.65, Fourth, 1.00
Good luck with your project, and thank you for reading.