The M30 transmission is a variation of the venerable 4L60E transmission, and is manufactured by General Motors. It has four forward gears, the third of which is a 30% overdrive. M30 itself is a RPO code. It stands for:
M30: TRANSMISSION, AUTO 4 SPD, HMD, 4L60E, ELECTRONIC
There is a different RPO code for every GM transmission, sometimes several. Here’s more on GM Transmission RPO codes.
The M30 transmission has an aluminum case and weighs 162 pounds with all the fluid in it. It has been made available in a wide variety of GM automobiles, from the Corvette all the way to the Silverado. There is sometimes an M30 stamp on the case, similar to the MD8 stamped on the 700R4.
You’ll find the 4L60E production code on the passenger side of the transmission by the pan toward the rear. It is a much more accurate way to identify any transmission. Even if you do happen to have M30 transmission, that is still very vague. What you need is to properly identify the 4L60E.
The easiest way to identify the M30 transmission is to look at the glove compartment tag. Each GM vehicle comes with one of these tags. It has all of the major RPO codes listed on it. These codes tell you everything from the paint that came on the vehicle, to the engine, and even the transmission. For instance, the LM7 engine is the 5.3L LS truck motor and the LR4 is the 4.8. You can’t tell them apart by looking at them, but the RPO code on the build sheet will tell you exactly what you are looking at.
The M30 transmission is compatible with any other 4L60E of the same year, but it is worth noting that GM changed a lot as far as how the clutches handled friction in the torque converter, what the torque converter was even made of, bellhousing bolt patterns, and more.