How to Identify a M22 Rock Crusher

by Janos Gal
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An M-22 "Rock Crusher" is a Muncie four-speed transmission for cars made by General Motors in the 1960s. Identify a transmission type correctly before fitting it into your car. If you have the incorrect transmission, your car may not function properly. You can identify several unique signs that identify an M-22 "Rock Crusher," even if it does not have a GM hallmark imprinted on its surface.

Step 1

Check the casting number, the production year and the gear ratios on the aluminum serial number plate attached to the transmission box. Every GM Rock Crusher has a casting number with which you can easily identify a transmission box.

Step 2

Count the input shaft teeth to find out the make of the transmission. Input shafts differ in each GM transmission, so you can easily identify an M-22 "Rock Crusher by its input shaft count. Each transmission has different numbers of teeth. An M-22 "Rock Crusher" always has 26 teeth.

Step 3

Count the number of splines in the transmission. M-22 "Rock Crushers" made between 1967 and 1970 have 10 splines; transmissions made between 1969 and 1974 have 26 splines.

Step 4

Look for the "GM" sign imprinted on the transmission box to identify the manufacturer of the transmission.

Step 5

Check whether there are any rings around the shaft splines. An M-22 "Rock Crusher" has no rings, so if you see rings in your transmission, it means it is not an M-22 "Rock Crusher."

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