1973 Master Cylinder Mystery

[Father&son56project]

MJN: Thanks for that pic out of the parts catalogue! I looked up those numbers and there are readily available master cylinders that claim to interchange with those numbers. Curiously though, they all have the 1.125 inch bore and a shallow brake rod dimple (which is exactly what various brake companies say not to use with manual brakes). After seeing your reply I got curious and took a closer look at the MC on my son’s truck. While it was pretty cruddy, I managed to get it cleaned up and flushed out in order to give it a try. I also looked carefully at it, and it has a 1 inch bore (as is recommended for manual brakes) AND a shallow dimple (as is not recommended for manual brakes). Mind you, god only knows if this is the correct MC so I’m not basing any decisions on it. I got awful close to being able to test it, then discovered that the front drivers flex hose was plugged so I couldn't finish bleeding the brakes. If I do decide to change it, I will probably just get one meant for a ‘74.

Thanks for the help!