Originally Posted by Cruzzar
If I remember correctly, the drum portion has a residual check valve and the disk portions does not. If that is backwards, someone correct me. I'm not sure you can tell the differance between the two just by looking at the outside of the master cylinders.
You are exactly correct.
Drum masters have a 10 pound residual in both ports. The Disc brake master only has a residual in the front port (Rear Drum Circuit).
Drum masters have equal size "Bumps" on the lid, Disc Masters have a larger bump on the front, smaller on rear.
Dan @ Chockostang