What size?
IIRC, 3100 and 3600 on up were different animals.
On the 3600 and larger, there is a rod that goes back behind the MC, connects to a pivoting crosspiece, which is connected to the MC plunger.
You stomp on the brakes, the rod moves forward, the crosspiece pivots, which drives the plunger in.
I don't have a camera handy right now, otherwise I'd take a picture.
