The new combination brake pump has two connections:
A) M12x1.00 thread for the pump from the handlebars (e.g. thumb brake pump)
B) M10x1.00 thread for the cable that goes to the rear brake calliper
How does that work then?
Simply so that the pump can be operated on the handlebars as long as the combined brake pump is not depressed.
The pressure is fed through the combined brake pump directly to the rear brake calliper.
If the handlebar pump is pressed, the combined brake pump can also be actuated. In principle, the two pumps are arranged in series. If the combined brake pump is pressed, you can press the pump on the handlebars as much as you like. Nothing happens because the input (M12x1.00) is "closed" by the piston in the combined brake pump.
The combi brake pump for the rear brake was developed so that both a pump on the handlebars (thumb or pull brake does not matter) can be used together with the foot brake for the rear wheel. This is often required by the regulations. In this case, the foot brake must remain in place. However, an additional brake pump operated by hand is permitted.
