How the brake works?

[engele]

Hi guys,

i have some questions about the US brake cylinders. It´s different to the German ones.
I have a M1078A1 and a M923. Why they have 3 lines to the cylinder? Attached the pics of my LMTV.
1 for parking brake?
1 for service brake?
1 asa a vent line?

and can someone explain me the two parts where the lines go on? I have found a diagram but it´s a little difficult for me.
I have to install test connections to measure the pressure for the service brakes for each axle. I will use the synflex lines for them. It´s the easiest way because the european connections are metric.

Best regards Alex

 

[Oxyacetylene]

You are correct about what the lines are for. The innermost line in your photo, the vent line, can be traced upwards to an open port on the frame rail on each side. When you press or release the service brakes (brake pedal) that vent line lets the service chamber side expel or suck in air as the diaphragm moves. Line 1 is to apply the service brakes. Line 2 releases the parking brakes. Viewing those rear brake chambers as a whole, the service brake portion is inside (closer to the wheel) and the parking brake section is outside. There are a few diagrams online that explain how the rear chambers function for air brake systems. These trucks use wedge brakes, but the operation of the air chambers themselves are the same, as far as I know.