M39 hydraulic brake master cylinder vent line connected to air pack: capping

[Robo McDuff]

M39 - M51A2. I am overhauling the hydraulic air-assisted brake system. The filler cap of the MC has a vent line connection going into the airpack where it joins another line going in. THat vent line irritates me when trying to bleed and fill the system or controlling the system. Can I just cap the connector on the airpack side, and use the MC filler cap connection for a remote second reservoir (or a free-hanging down-pointing vent line?

Unfortunately, the images of the airpack show 4-5 air line connections in front, but the schematic drawings in TM .. 20 do not show these extra lines, neither does it show the vent line of the MC.

Forgot to look where the second thick lines goes to; if its only the horn and wipers I will cap that whole thing, don't need then now.

 

[topo]

I caped the line when I added a easy to see reservoir to the master cylinder

 

[Robo McDuff]

You capped the connection at the airpack side as well?

 

[topo]

The tee in the top of the master cylinder has a vent line that goes forward to the fire wall and where the vent came off the top of the tee is where I plugged the line

 

[Robo McDuff]

Mine definitely went to the air pack



The air pack just after removing it from the truck. The image on right shows a close-up of the air regulator section. On top you see a connector that splits into a large pipe going to the front of the truck and a smaller connection sticking upwards. That is the connector to my MC vent line. Any idea how and why this is like this or is it something special for this truck.



The main air connector in front. If you look good, you see that the left wall has a bit of a dent in it. Happened during removal.

 

[Robo McDuff]

Here you see the vent line running up to the MC from the Airpack. The line is disconnected, you see the connector hanging free on the right.

 

[frank8003]

May be something in the PS archives to help you

 

[topo]

When my vent line was hooked up to the master cylinder I replaced the copper line with DOT nylon and left the nut on the fitting just hand tight . it was easer to get out of the way I had to wrap tape on it so the nut would not slide down .