Differential Vent and Tag Axle Brakes

[tropical36]

'm under the rig today to check on the differential vent to make sure it clear and not clogged in any way, but didn't find such a thing.

While I'm looking around, I notice that the tag axle has it's own master cylinder, which I checked and filled as it was super low. Last summer, I had the brake fluid changed by professionals after boiling the stuff coming down the big horn mountains. I was told that even though, the tag drum brakes had not been removed for a visual inspection, the fluid was getting back there. So, it seems obvious to me that they didn't check this master cylinder and/or lost a lot of the fluid in there. So much for pros.
Here's what the whole thing looks like. There is a controller of sorts that is actuated by the main brake fluid line. This in turns supply's a large air or vacuum cannister which has said master cylinder attached to it. This master cylinder in turn, supply's the two wheel cylinders on the tag axle.
Is anyone familiar with this setup, or have had any experiences with it?
Also, any ideas on this elusive vent for a Dana axle differential, that I can't find.

[tropical36]

'm under the rig today to check on the differential vent to make sure it clear and not clogged in any way, but didn't find such a thing.

While I'm looking around, I notice that the tag axle has it's own master cylinder, which I checked and filled as it was super low. Last summer, I had the brake fluid changed by professionals after boiling the stuff coming down the big horn mountains. I was told that even though, the tag drum brakes had not been removed for a visual inspection, the fluid was getting back there. So, it seems obvious to me that they didn't check this master cylinder and/or lost a lot of the fluid in there. So much for pros.
Here's what the whole thing looks like. There is a controller of sorts that is actuated by the main brake fluid line. This in turns supply's a large air or vacuum cannister which has said master cylinder attached to it. This master cylinder in turn, supply's the two wheel cylinders on the tag axle.
Is anyone familiar with this setup, or have had any experiences with it?
Also, any ideas on this elusive vent for a Dana axle differential, that I can't find.

[exrench]

The vent can take various forms.Look for a skinny rubber hose hanging from the top of the rear axle -can be anywhere from one end to the other.A less obvious vent looks like a bolt head or a round cap.The service strategy here is to simply reach up and turn it by hand and if it can be turned it is probably clear.Time spent on this is well justified to prevent grief IMHO