Air Pressure Alarm Question

I have a 2006 Freightliner Columbia and the issue that I'm having is that my trailer brake (and only my trailer brake) will pop right before my low pressure alarm sounds. My alarm will sound at about 80psi which sounds about right [I think but could be wrong]. Both trailer and tractor should pop at about 60 or 40psi right?

I just replaced both my air dryer and governor (both came as an assembly) - Bendix AD-IS 800383. Even though it claims not to be adjustable I'm wondering if I can/need to manually adjust it, or is there some other problem I should look at? Thx

 

What about the dash valves? I just watched a youtube vid that said that the dash valves is what controls the psi at which the knob pops out. And where is the trailer protection valve located? How does that differ from the Tractor Protection Valve in terms of function?

 

Thanks LB. It's a Bendix MV3 Dash Vavle Module. There are different models and as far as I can tell the differences between them simply lay is the fittings used. I want to say that the ports themselves are the same across models and take a 1/4 npt male fitting. My particular model uses 3/8 PTCs (push-to-connect) and the dealer wants $220 for it. The same model online isn't much better with $175 being the lowest. However, I can buy a different model for $100 and hopefully switch out the fittings and faceplate. I'll buy the one from the dealer just to have on hand in case I get stopped or the valve stops working completely while I wait for my online (cheaper) one to arrive.

As far as the alarm goes I'll retest once I have a properly functioning valve. Duramax you are correct about 60psi, but while reading up on the switch that controls it I believe some are made to sound at different psi's. But even if I'm wrong about that, so long as the alarm sounds I should pass. Given how quickly air escapes out of these trucks, an alarm sounding at 80psi gives me more time to react than one at 60psi.