Misterious air leak

Never tried that.
Which side is leaking primary or secondary?

 

I gave up looking for mine. I’m good if I keep enough air for about an hour.

 

Type of truck..?

 

When you checked the air bags were you loaded?
Did you put your ear up to each brake chamber listening for leaks?

 

They sell these microphones on a stick that you can use to magnify sound. Might be able to find it that way, if it bothers you that much.

 

I've two over the years that took a while to find. One was a line behind the dash and the other was underneath the seat for the air ride.

 

Guessing that your truck is plumbed the same as the 2014 t-680 I got rid of.
Let air build up, set brakes and then shut it down.. Watch the gauges..once primary tank gets down to 90 it’ll stop feeding your secondary tank. At this point you should be able to see if the primary or accessory tank is leaking by whichever tank keeps dropping.

Imo, you just have push fittings that are worn out and leaking.. I had to replace almost every one on my 680 after 5-6 years. Colder weather makes them worse..

Personally I’d just get a spray bottle filled with water and a lot of dish soap ( I keep one filled in my truck) and start checking every single one.

Could just have a bunch of slow leaking fittings vs on big leaker. Only issue I had replacing some fittings was there not being enough slack to trim a half inch off the ends before putting the new ones back on.

 

I’ve mentioned this in many other threads and usually get blown off but I have found that 80% of mysterious silent air leaks are thru the transmission. The solenoids or the range selector or splitter valves will leak and let air pass into the trans and leak out of its vent. To prove it years ago i put a ball valve on the trans supply line on one of my trucks that would not hold air for half a day even after everything on air system was tightened up. With air shut off to trans when parked truck will hold air for weeks now and it takes a full week before it drops from 120 to 60. Has air ride. If i leave valve open it is down to zero in a few hours time.
Another thing is seats. They leak over time. Put shutoffs to them when not in use. But air shifted trans are big culprit's.