I have a 95 Mack ch Air leaks behind dash until air pressure drops to 60 pounds then it stops leaking. I’ve removed all front panels on dash but can’t feel where the air is coming from. Also not on the fire wall. Any ideas?
Sounds like it's in the brake system. Hits 60 psi and brakes lock the springs, cutting off the air flow to the brakes so it stops leaking.