Truck brakes in every purges!!!!

Wild guess... bad treadle valve.

You should be able to narrow the hunt down a bit. Does it happen when you're bobtailing? Does it apply just the primary brakes or does it also apply the secondaries? Can you hear air somewhere if you cut the key off right when the governor cuts out?

 

Once you get chance, stop the truck....pump down the brakes enough to give yourself a chance to see the brake chambers on the rear axle....once it govermer cuts out see if they move. Lets see if we can at least isolate it to front or rear to start...a dryer that doesnt cut out or a higher pressure even (we run 131psi on the vehicles we build) shouldnt put the brakes on

 

Could be faulty ATC valve. When pressure is too high solenoid doesn't stay closed and some air pressure come to the rear wheels. Under normal operation if ATC valve supply air to the rear wheels rear wheels ABS PMV should open to release pressure(brake) on not spinning wheel and keep spinning wheels PMV closed and apply brake to the wheel. So all torque will be distributed to the wheel with traction ( not spinning)
In your case all wheels are spins so all PMV are stay closed until pressure drops down and ATC solenoid sealed.

 

I second the ATC valve being the problem. Is the treadle valve leaking when the service brakes are applied or released? If its leaking when the brakes are applied its probably the treadle valve. When the service brakes are released the exhaust on the treadle valve is open and the leak could be further upstream. Take the service line off the ATC valve and see if air is coming out of the valve as the pressure is building.