hi all - back again with this 680H. Everything has been working fine. Brakes all of the sudden seem to be locking up on their own. if it doesnt have enough air pressure the brakes will apply, correct? so should i be looking for a leaky hose or is there something else that could be the cause. Already replaced actuators and treadle valves. Some hoses also. Has plenty of shoe and they werent adjusted too tight as it was ok before. Any ideas?
Good air is necessary - as you have already mentioned. If it's not leaking anywhere - the first place to look is the governor. You should be able to replace it using parts from somewhere that sells aftermarket truck parts.
You are correct- just ended up being an air hose. Had one made up and it should be good.
Your question about the brakes being applied when the air pressure drops is exactly how they are supposed to work.
Air brakes are applied by springs. Air pressure overcomes the spring pressure and releases the brakes.
This is true for the parking brakes, but the service brakes are applied by air pressure.