Guess I didn't explain correctly about letting it build back up. I was referring to speed or RPMs. Yes, if you loose brake pressure your brakes will lock up. The only problem is that if your brakes are to hot even if you loose air the brakes will not stop you. That is what is called brake fade. Yes, I found that out the hard way coming down I17. from Flagstaff to Phoenix AZ. I was an otr driver and had no engine brake or exhaust brake.