A couple Fridays ago I hooked up to my set and completed my full pre trip and proceeded out of the yard, on my first heavy brake application I felt my brakes were not reacting correctly. I then drove round the block and again tested them using only the spike. I found that there was approx a 200 hundred foot delay before my brakes reacted at about 15 mph. I headed back to the yard and began looking under my trailers for any problems. I found one of the main brake lines had been replaced but was completely twisted, allowing very little air to the brakes. I later found out that the trailer had been just serviced by our outside mechanic. Before you say it, yes I did do a tug test in the yard before leaving and the brakes did lock up as required. I found it to be only on a heavy brake application that there was any delay. Any opinions on this????