Field Repairs of Tractors and Trailers for the Driver/Trailer Air Lines
Trailer Air Lines 
Problem 1: Air Lines Hang Too Low 
Trailer air lines must be 18 inches above the ground. A common problem on 53 foot trailers is that the sliding process damages the hanger springs causing the air lines to hang too low or actually touch the ground. This is a significant problem since the air lines can develop holes causing the spring brakes to come on and stopping the vehicle. When going through Weigh Stations, Weigh masters can easily see air lines that are hanging too low and are likely to stop the rig.
Solution 1A 
Use nylon string to attach at the spring attachment points both on the air line and on the underside of the trailer. A slip knot should be used on one end so that the string can be easily detached when sliding the axles. Be sure that no string or spring is hanging low.
Solution 1B 
Sometimes a stretched out spring is the problem. High quality side cutters can be used to trim the spring and a plier used to bend the end through the attachment point and then wrap bitter end around the standing end of the spring.