The air line needs to be routed so that it won’t kink or snag on anything as the suspension cycles up and down. Make sure to use the blue plastic line. If you use a stronger line, such as braided steel, you can pull the copper tubing out of place inside the differential if the line happens to get yanked on. If the copper tubing gets pulled out of place, you’ll have to go inside the differential to fix it. Again, make sure to use the blue plastic line.