For the best cable support for most combination assembly setups, Phillips Industries recommends that you use two separate tender spring assemblies instead of one.
The spiral design of coiled cables expands and contracts like a spring as the truck moves, but this is not the case with straight cables. Instead, the movement of straight air and electrical cables is only as good as the spring(s) and their positioning on the cables that suspend them above the deck plate.
With a two-spring setup, a combination assembly is formed to create a loop that expands and contracts, similar to how a coiled cable or air line works, but on a much simpler and larger scale. A tender spring is placed at the beginning and end of the loop. The first spring acts as the support spring, and the second as the working spring. It should be noted that although guidelines for installation of an assembly in this type of setup will be similar, they will vary from fleet to fleet, and vehicle to vehicle, because tractor-trailer applications are not cookie-cutter.
Support tender spring
In a two tender spring application, the supporting spring hose holder is placed at the beginning of the loop following the tractor side connections. It plays the role of supporting the electrical and air line leads from the back of the cab that will remain primarily stationary, and setting the start of the loop for its best working position. When the vehicle turns, the support spring should do minimal stretching. If it’s doing a significant amount of stretching, the hose holder needs to be placed farther back, closer to the tractor connections to decrease the lead length, or the spring is too short, or both.
Working tender spring
The working spring does all the stretching and the majority of the sliding on the tracker bar. It should always be placed on the right-hand side (passenger side) of the support spring when hanging from the back of the cab. The working spring’s hose holder should be connected at the end of the loop, or where the assembly comes full circle to meet the first hose holder. With the supporting spring holding the stationary portion of the assembly in place, the working spring will stretch and recoil as the loop in the middle of the combination assembly expands and contracts with the vehicle’s movement.
Importance of the two-spring setup
Although not all back-of-cab systems with combination assemblies require a two spring setup, most will benefit from this type of cable support. With quality springs that are the proper length, severe turns and jack-knife situations are better accommodated. Cables are kept off the deck plate because tender springs are less likely to overstretch, avoiding potential CSA violations.
This Tech Tip was contributed by Phillips Industries.