FMCSR 393.70 - Pivoting Lower Fifth Wheel

FMCSR 393.70 FIFTH WHEEL COUPLING There is a need for clarification of 393.70. We are finding that certain carriers (primarily aggregate haulers) in the Harris County area are operating truck tractors with pivoting lower fifth wheels. The carrier's trailer is often also equipped with a pivoting fifth wheel. The carrier's will often have no device or a defective device in place to prevent the lower fifth wheel from pivoting causing the trailer to jolt backward several inches on acceleration or forward several inches on deceleration.

The jolt to the upper & lower fifth wheel devices causes excessive stress on the kingpin that I do not believe it was designed to absorb. Those stresses are transferred to the rest of the upper and lower fifth wheel assemblies. Unless the lower or upper fifth wheel assemblies are already damaged there is no recordable violation for this obvious safety issue. Kingpins are not an easily inspected part of the equipment as the trailer must be uncoupled to provide a proper inspection.

Include in 393.70 a provision that a pivoting lower fifth wheel cannot be coupled to a pivoting upper fifth wheel. Add a provision that a pivoting lower fifth wheel may be used with a pivoting upper fifth wheel coupling if a device is used to prevent the lower fifth wheel coupling from pivoting forward and rearward with the longitudinal axis of the truck tractor or truck.