Pressure and tension to keep America's trucking fleet in its best condition are aggravated by the economic importance of trucking alone. "77% of American communities depend exclusively on trucks and their trailers to bring them the goods and raw materials they consume and taking away finished products. Trucks carry billions of tons of freight billions of miles every year. Trucks are absolutely fundamental to our lives and only a few of us realize how much. Without trucks, America stops." In the United States it is estimated that there is in excess of approximately 4,500,000 transport trailers pulled by trucks using a King Pin assembly.
And trucking is growing, quite literally. The trucking industry is seeking increases in size, weight, and routes of heavy trucks, including the use of double and triple trailers. These trailers and their trucks can include 18 wheel single trailers that are 53 to 60 feet long. Double and triple trailers can be as long as 120 feet (the height of a ten story building).
In fifty years single trailer trucks have doubled in size. Present federal low limits trucks to a gross vehicle weight of 80,000 pounds. Recent pushes have been to raise the limit to 97,000 pounds. Bigger trucks, longer trailers, and heavier loads are all connected at a single point - the King Pin.
The shear forces applied to the Trailer King Pin and the tractor are enormous. Forces from the constant stopping and brutal contact from the momentum of a trailer moving forward. In the common 2 inch King Pin, anything beyond a 6. 1/4 percent (.125 thousandth of an inch) wear is considered to be beyond tolerable standards and should be replaced. Some countries, such as Australia and New Zealand, require even greater tolerances.
Trailers with worn King Pins are easily identified by their drivers because of the lag, bang, play, and general feel of a deteriorated King Pin. When a King Pin is within proper tolerances and the female end of the assembly is in good condition it is a snug and safe fit.
In spite of being constructed of the toughest, 4140 quenched and tempered forged steel, the average life of the King Pin is between 5-7 years. The wearing rate of King Pins differs markedly between trailer industry segments.
The obsolescence and wear of the King Pin creates a perpetual and inevitable maintenance expense for every trailer operater. The competitive nature of the commercial trucking industry alone drives a constant search for increased productivity and, at a replacement cost of approximately $800 to $3,500, depending on the type of trailer, not only is the King Pin the most stressed part of a trailer, but it is also one of the most expensive to maintain. Also, the trailer is out of service and the operator has to absorb the lost revenue.
Many Trailer King Pin assemblies are replaced every year on America's huge tractor trailer fleet. Until the recent development of a patented King Pin refurbishing process, most every worn Trailer King Pin had to be replaced with a brand new one. The patented King Pin Refurbishing process revolutionizes the maintainance and repair of Tractor Trailer King Pins.
Periodic Motor Vehicle Inspection Manual (PMVI)
A technical presentation with support data was submitted to the Commercial Vehicle
Inspections Project Group and as a result the PMVI Manual in reference to King Pins has been changed to allow: