Every measurement starts at the kingpin
A trailer has no steering of its own. It follows the tractor through the kingpin, the pin under the front of the trailer that locks into the fifth wheel. When a trailer is aligned, its axles are measured against that pin, because that is the point the whole trailer pivots on and pulls from.
That makes the front of the trailer as important as the axles at the back, and it is the end nobody thinks to look at.
A worn kingpin lets the trailer move slightly against the fifth wheel. It does not track as cleanly, and the slack shows up as wear and as a trailer that does not quite follow.
A bent upper coupler. The plate the kingpin is mounted in can be damaged by a hard coupling, a missed fifth wheel or a dropped trailer. If the pin is no longer where it was built to be, every measurement taken from it starts in the wrong place.
A kingpin that is not centered or square. After repair or modification at the front of a trailer, it is worth confirming the pin is still on the trailer's centerline.
An axle can be set perfectly square to a kingpin that is itself out of position, and the trailer will still run crooked.
What to mention when you book
Any hard coupling incidents, any repair to the front of the trailer, and whether drivers have noticed the trailer feeling loose on the fifth wheel. If the trailer has been dropped or the landing gear has collapsed, say so.
Align the tractor at the same visit with heavy-duty truck alignment where it is due, and set several trailers up through a fleet account. The national trailer alignment page covers what the measurement includes.
Other stores nearby
Springfield and Joplin also align trailers in Missouri.
About this store
The Kansas City store runs sixteen services and is managed by Richard Kerber.
See the national trailer alignment page for all 36 locations.