King pin replacement on trailer? What do you recommend?

BoxCarKidd · Apr 8, 2021

SmallPackage said: ↑

The older trailers used 1/4 thick plate. Most newer and heavy spec are using 3/8. Doesn't have to be hardenened. Standard mild is all they use. Hardened steel will destroy a cast fifth wheel surface like a hardened hammer and actually becomes brittle over time. If the pin is a weld in It will be easier to just cut it all off and replace with a new pin with it. If you go thicker plate then what is on it get the proper length pin. They make different shoulder lengths to compensate for the bolster depth. Also it is a great time to custom set the pin depth from the nose. If it is too deep like a lot of older trailers you can move it toward the nose or vice versa.
One custom thing my wife’s uncle used to do at his trailer repair shop on a dedicated o/o trailer was offset the pin a little to the side by 1/4 ,1/2 , or an inch to compensate for the tractor drive axles being offset to one side a little. Made better tracking.
You can actually see this on older trucks. Hook to a trailer and it may overhang to one side more. Usually the right side. Sometimes by 2 inches! This was common on Peterbilt Air Trac and Air Leaf in the 70’s and 80’s.
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Some interesting points there that I never thought about. I saw Mack Ultra Liners that the axles had odd offsets. The tire mileage on those was very good. Go figure?

kemosabi49 · Apr 8, 2021

Happily Retired said: ↑

Usually by the time the plate was shot, like someone said, the trailer wasn't worth repairing. Trailers aren't exactly rare.
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Chemical tank trailers like MC331 and MC307/407 have to have the plate inspected every 2 years. And as expensive as those trailers are it was not a bit unusual to pull trailers built in the 80s. Had one that was a '76.

spsauerland · Apr 9, 2021

Not sure what trailer OP is referring to, but I have removed upper couplers on tanks and frameless dump trailers and have cut and welded new pins or just replaced whole upper coupler if needed. Holland has a bunch of different pins and they are sized according to plate thickness.

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