Fist of Steel

It’s a chunk of steel about the size of a fist and it’s all that separates you from, well, separation. It’s your trailer kingpin, pound for pound perhaps the toughest component in your truck fleet.

That’s fortunate, because replacing a worn or defective kingpin is a major undertaking. Getting to the mounting hardware under the upper coupler structure involves stripping away a portion of the trailer floor — in most cases, a major endeavour.

An alternative is to have the kingpin repaired. An experienced, professional rebuilder can do the job in about an hour and a half, building up the kingpin surface with a welding rod and then using a portable lathe to machine it down to something as close to the original spec as possible. “As we’re machining it off, the kingpin is cooling down and re-tempering itself.

Basically, as soon as we get out of the way, the trailer is good to go again,” says Terry Playter, owner of TransTech Kingpin Specialists in Barrie, Ont. He says the kingpins he rebuilds wear the same as original components, and he guarantees that you won’t fail your next annual inspection because of a kingpin defect.

TransTech charges a flat fee per rebuild — about $300, an enticing price compared with the costs associated with several days in the shop. It’s easy to be consumed by the economics of the replace-or-rebuild decision. Usually, a kingpin doesn’t show significant wear until the trailer is well into its on-road service life. Unless it’s a unit you plan to keep for a while, you may feel reluctant to invest in an older trailer.

But is it safe to rebuild a kingpin? Sam Martin, executive vice-president of The Holland Group, which produces kingpins and fifth wheels, says no. It’s a position backed up by two major industry groups, the Society of Automotive Engineers and the Truck Trailer Manufacturers Association, which recommend replacement if the kingpin shows wear of an eighth of an inch or more in diameter.

There’s more to a kingpin than the stubby steel knob extending from the upper coupler plate, says Martin. “What you can’t see is the extent of potential damage and other things that are going on in the rest of the kingpin structure, the part that’s built into the upper coupler structure itself,” he explains. “If you rebuild, you’re just filling in the gaps on the exposed part of the kingpin. You haven’t necessarily made it structurally sound.”

Another concern, Martin notes, is consistency. There’s no question that someone who knows what he’s doing can do a good job rebuilding a kingpin, he says. But Martin doubts it can be done well time and time again from trailer to trailer.

“Additionally, there are at least five different chemistries or alloys that are used in kingpin construction here in North America, and in that there is a considerable range in the carbon content, which is the element that causes the biggest variability in the welding process and welding success,” Martin says.

Even if the kingpin rebuilder’s technique is sound, variations in the alloy from pin to pin make it hard to assure quality control across the fleet.

Martin and Playter agree that whether you rebuild or replace a kingpin, don’t take the decision lightly. You’re dealing with an important piece of hardware, so learn what constitutes excessive wear and tear and don’t trust your kingpin repair or replacement to any old Joe Blowtorch.

“A lot of mechanics will just wipe off the grease, look at the kingpin, and say, ‘Yeah, this one has to be done,’ or ‘No, it doesn’t,'” says Playter. “That’s about as technical as they get.”

Of course, there is a way to stay out of the kingpin rebuild/replace debate altogether: spec the right fifth wheel for the job and keep it maintained and adjusted. Unlike that hunk of steel peering out from above the upper coupler plate, a fifth wheel is completely exposed and its working parts are easy to inspect and replace. Take advantage of it.On a high shelf somewhere, you probably have a plastic or aluminum no-go gauge to check the integrity of your trailer upper coupler plate and kingpin. Haul it down and use it –inspection and maintenance of these items is just as important as the inspection and maintenance of the fifth wheel. The following procedures are based on recommendations outlined in SAE J2228 and from kingpin maker Holland Hitch (also a source of kingpin gauges). They should be completed every three months, or 30,000 miles.

1. Upper Coupler Plate Flatness: Using a 48-inch straight edge, check for flatness in all directions. Bumps or valleys will create an uneven load on the fifth wheel, which could damage the top plate and lock.

2. Kingpin Straightness: Use your kingpin gauge or a carpenter’s square to check the kingpin’s straightness; it shouldn’t exceed 1 degree from square in any direction. A bent kingpin accelerates lock wear.

3. Kingpin Length: Use your kingpin gauge to check the length, especially if you’ve added a greaseless lube plate (you may need a longer kingpin to compensate for the thickness of the material).

4. Kingpin Wear: Inspect the kingpin for any nicks, deformation, or cracks, and its mounting for looseness. Don’t allow wear exceed 1/8 of an inch in diameter.