Watching Your Back

Inspection guidelines for trailer air suspensions.

"If that is neglected," Barton warns, "the hanger typically has to be replaced, along with the bushing, the bushing fasteners, and in some cases the beam may have to be replaced. It gets to be a very expensive ordeal, especially when the hanger is welded on; you have to torch it off, grind it, and weld on a new hanger.

"Typically, these pivot bushes are tucked inside the hanger," he continues. Because of this, Barton says, in cases of suspected wear, the technician may need to actually break the pivot bolt and drop the beam and bushing down to perform a proper inspection. "You've got to make a judgement, because it's so hidden in the hanger. It's difficult to see, and you have to look for excessive play."

Finally, Barton explains, technicians should be inspecting shock absorbers, as they provide crucial damping in an air suspension. "If there are complaints about vibration, the first thing to look for is whether the shock absorbers are worn out," he says.


Dana's Fulkerson advises technicians to look for anything that might be rubbing on the air springs. That includes any line or wiring that might be working loose and rubbing or scrubbing on components. He also advises that technicians look for cracked or loose components, loose fasteners, or cracks in any of the structural members.

Like Barton, Fulkerson urges technicians to pay close attention to the condition of the air bellows and the shock absorbers.

"Good air springs, just like on the tractor, I'd say they'll go for three, four, five years of good use," he explains. "It all depends on the applications, too. You'll get into places where the roads are considerably worse, and if you've not done good maintenance, and you've got worn shocks, then your air bag is going to take a much worse beating than if you had good shocks. If the shocks are actually leaking, or starting to wear out, the bags tend to pound down a lot more."

Of course, a visible leak or a wet spot on the shock indicates a problem, but what if there is no external sign of wear?

Fulkerson offers a simple test: when the truck comes in from the road, the driver should feel the shock's casing for warmth.

"What we recommend to drivers is, after you've been out on a long haul, reach in and grab onto the bottom of the body of the shock; if the thing is the least bit warm, you know that the valving is working," he explains. "If the shock is actually stone cold, or ambient temperature, more than likely the valving is worn out inside or it's had some sort of problem and lost fluid."


According to Fulkerson, the driver plays a crucial role in spotting trouble signs from the trailer's suspension. "A driver ought to be catching loose fasteners, anything that looks like it's rubbing or chafing," he says.

And, once out on the road, the driver also has first watch over the trailer's suspension. All he or she needs to do is keep looking in the truck's mirrors.

"Probably the easiest thing for a driver to see is whether a trailer is dog tracking or not," Fulkerson says. "If I look in one mirror and I can see this side of the trailer, but I'm looking in the other mirror and I can't see the back corner, something's wrong. That's probably one of the most visual things that a driver can pick up."

Simple enough. But Fulkerson cautions that this visual inspection may not be effective with some newer trailers:

"It's gotten a little harder because of the wide-based trailers that have come out," he says. "The old 96-inch trailers, when you were looking in the mirrors you were looking right down the sides of the trailer. A lot of the trucks now, unless they've got the mirrors really stuck out there, you won't look straight down the sides of the trailer.

"More than anything, it's issues with alignment or tire wear," he says. "Somebody calls in complaining about tire wear and you start asking them questions about the alignment—do they do routine alignment checks or anything—and more than likely that's the thing that's really neglected. They'll take the time to align a tractor when they see steer tire wear, but they don't think about it on a trailer, but it's just as critical. When it comes to fuel economy and tire wear, make sure the trailer is following where it's supposed to be."


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