Watching Your Back

Inspection guidelines for trailer air suspensions.


When it comes to suspension maintenance, "Tractors tend to get a lot more attention than trailers do," says Tim Fulkerson, technical service specialist, Dana Corporation. As a guy who spends a lot of his time poking around under trailers, Fulkerson sees the results of negligent trailer suspension maintenance all the time. "They just don't get the type of PM and inspection that the tractors do."

According to Fulkerson, there are two main reasons for this. First, fleets tend to bring their trailers in for PM inspections far less often than they do their tractors. Second, many fleet maintenance shops that have traditionally serviced older trailers with spring suspensions tend to consider trailer suspensions low-maintenance items, and that attitude carries over when the fleet switches over to air ride trailer suspensions.

"Back when you had the old spring ride trailers, they didn't get a whole lot of attention," he explains. "If you've got fleets or shops that are dealing with the new ones the same way, they're missing a lot of opportunities, because routine maintenance and inspection are really critical, because air suspensions are more complicated than the old springs."

MISSION CRITICAL

Bruce Barton, director of engineering for Ridewell Corporation, agrees that trailer air suspensions are too often the victims of neglect. "It is very obvious to us as a manufacturer that, irregardless of the information that we put out—our service manuals, our drawings, any maintenance requirements, like periodic re-torqueing of the fasteners—nobody follows it," he says.

"If there's one thing you could get across, it's: ‘Read the manufacturer's service literature, and follow it,'" he adds. "I can't tell you how many times pheyeople say, ‘I didn't know I need to re-torque!' Well, it's right there in the service literature! I don't know why it is, we just continually get calls here, ‘Hey something's loosened up here.' Well, gee whiz, did you re-torque at 6,000 miles, like we recommend? ‘Oh no, I didn't know to do that.'

"Number one headache is the pivot bolt fastener maintenance," Barton says, "That is the single most common lack of maintenance we see. All fasteners will lose some of their torque over time... and the first re-torque is the most critical re-torque of that fastener.

"We like technicians to use a torque wrench," he adds, "but most of them will just use an air impact wrench and just guess at the torque level, and let the chips fall where they may."

THREE COMPONENTS

Looking at the typical trailing-arm air ride trailer suspension, Barton breaks maintenance inspections down by the three main "consumable" components that need your technicians' attention: the air bellows, the pivot bush and the shock absorbers. "From a mechanic's standpoint, they have just got to do a visual inspection of the air suspension," he maintains.

Barton says that the first thing for technicians to look for is air spring abrasions. Because it is a rubber element, the air spring is subject to fatigue cracks in the areas where the flex member rolls over its mating part. Additionally, road debris could be thrown up and abrade or puncture the rubber bellows. "These rubber air bellows, they do have a finite life," he explains. "A lot depends on how rough the service they're in, but the air bellows needs to be inspected periodically."

The next main element in the suspension is the pivot bush. "This is typically a very large rubber bush that is up at the leading edge of the trailing arm," Barton explains. "That is a rubber element, and it is considered a serviceable item. The bush is typically pushed into the beam portion of the suspension: it slides into the hanger, then there's the pivot bolt that actually attaches the bushing to the hanger." To Barton, this may be the most important part to inspect. He recommends that technicians look for excessive play at that bush, especially if the driver has complained of the axle wandering or walking; both are pretty sure indications that the pivot bush needs to be replaced.

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