Heavy Duty: Floating On Air, Part 1

Make sure your air-ride suspensions are being inspected properly.

“Now, with most elastomeric bushings, they’re free-rotating, and you don’t have to worry about that particular problem, because they’ll zero out at ride height, regardless of what the height is,” Sturmon explains. “Because they’ll turn automatically to whatever position, and as the vehicle moves around, the rotation leaves zero torsional stress in the bushing. And the same is true for metal bushings. But, if you don’t grease the metal bushings, you’ve got a heck of a problem. But the elastomeric bushings, elastomeric urethanes, polyethylenes, are self-lubricating.”


“If you know that those bushings are on a new truck, or they’ve been changed within a year, it’s true that you can inspect them annually,” Sturmon says. “But, if you’re not familiar with the truck, you don’t know the last time they were inspected. And in too many fleets, the documentation for checking torque rod bushings is… I don’t want to say nonexistent, but it’s little or none.

“These things are extremely important because the torque rods hold the suspension in place,” he says. “The suspension is really a system, and like a component of any system, when that component wears out, all of the forces that it’s supposed to protect the system from automatically go to other places. So if the bushing isn’t doing its job, the brackets start to take a beating. Or the shocks start taking a beating. The shocks are in there at a specific location, and at a specific angle, and the rods are supposed to hold that, because if you start putting side forces on a shock, it’s going to go quick.”


“In virtually all circumstances, if fasteners come loose, failures will occur,” says Greg Richardson, vice president of engineering, Reyco Granning. “Pivot connections and u-bolts are some of the most critical areas. And, if a bushed joint comes loose, it can add increased loading to the bushing which will result in premature failure.

“Clamped joints frequently become loose due to motion between mating parts as a result of unforeseen impacts or overloading of the connection,” Richardson goes on. “Once motion has occurred between mating parts, brinelling of materials may occur which allows the parts to ‘seat closer together,’ thus reducing the clamp load of the fastener. Periodic checks of the torque will generally reduce or eliminate a potential failure.”

Although Richardson feels that fleets generally do a thorough job during inspection and maintenance of bushings and fasteners, he suggests the following tips:

  • It is critical that the fleets torque the fasteners to the OEM specifications, and not assume a generic torque for a specific bolt size. An over-torqued connection can be just as detrimental as an under-torqued connection.
  • U-bolts are to be torqued incrementally in a crisscross manner to assure distributed clamp load over the connection.
  • Some connections require torques that can go as high as 800 ft. lbs. This can cause problems at the fleets since many do not have the equipment to measure such levels of torque, and are forced to guess.
  • When bushings are to be replaced, care must be taken not to rip or damage the bushing. Generally the OEM will provide or recommend a lubricant for installation as well as a tool to install the bushing.
  • Proper orientation and positioning of the bushing greatly affects its performance and durability.
  • Proper torque at the bushing connection is critical to its life. Over-torque may crush the core of the bushing.


Bill Nash, manager, technical services, Hendrickson Truck Systems Group, agrees that proper torque is essential, and often left by the wayside.

“On a new truck, everybody’s concerned with making sure the lug nuts are tight, and it’s probably done as part of the PM cycle, but how many people know that in the maintenance manual that the OEM produces and that the component supplier produces, there’s also a (recommended) maintenance cycle for the fasteners on the suspension?” he asks. “It’s critical that they’re checked, and, if broken, replaced.”

Nash fondly points out that there is a 1928 Hendrickson truck in the lobby of the company’s headquarters, and that truck has an original Hendrickson walking beam suspension with over two dozen grease zerks. “You look at our suspensions today, and we have very few suspensions that even have a grease zerk,” Nash says. “So the concept gets in somebody’s head that it’s maintenance free… but it still needs service.

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