According to a Frost and Sullivan fleet survey taken a few years ago, fleet managers rated “reduced maintenance requirements” as important as “fuel efficiency” in the Top 3 rankings of benefits for powertrain technologies. While manufacturers have been moving in that direction for years, it’s safe to say that the maintenance-free tractor-trailer is still a few years away.

In terms of suspensions, the only two big maintenance items we have left are shock absorbers and air springs. Some of what historically were large maintenance items are designed to almost out-live the trucks themselves. Things like main pivot bushings on a trailing arm suspension now come with five- to -seven-year warranties. You can almost forget they even exist.

Almost.

Things like air bags and shocks need regular inspections and occasionally maintenance or replacement. The heavy stuff like bushings, torque rods and spring packs are usually good for the first life of the vehicle now, with many warranted out to 500,000-750,000 miles (800,000-1.2 -million kilometres). But the parts that move or rub up against other parts do need to be checked – like steering kingpins, and spring shackles.

Also, it’s highly advisable to retorque some of the suspension components a week or two after the vehicle goes into service. It can make a big difference a year and a half down the road, especially in severe service applications.

So, while much of the undercarriage is now more or less maintenance-free, here are a few places that still need a close eye from time to time.

Steering components

Whether on the tractor or the trailer in the case of a self-steering axle, steering kingpins need a fresh supply of grease on a regular basis, says Claude Sauriol, Canadian sales manager at Ridewell Corporation.

“Seized or binding kingpins are a fairly common complaint,” Sauriol notes. “Kingpins that don’t move freely can cause excessive tire wear and handling issues. They make it harder to turn and they will cause the tires to shimmy when driving straight.”

He recommends using a manual grease gun rather than an air-powered gun that won’t always flush out the dried and caked grease in the joint. He also says, as strange as it may sound, greasing steering components isn’t a job for your high-school intern, at least not until they have been properly trained.

“The old grease has to be purged and you have to know that’s happening,” says Sauriol. “Somebody just squeezing a -couple of shots of grease into the fitting may not be getting enough in there to push the old grease out. It’s not a difficult task, but it needs to be done properly.”     

Ride-height valve

The other essential component in an air suspension system, the leveling valve, isn’t necessarily a maintenance item, but it should be checked for proper operation.

“It’s essential for maintaining proper ride height as set by the vehicle -manufacturer,” says Randy Petresh, vice-president of technical services at Haldex. “Ride height isn’t a user–selected parameter based on preference. It’s there to maintain proper driveline angles and maintain the correct height of the trailer.”

Since these are pneumatically operated mechanical devices, they are subject to air contamination, corrosion and possible physical damage. Proper operation can be determined by cycling the valve through its extremes, and ensuring the moving parts are not binding.

“You can check the correct adjustment by referring to the maintenance manual to determine proper ride height,” Petresh says.

Normally, once these have been set to factory spec’s, they don’t need much adjustment, but then along comes a driver. Those who sit in a cab have been known to “adjust” leveling valves in -pursuit of a “softer” ride. Not only will tampering with the leveling valve not produce a smoother ride, it could wreak havoc with driveline angles, U-joints, and steel springs in an air-over-spring configuration. 

Air spring inspection

Like tires, air springs often exhibit signs of wear caused by some other problem. Worn bushings, for example, can cause a misaligned air spring, which can result in holes caused by chaffing against other components or a loose internal bumper. The most common problem found in non-warranty air spring product returns, Firestone advises, is an over- extended air spring caused by a broken shock absorber.

“When a shock absorber breaks, it allows the air spring to travel too far and essentially tears the air spring apart,” says Firestone’s manager of new business development, Dave Vanette.

Among the more common problems with air springs are circumferential tears at the top or bottom of the spring, caused by over extension. These are often the result of an inoperative leveling valve or a faulty pressure regulator. 

Aside from obvious damage, air springs should be checked for air leaks, the presence of abrasive material in the vicinity of the piston that could wear a hole in the sidewall, and built-up oil or grease on the rubber. The air spring should be cleaned with soap and water, methyl alcohol,
ethyl alcohol or isopropyl alcohol – the only industry-approved cleaning solutions for air springs. “Never use organic solvents, open flames, abrasives, or direct pressurized steam to clean air springs,” Vanette advises.

Maintaining shock absorbers

Even the best shock absorbers won’t last forever, though one might not suspect a problem from outward appearances. The American Trucking Associations’ Technology and Maintenance Council’s Recommended Practice RP 643 strongly recommends replacing shocks when installing new tires. It stresses that no two operations or vehicles will see shocks deteriorate at the same rate, so pre-determined mileage recommendations are not that useful.

Visually inspect the shocks during the “A” service, or every 10,000 – 20,000 miles (16,000 – 32,000 kilometres). Examine the shock body for damage such as dents and cracks. Inspect the mounts and bushings as well for deformed or loose components, and watch for raw oil leaking from under the dust tube. An oily residue on the shock body is acceptable and considered normal under some conditions. Liquid oil running down the shock body demands
a replacement.

During the “B” service, check the body of the shock for elevated temperature after a short drive. It should be obviously warmer than the surrounding hardware. If not, it’s not doing its job, and has likely failed. Consequences of running on failed shocks include a deteriorated ride, excessive vibration, and eventually cupping the tires’ shoulder ribs. Hopefully, you catch a failed shock before it begins to wear out your tires. 

And finally, if an alignment is in order, don’t bother sending it to the alignment bay until all the suspension components have been inspected and restored to original spec’s.