E&MU: Keep Air Spring Suspensions in Shape

By Eric Brothers, Contributing Writer

This story appears in the January/February 2011 issue of Equipment & Maintenance Update, a supplement to the Jan. 17 print edition of Transport Topics. Click here to subscribe today.

Air suspensions softened the jarring ride that drivers and cargo suffered for decades, but they brought with them maintenance issues that demand constant attention.

Debris kicked up from the road can inflict serious damage, as can suspension parts and other components that rub against air springs while trucks roll down the highway.

The threats are compounded for adjustable ride height applications, where underinflation and overinflation can create unique maintenance challenges.

The many factors that can shorten an air spring’s life have compelled many fleets to educate their drivers and technicians about proper care and how to spot potential trouble.

“One major reason for failure is punctures,” said Kenny Hughes, field service manager for Reyco Granning Suspensions, noting that it’s essential to keep the area around springs free of debris to prevent chafing and premature wear. 

Routine visual inspections are one of the best ways to spot and clear away that debris, said Dave Vanette of Firestone Industrial Products Co. Vanette said a proper inspection involves scanning for any signs of irregular wear, tears or heat cracking on the spring rubber and determining that nothing is touching it or interfering with its movement.

The inspection should include checks for buildup of dirt, debris, rust or any kind of corrosion on the piston that can create a surface rough enough to rub through the bellows. It is also a good idea to check for oil, grease or dirt buildup on the spring.

Liftable suspensions that routinely have either the primary or lifting springs deflated may be more susceptible to collecting debris, Hughes added. Also, springs in van slider suspensions that can dump air to prevent dock walk may collect gravel, sand or other road grit that will scrape the exterior when the air springs deflate.

A basic inspection should be done any time from daily to once a week.

Cleaning of the piston and air springs should be done with soap and water, methyl alcohol, ethyl alcohol or isopropyl alcohol. Vanette said these are the only industry-approved cleaning solutions for air springs. Organic solvents, open flames, abrasives or direct pressurized steam for cleaning air springs should not be used.

Other components rubbing against the spring’s flexible members are another trouble spot to watch. Interference can come from shocks, mounting brackets, battery boxes or tool boxes. And the culprit doesn’t have to be metal; air hoses and brake lines can come loose or be improperly routed; even a plastic air hose eventually will rub through the rubber bellows.

“The worst thing could be a rubber hose because rubber-on-rubber will grab and chafe,” said Bill Hicks, global director of product planning for trailer suspension and axle brake systems for SAF-Holland. He added that suspension manufacturers work closely with OEMs to make sure they identify and eliminate any interference in the vehicle’s design that could invite abrasion. “But upfitters or dealers may install additional components that could interfere with the suspension package during axle movement and cause premature failures,” he cautioned.

Vanette added that bushings may wear out and cause abrasions or tears in the rubber bellows due to misalignment of the air spring. “The most common problem found in non-warranty air spring product returns is overextension of the air spring, typically caused by a broken shock absorber,” he said. “When a shock absorber breaks, it allows the air spring to travel too far and essentially tears the air spring apart.”

The first thing to do when trouble-shooting air spring suspension problems is to check the ride height, said Jim Rushe, program manager for on-highway products at Hendrickson Trailer Suspension Systems. “A lot of people fiddle with the ride height. From our experience, it’s the main thing that causes a lot of the problems, so know how to set it correctly,” he cautioned. “Get the ride height in an acceptable range for that product.” 

Setting ride height too high puts the air spring too close to its maximum extended length and risks having it come apart. If ride height is set too low, the piston constantly beats against the air spring’s internal bumper and can damage other vehicle components.

“People add dump controls on a suspension, which is all right as long as they remember to reinflate the suspension,” he added.

After dumping the axle to maneuver, they sometimes forget to air it back up, which can cause problems. He also warned against overloading the trailer, which can damage air springs and their mounts.

He also recommended, “If you are lifting a trailer onto a flatbed railcar, exhaust the air springs so they won’t go to their full extension and possibly come apart.”

As with all wear items, air springs occasionally do have to be replaced. The key is to get the correct replacement air spring, Hicks emphasized.

“With thousands of possible air-bag designs in use by suspension manufacturers, matching size and features is important to ensure proper performance of the air suspension system,” he said.

Hicks recommended using a genuine replacement part from the suspension maker: “There are some aftermarket sources that provide air springs that may or may not fit. If there is a mismatch, then you’ll have continued problems such as restricted motion, leading to a rough ride.”

Hendrickson’s Rushe offered similar advice: “There are some differences in how air spring flex members are constructed — including the length and stroke of the air spring. The piston mounting can fail or cause damage if the wrong air spring is used. Will-fit parts may appear correct, but their internal parts, such as bumpers, might not be the same.”

Still, there are many reputable aftermarket sources in the industry, such as the suppliers to the suspension manufacturers. Cross-reference lists for part numbers are readily available.

After obtaining the correct replacement part, the next step is installing it properly. Make sure the fasteners are correct, use the right torque and mount the air spring as directed. “If spacers above or below are needed and they are not in place, the air spring could travel incorrectly and be damaged,” Rushe noted.

“When properly maintained, air springs can provide cargo protection and flexibility, enhanced safety, a more comfortable ride and longer vehicle life,” Vanette concluded.

If an air spring is installed properly and maintained, it can go more than a million miles and last five or more years before it has to be replaced, SAF-Holland’s Hicks said.