Your business rides on eight air springs. They probably deserve a little more attention than...

Your business rides on eight air springs. They probably deserve a little more attention than most fleets give them.

Photo: Jim Park

Air springs are such simple and reliable components; short of a rupture, hardly anything ever goes wrong with them, therefore they are easy to overlook. But looks can be a bit deceiving. It they appear to be intact and holding air, what else would you need to worry about?

During a visual preventive maintenance inspection, mechanics should check for signs of irregular wear, such as abrasion or cuts on the rubber portion of the air spring. It is also important to inspect the air spring for buildup of foreign materials and ensure it is clean and clear of debris.

Foreign material such as pebbles, chunks of road salt and other debris can become lodged in the space where the rubber flex member wraps around the pedestal and cause abrasion of the rubber. Left unchecked, this can eventually wear a hole in the material, causing the spring to deflate.

“In areas where road salt is used, any piece stuck on the pedestal can create friction with the flex member and begin premature wearing of the flex member,” says David Brinkman, director for air springs at Stemco. “Higher performing air spring manufacturers use some type of corrosion-resistant coating, but if there are signs of impact from road debris, these chemicals can begin deteriorating the unit. As well, chemicals used for road surface treatment in winter conditions can negatively impact an air spring, particularly an alloy piston or top plate.” (In 2015, Stemco acquired the manufacturer of Goodyear air springs, as well as Super Cushion and Spring Ride air springs, from ContiTech, a division of Continental Corp.)

A visual inspection of the air spring should include the bead plates – the flat metal plates attached to the rubber portion of an air spring – to make sure the parts are not bent or convex.

“If the bead plates are bent, this could be a sign of overextension from a worn shock absorber or incorrect ride height,” cautions Mark Hilburger, executive director of marketing for air spring manufacturer Firestone Industrial Products. “Mechanics should ensure the mounting hardware is securely fastened and that there is no contact between the air line and the outside diameter of the air spring, as contact with the air lines can cause damage to an air spring.”

Drivers will occasionally tamper with the ride height adjustment to make the truck “ride...

Drivers will occasionally tamper with the ride height adjustment to make the truck “ride better.” Ensure it’s set to factory settings, there are no air leaks, and it inflates and exhausts properly.

Photo: Jim Park

There are a few mechanical issues, more with the truck than the air spring, that need to be checked. A vehicle’s ride height, for example, can affect the life and performance of an air spring.

“If the ride height has been set improperly based on specifications by the original equipment manufacturer, the air spring will not function as intended,” notes Hilburger. “This can cause the air spring to frequently hit the internal bumper if the ride height is too low, or it can cause the bead plate to deform and leak from overextension of the air spring if the ride height is set too high. Improper ride height can also limit the life of the air spring.”

It’s not uncommon to see some misalignment of the suspension or axle to cause the air springs to become cocked to one side.

“This can lead to uneven load on the suspension, which can cause premature failure through overload on one side of the truck/trailer and over extension on the opposite side,” says Brinkman. “This can occur with the misalignment of the suspension, but also if two different manufacturers’ air springs are used that have slightly different ride height specifications.”

Speaking of replacing worn or damaged air springs, replacing the damaged spring like-for-like with the replacement spring will help maintain the performance of the vehicle as well as the expected life of the air spring.

Other air springs may fit into an existing application, but these parts may not have the same load-carrying capacity or stroke length, says Hilburger.

Most of the time, you’ll never need to give your air springs a second thought. Keep it that way by have a close look at them every couple of months. They are simple and reliable parts, but they’re mission-critical, too. If an air spring isn’t working, neither are you.

Inspecting your Suspension

Beginning with the day you put a new truck into service, air suspensions must be inspected and prepared to go to work. Start by verifying the drive axles are parallel by measuring the distance between the axle-centers and the sidewall-to-frame clearance. Then check the ride height for the proper setting and verify fastener torque values are set to the manufacturer’s specification. If those items are all within tolerance, you won’t be putting any undue stress on the suspension components.

The American Trucking Associations’ Technology & Maintenance Council’s Recommended Practice 643A strongly recommends the suspension U-bolt lock nuts be retorqued after the first 1,000 miles, at the first A service (approximately 15,000 miles) and then annually after that for on-highway service, or every 25,000 miles for severe-service applications.

According to Mike Beckett of MD Alignment of Des Moines, Iowa, the average 3.5- to 4-year-old truck with half a million miles on it will have loose suspension U-bolts. This can cause alignment issues and deflect the air spring’s perfectly vertical travel.

“When you see air bags cocked in at the bottom, that usually indicates the U-bolts have stretched and the axle is moving within the assembly,” he notes. “This can be difficult to detect when looking down at the assembly. The usual signs are not obvious from that vantage point, such as rust streaks running from the bolt. Get under it and look.”

Additionally, misalignment of an air spring may cause it to make offset contact with the internal bumper. “This could pinch the rubber portion of the air spring, significantly decreasing the life of the air spring,” says Mark Hilburger, executive director of marketing for air spring manufacturer Firestone Industrial Products.

Additional A- and B-service inspection points should include the suspension ride height and the height control valve, the condition of the shock absorbers, leaks and signs of suspension-related tire wear such as cupping. Annual inspections should include retorquing the U-bolts, inspecting the air system filter (if equipped), and the suspension and shock absorber bushings.

About the author
Jim Park

Jim Park

Equipment Editor

A truck driver and owner-operator for 20 years before becoming a trucking journalist, Jim Park maintains his commercial driver’s license and brings a real-world perspective to Test Drives, as well as to features about equipment spec’ing and trends, maintenance and drivers. His On the Spot videos bring a new dimension to his trucking reporting. And he's the primary host of the HDT Talks Trucking videocast/podcast.

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