The outside of the air spring can suffer from abrasion if it rubs against any other suspension part because of misalignment or other parts out of their normal positions, like a broken shock. Too little pressure or foreign material from the road can also be the cause.
Air springs, like tires, have rubber plies and cords. And, as with tires, it’s the contained air pressure that carries the load, and not the container itself.
Proper inflation and alignment are the two biggest issues in air spring maintenance. Incorrect pressure creates damage mainly because it causes incorrect ride height. Springs that ride too low will rub against adjacent parts, fold over and abrade, or may even burst the hoops that divide some air springs into sections. When overinflated, the spring cannot absorb normal motion and may tear away from mounting plates.
Firestone Industrial Products Co. confirms that proper spring maintenance goes beyond the springs themselves. “The vast majority of premature failures and consequent warranty returns are found not to be defective, but fail because of abuse caused by other problems associated with the suspension,” says its website. Routine inspections of springs and the suspension system will go a long way toward keeping your ride smooth.
INSPECTING AIR SPRINGS
Inspect air springs at the same interval other suspension components are checked, says Firestone Industrial Products’ technical director, Steve Lindsey. Howard Adkins, technical service manager for Hendrickson Trailer Suspension Systems, recommends a cursory inspection every 30 days, and 90 days for a major inspection. Ted Solida, a product manager for Triangle Air Spring, recommends a cursory look as part of your daily walk-around, and getting under the truck as frequently as weekly.
Adkins recommends first making sure the trailer is at ride height. Then look for “external wear, clearances to tires and any other component, obvious deterioration, or lodged road debris.” He recommends an accurate check of ride height at those 90-day intervals. Firestone recommends checking clearances “around the complete circumference of the air spring,” which often requires crawling and bending.
All sources recommend a careful check of the lower air spring piston on “rolling lobe” type air springs. Solida says, “Make sure the piston is clean, not rusted, and that it is free of debris.” Debris or rust makes it “like sandpaper,” so the spring will be abraded almost as if it were rubbing a tire. Keep road salts and mud, and the resulting corrosion, off with regular cleaning. Since the surface of the bag may also get dirty, clean it as well. Don’t use petroleum solvents or steam. Soap and water are best; alcohols are okay.
“Listen carefully for leaks,” Solida says. “If you hear anything at all, you’ll know a spring needs to be replaced.” Even with no leaks, inspect the entire outside surface of the spring for signs of abrasion from the piston or a nearby shock, tire, suspension member or air line. Look also for heat cracks. Inspect for bulges in the bellow, which can result from a failure due to contaminated air in the brake system. This would come from an air dryer malfunction or compressor wear.
Inspect the girdle hoops on convoluted designs to ensure they are in correct position. If the rig’s riding too high, this often tears them off where they are vulcanized to the bag, causing them to lose their even spacing and sit in a cocked position. A low ride becomes especially abusive to convoluted bags if the driver runs off a curb, which can create a vacuum inside the air bag.
Holes rubbed through the side of the bellows may also result from suspension misalignment due to worn bushings, causing the bumper to hit the side of the bag when you hit a bump. Or the suspension misalignment can be due to interference from suspension parts. Bead plates can bend because of misalignment.
Check for cuts and separation where the bag is crimped or vulcanized to the top and bottom plates. These can result from overextension due to riding too high. The plates can even be bent into a convex configuration.
Finally, check for impending failure – a tear partway through due to a sharp object like a rock thrown up off the road. While you can’t always prevent such problems, it helps to go slow on unpaved roads. Stone guards can be added if this is a chronic problem.
INSPECTING THE SUSPENSION
After checking airbags, look over related suspension parts. If loading something heavy onto the trailer, run the engine in order to keep the air bags fully pressurized, suggests Solida. Then, watch what happens right after the weight hits the deck. The trailer will first drop, but then the valves should react and bring the trailer back to its normal height. If not, you have an air valve problem.
First make sure that the truck has not been loaded beyond its rated capacity. Then make a precise height check. “Maintaining proper ride height is important to prevent dynamic wear from possible tire contact or suspension beam contact (if the suspension is running below ride height), or over-extension tearing at the top plate (if suspension is running above ride height),” says Adkins. Such over-extension can even damage the shock and its mounting, he adds. Hendrickson lists the ride height on the model ID tag, Adkins notes. Specs should also be listed in the owner’s manual.
If there are problems with ride height, inspect the linkage that operates the height control valve. Bent parts must be replaced.
It’s easy to check if the valve is working. Disconnect the linkage and pull the actuating arm down to see if air is then introduced into all connected air bags. Push the arm upward to close off the air supply and dump air pressure. If the valves work in both directions, and the linkage parts look straight, everything is okay. Replace bent or broken linkage parts with new ones. Valves are adjustable, but should not be adjusted to compensate for bent linkage parts.
Solida says air valves bear a careful look-see every time you do a major inspection. They should be cleaned and, if necessary, replaced frequently because they work hard and often don’t last long. Clogging and corrosion due to moisture in system air is often the cause.
If an axle or tandem leans down on one side, check for air valve clogging, says Solida. Inspect all aspects of the suspension and all air lines for adequate clearance from the air bags. Inspect tires for loose tread, which can tear air springs.
Some suspensions require periodic torquing of bushings. Check torques and then check the bushings by having someone drive the truck slowly on a very bumpy road as you watch. If there is obvious side-to-side motion, the bushings are worn. If this is impractical, pry the trailing arm to one side and the other to see if it’s easily moved. If the bushing keeps it aligned, it’s okay.
Inspect shocks for fluid leaks and broken or worn end bushings or eyes. Shocks protect air springs from overextension by both their maximum length and their dampening ability. After a long run, shocks should be warm to the touch. Cool-running or damaged parts mean shocks (or replaceable bushings or bolts) should be renewed. Chronic shock and spring tearing and breakage from overextension may mean you need a restraint system to limit axle travel.
Also check and torque all suspension mounting nuts and bolts. Torque only to manufacturer’s specifications, not by feel.
Don’t take an out-of-sight, out-of-mind attitude about air springs. Frequent inspections and simple care will go a long way toward keeping them up to speed and keeping you on the highway.
HOW TO REPLACE AIR SPRINGS
Once your rig is adequately supported, it’s easy to replace the bags by unbolting.
First run the engine, pressurize the air system, and make sure the unit is at normal ride height, says Ted Solida of Triangle Air Spring. Then install support jacks and wheel chocks. Finally, fully depressurize the system to make it safe to disconnect the air supply to the bag being replaced.
Thread fasteners carefully to avoid cross-threading and similar damage. Torque to manufacturer’s recommendations to make sure everything is tight enough to hold, but parts won’t be distorted.
When should a bag be condemned? “The air spring should be replaced if leaking or viewed to be abraded through multiple layers of the flex member (or bellows),” says Howard Adkins of Hendrickson Trailer Suspension Systems. Replacement is also necessary if “either the upper or lower mounting attachments are worn from operating loose or if the air spring flex member has separated from the lower piston or top plate.”
Other reasons for condemnation are “significant deterioration of any kind of the top plate or piston,” Solida says. If equipped with plastic pistons, the unit needs replacement when there are any cracks, as these often leak. Also check for damage at the air line connections, which are either straight or elbow-type fittings attaching at the chassis at the other end. Replace if damaged or leaking, unless the fitting can just be torqued. Severe cracks or a cord showing mean you should replace the unit.
SMART AIR SPRING OPERATION