Proper maintenance extends outstanding durability of air bag equipped vehicles on mining and construction sites

Firestone air springs have set quality benchmarks since the company invented the air spring in 1938

Air springs used in modern vehicle suspensions throughout Australia are so tough that they will often outlast other maintenance items such as bushings, shocks, levelling valves or regulators.

Big rigs as used by mining, construction and civil engineering companies, as well as semi-trailers and road trains with gross vehicle masses (GVMs) exceeding 100 tonnes, ride on the same basic type of robustly engineered rubber-and-fabric air bags that are also used on 4wds, work vehicles, contractor and towing vehicles also involved with such sites.

All benefit not only from reduced maintenance and smoother, more comfortable ride compared with older steel spring types, but also they achieve easily adjustable load height (by releasing or adding air) and enhanced safety through better steering and braking resulting from stable, level vehicles, both front-to-rear and side-to-side.

“Airide™ springs by Firestone are so tough they are warranted to be free of material defects and/or workmanship for 3 years or 300,000 miles (480,000 kms) whichever occurs first. But in service they frequently attain hundreds of thousands of kilometres above their expected service life,” says Air Springs Supply Pty Ltd, national distributor of Firestone Industrial products.

Firestone manufactures the world’s No 1 selling air Springs. More suspension builders use Firestone Airide™ air springs than any other brand. Firestone Industrial Products Company offers a complete line of Airide springs, with replacement springs available for virtually every vehicular air suspension system as well as the industrial versions of the same type of airbags used found on conveying, material handling, concrete form production equipment and sorting applications in the resources and engineering industries.

Rolling sleeve (left) and convoluted Air Springs (right) are used in applications extending from semi-trailers to 4WD and contractor vehicles

“Since each individual air spring is closely examined and pressure tested at the factory, 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 Air Springs Supply Sales Manager Mr Russell Chown. “Before you install a new air spring, you should carefully examine the old one to see what caused it to fail. If it was due to a defect in the suspension system, then the new air spring may also fail unless you correct the problem” he says. Common issues include:

BOTTOMING OUT. Indications of this problem include concave bead plate, internal bumper loose, hole in girdle hoop area (convoluted), hole in bead plate junction area or leaking around the blind nuts. Possible causes of the problems include broken or defective shock absorber; defective levelling valve; overloaded vehicle; pressure regulator set too low; wrong air spring (too tall).

ABRASION. Indications include hole rubbed into the side of the bellow or hole in the bellows area where it rolls over the piston of reversible sleeve style air springs. Possible causes included structural interference, such as broken shock absorber, loose air line, misalignment and worn bushings. Further possible causes include no air pressure (reversible sleeve style), foreign material (including rocks and sand from worksites) and wrong air spring.

MISALIGNMENT. Indications include off-centre bumper contact and similar symptoms to ABRASION AND BOTTOMING OUT. Possible causes include worn bushings and improper suspension installation.

LOOSE GIRDLE HOOP. indications include rubber bellows distorted and girdle hoop torn loose. Possible causes include running at extended positions with low air pressure.

CIRCUMFERENTIAL CUTS. Indications include bellows cut in circle at bead plate junction or (in the case of reversible sleeve type) at piston junction. Possible causes include high pressure and full extension for extended periods, or impact in compressed piston.

OVER-EXTENSION. Indications include bead plate convex, especially around blind nuts or studs; bellows separated from bead plate; leaks at blind nuts or studs; leaking at end enclosure (reversible sleeve); loose girdle hoop on convoluted style. Possible causes include broker or wrong shock absorber; defective levelling valve; ride position too high; defective upper stop or wrong air spring (too short).

Preventative Maintenance

To prevent failures such as those above, and to optimise the excellent lifespan of Airide springs, some simple routine checks will pay handsome dividends:

1. Where are air springs found? Air springs can be found at a number of locations on the truck and trailer, including the primary suspension springs for the truck and trailer, auxiliary axles (such as a lift axle), as well as the cab suspension and often a front (steering axle) suspension. It is important to take note of all your air spring locations so that all of the locations receive proper maintenance.
2. How often should I inspect my air springs? This depends somewhat on usage of the vehicle or trailer. The inspection could be based on frequency (such as quarterly or bi-annually), mileage (such as 80,000km 50,000 miles) or in conjunction with other suspension maintenance activities.
3. What should I look for when I inspect my air springs? During your routine inspection of Firestone air springs take special note of any debris, cuts, deformities, or rubs that may lead to an imminent failure. If the air spring is damaged, replace it during this visual inspection process. If the air spring is damaged there is also a high probability that there may be other problems with the suspension, or other damaged components.
4. Do air springs ever need to be cleaned? Once per year, when performing a thorough inspection, it is advised to clean the air spring with a soapy water or alcohol solution. This will help expose problems hidden from normal visual inspection. Soap bubbles may also help identify slow leaks that could be occurring, indicating a failing air spring. Do not expose air springs to open flames, solvents or abrasives or else you may unintentionally damage the air spring, particularly the rubber. APPROVED: soap and water, methyl alcohol, ethyl alcohol and isopropyl alcohol. NON-APPROVED: all organic solvents, open flames, abrasives and direct pressurized steam cleaning
5. Can I use an impact wrench to install my air bags? It is advised that an impact wrench is not used to install Firestone air bags. An impact wrench increases the danger of stripping the fittings off the bead plate. A torque table showing the installation force on various sizes of fasteners is available via a sticker on top of every new part and in our catalogues. It is important to follow these guidelines and use torque wrenches to achieve these recommended tightness values. It is important to check the tightness of all mounting hardware (nuts and bolts), if loose re-torque to manufacturer’s specifications-do not over tighten

Inspection priorities

1. Inspect the O.D. (Outside Diameter) of the air spring. Check for signs of irregular wear or heat cracking.
2. Inspect air lines to make sure contact doesn’t exist between the air line and the O.D. of the air spring. Air lines can rub a hole in an air spring quickly.
3. Check to see that there is sufficient clearance around the complete circumference of the air spring while at its maximum diameter.
4. Inspect the O.D. of the piston for build-up of foreign materials. (On a reversible sleeve style air spring, the piston is the bottom component of the air spring.)
5. Correct ride height should be maintained. All vehicles with air springs have a specified ride height established by the O.E.M. manufacturer. This height, which is found in your service manual, should be maintained within 6-7mm (1/4”). This dimension can be checked with the vehicle loaded or empty.
6. Levelling valves (or height control valves) play a large part in ensuring that the total air spring system works as required. Clean, inspect and replace, if necessary.
7. Make sure you have the proper shock absorbers and check for leaking hydraulic oil and worn or broken end connectors. If a broken shock is found, replace it immediately. The shock absorber will normally limit the rebound of an air spring and keep it from overextending.