Over-extension

 

It results from unrestrained downward travel of the axle that forces the air spring to consistently operate beyond its maximum extended height.  The first sign of damage on an over-extended air spring usually is the bellow separating from the metal top plate or at the piston.

Air spring failures resulting from over-extension are most commonly seen on lift axle applications and par-particularly on trucks or tractors used in severe on/off road service such as construction, logging or quarrying.

On those types of vehicles, check to see if the shock absorbers need to be repaired, replaced or are missing - not an unusual occurrence.  Although shocks were not designed as axle travel limiting devices, they are often the only defense against over-extension.

Solution:
Bring the air spring back into the proper operating zone by: limiting axle travel, checking leveling valve for proper operation, adjusting leveling valve to proper ride height and checking for proper application. 

PHOTO: Over-extension of the air spring results from unrestrained travel of the axle, which eventually tears the bellow away from the metal top plate or the bottom piston.
 

 

   

Normal cycle fatigue

 

Longitudinal fatigue cracks will appear in the outer surface of the rubber as part of the normal aging process.  They are created by the constant up and down cycling to which the bellow is subjected.

If an air suspension system is well-maintained, air springs will deliver long operating performance. Although, air springs are not often allowed to fatigue naturally.

Knowing what to look for and how to correct those problems can prove to be extremely productive for you, both in air suspension service/repair, and in gaining your customers’ confidence and business.

Solution: 
Know your limitations. Air springs can’t last forever.  Check for wear in your PM schedule, record expected life.  Replace before a failed spring strands you.

PHOTO: Normal cycle fatigue - which when compared to the other causes cited, occurs the least often. 

 

   

Damage from chemicals

 

Paradoxically, a prime substance that robs air springs of life is one that is applied to other vehicle components to sustain their smooth operating and life, and that is grease, especially when it is over-zealously applied.

Excessive grease applied to a universal joint can be slung off during rotation onto one or both of the air springs of the lead axle/air suspension configuration in a tandem setup.  Aggressive application of grease to a fifth wheel will have the same damaging affect on either of both of the rear air springs in a tandem setup.

Solution:
Periodically check condition of the air spring. Check for excessive oil or water in the air supply. Check seals, avoid excessive greasing, watch for content spillage. Check for debris build up at the piston, girdle hoops, bead plate. Keep them clean. Use soap and water - never a petroleum-based cleaner. 

PHOTO: Deterioration of the bellow - is caused by chemicals that, in time, literally eat a hole in the rubber 

 

   

Corrosian and impacts

 

As with any other metal part on a vehicle, the top plate of an air spring is subject to rust which ultimately will eat an air-escaping hole into it.  And, though pistons generally are made of corrosive-resistant aluminum or composite plastic material, they are subject to pitting from salt.

The pitting eventually will wear a hole (or holes) into the rubber bellow as it slides over the piston in its normal course of operation. Road debris also can be flung against the piston, causing it to crack.

Solution:
Periodically check condition of the air spring. Check for excessive oil or water in the air supply. Check seals, avoid excessive greasing, watch for content spillage. Check for debris build up at the piston, girdle hoops, bead plate. Keep them clean. Use soap and water - never a petroleum-based cleaner.

PHOTO: Deterioration of the top plate or piston - can be caused by chemicals, and/or the result of road debris. Both problems finally create premature failure. 

 

   

Abrasion

 

Abrasion of the rubber bellow can be caused in two ways:  Contact with other components on the vehicle, or with foreign objects.  In the first instance, more often than not, an air line that feeds the suspension or braking system is the culprit.  This usually occurs more often on tractors rather than on trailers because of the need to locate multiple lines in a more compact area.

Bellow abrasion also can be caused by simple road dirt and debris in over-the-road, linehaul applications.  Additionally, the potential for bellow abrasion is higher during the winter months when sand, gravel or salt is spread on roads to melt snow and ice and provide traction. Those substances will accumulate around the piston or bead plates of the air spring and eventually rub a hole in the bellow as it moves over the abrasive material in normal operation.

Abrasion damage to an air spring may be caused by another worn or failed parts in the air suspension system.  Worn bushings, for example, will throw an air spring out of its operating envelope.

A leak or pinch in the airline to the suspension system, if not fixed, eventually can cause under-inflation of the air spring and result in constant contact of the rubber bellow with an abrasive suspension part crating a hole over time.  This type of abrasive failure is more common in the rolling lobe style air spring.  In over-the-road applications, abrasive wear will take place on empty trailers or tractors “bob tailing,” since one axle can support the vehicle weight as the other axle “airs out.”  When one or more, but not all, air springs become under-inflated in the operation of a vehicle, the under-inflated springs have a tendency to deform, instead of rolling uniformly over the piston.

Solution:
Clear air spring of obstructions or contact by:  checking for proper air supply, securing all surrounding parts to eliminate contact with bellow, strap air supply lines away from the bellow, check for proper application.

PHOTO: Abrasion of the rubber bellow - is caused by an object constantly rubbing on it, ultimately creating a hole.