Zero Maintenance Damping Suspension Servicing

Zero Maintenance Damping Suspensions servicing

It is important to understand how Zero Maintenance Damping Suspensions servicing works and how to conduct a service inspection, like most systems on trucks and trailers.

Suspensions that use Hendrickson Zero Maintenance Damping (ZMD) air springs don’t have the same service inspection requirements as standard shocked suspensions. The main difference with these suspensions is that there are no shock absorbers, which ultimately fail or leak.


The ZMD suspension system eliminates the need for conventional shock absorbers and integrates the damping function into the air spring. ZMD air springs have an air chamber built into the lower air spring piston. 

Zero Maintenance Damping Suspensions servicing

The air spring chambers exchange air through calibrated orifices in the top of the piston. When the suspension hits a bump in the road, the piston moves up into the bellows, air in the bellows pressurises and moves through the orifices into the piston chamber. The orifices in the piston restrict air flow in the same way as oil flow is restricted by traditional shock absorber piston valves.

On rebound, the bellows area increases in volume and the air in the piston chamber moves through the orifices back to inside the bellows. This action provides controlled suspension movement that delivers good ride quality, eliminating the need for shock absorbers.

Zero Maintenance Damping Suspensions servicing

However, one function air springs are not able to achieve is rebound limiting. Therefore, to prevent excessive axle rebound movement ZMD suspensions use down stop chains.

Hendrickson ZMD suspensions rely primarily on the air spring for suspension control. Therefore, correct ride height, cleaning and inspection of these air springs plays a critical role in suspension reliability. 

IMPORTANT:  The specialised ZMD air springs cannot simply be interchanged with standard air springs. 


Ensure that mounting hardware, air springs, spacers and down stop chains are in good condition and correct for the designed suspension ride height. Any worn, damaged or mismatched parts may result in damage to the suspension and suspension components.

Look for chafing or any signs of component damage. Look for misplaced air lines that may rub on air spring bellows. Check to ensure truck or trailer ride height is at specification. Operating at an incorrect ride height will place extra strain on air springs and other suspension components.

Ensure that the upper bead plate is tight against the mounting bracket and that the mountings show no sign of movement. Air springs should be cleaned regularly of dirt and dust that may build up around the bead. Any grime in this area will eventually wear through the rubber bellows and cause premature failure to occur.

ZMD Service FAQ

How can I identify a ZMD suspension?

The main sign will be that instead of shock absorbers, there will be chain down stops. There may also be a label on the trailer chassis indicating fitment of a ZMD shockless suspensions. Closer inspection will reveal the words Zero Maintenance Damping embossed above the unique ZMD part number on the air spring bellows. See image above.

How do I confirm the damping on a ZMD suspension is correct since there are no shock absorbers to check?

There are no moving internal components in a ZMD air spiring. So, there are no inner parts that will wear out or fail. If the suspension is fitted with the right air springs, that are in working order, then it will be correctly damped.

To find out more about Zero Maintenance Damping Suspensions servicing from Hendrickson, click here.

Zero Maintenance Damping Suspensions servicing

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