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Air Suspension

US Fleet Bus RepairsAir springs and electronic ride controls provide a cushy, boulevard ride, but the ride doesn’t last forever. All air suspensions share a common vulnerability: air leaks. And when a system can no longer hold air, it goes flat.

Air Ride Basics

With an air ride suspension, hollow, inflatable rubber bags (air springs) are used in place of ordinary coil steel springs or leaf springs. The rubber bags are flexible and have a certain amount of give, so they help absorb and dampen bumps to better isolate the suspension from the vehicle’s occupants. Air springs also provide a variable spring rate and offer increased stiffness the more they are compressed.

Air Ride Problems

Air suspension problems usually fall into one of these categories:

Electrical – Problems with the height sensors, air spring solenoids, module control circuit, compressor relay, compressor or vent solenoid. These can be isolated by using the system’s self-diagnostic procedures (if available) and various volt/ohm checks. Service consists of replacing the faulty component or wiring, or readjusting the height sensors.

Air supply – Leaky or obstructed air lines, faulty compressor or spring solenoids. Diagnosis is made via the self-test and visual inspection.

Air springs – Leaking, damaged, deflated or unfolded springs. Damaged springs must be replaced as an individual assembly (replacement in pairs is not necessary with air springs). If unfolded, the spring must be carefully inspected for cuts or cracks before it is reinflated.

Leveling Valves or ECAS – Standard leveling valves mechanically maintain enough pressure in the air springs to keep the vehicle at the appropriate height and need to be adjusted properly. Some vehicles use ECAS – or Electronically Controlled Air Suspension  - with ride height sensors relaying information to a computer that individually adjusts the pressure in each bag to reach the operators goal from a smooth ride, to lowered height for easier loading and unloaded, or even a raised ride to increase ground clearance for getting out of a tight spot.

Replace the Dryer

It is very important to ensure that the source of air for the compressor is clean and as dry as possible. When air is compressed, the water vapor contained in the air is condensed into a liquid. If there is no means of removing the water from the system, it will find its way to all parts of the system, causing corrosion damage or freezing.

Most systems have a dryer that is connected to the compressor outlet to absorb the water entering the system. The dryer contains a moisture-absorbing desiccant such as silica gel. The desiccant can hold a given amount of water and once it is saturated, it will allow water to pass into the system.

The dryers that are installed on most systems do not have an indicator that will show when it is saturated and no longer able to absorb water. An additional dryer with a moisture indicator can be added to the original equipment dryer. It can be installed in the supply line and placed in a position where a periodic check can be made.

Alignment

Ride height can also affect caster. A deflated air spring or defective ride height sensor can increase caster readings by up to a degree or more. Jacking up the front of a vehicle or dropping the nose will have the opposite effect and reduce caster readings. This may contribute to a steering problem, such as instability or poor steering return. That’s why ride height and the condition of the air suspension system should always be measured prior to checking wheel alignment.