Air suspension systems are designed to enhance suspension performance and maintain load equalisation among the axles at the designated ride height and for a workshop, it’s all about getting suspension ride height right.
Operating an air suspension outside of the specified ride height can reduce ride quality, damage cargo and increase suspension wear. To operate at optimal performance, each suspension (truck and/or trailer) must be set at its designated ride height.
Ride height specifications can differ greatly, this will depend on the suspension model, application, and requirements of the truck or trailer manufacturer.
Both truck and trailer ride heights are specified by the OEM. However, most trailer manufacturers will display the specified ride height on a label mounted to the trailer frame. To obtain the truck ride height, please check with the manufacturer for the correct specification.
Even though there are many varying methods, ride height is generally measured from the centre of the axle to the bottom the frame for truck and trailer.
Trailer ride height can be checked with the trailer coupled or uncoupled from the prime mover.
- If the trailer is uncoupled from the prime mover, apply shop air to the emergency glad hand to maintain pressure in the system. This will also ensure the trailer parking brake is released;
- If measuring the trailer coupled to the prime mover, ensure that the fifth wheel height is the same as the designated trailer kingpin height;
- If the prime mover fifth wheel height is different from the specified trailer kingpin height, then uncouple the trailer from the prime mover, set the height and make the measurement.
- Ride height that is out of specification should be corrected to prevent adverse effects and premature component failure to the suspension system. If ride height is lower than specified, it must be raised and vice versa.
Adjusting ride height can be achieved by performing the following:
- Disconnect the linkage from the height control valve extension arm;
- Rotate the extension arm up to raise or down to lower the axle;
- Adjust until the distance between the suspension mounting surface and the axle centre matches the recommended suspension ride height;
- Centre the control arm in the neutral position with a wooden centring dowel (a golf tee will do) through the alignment hole;
- Adjust the height control valve linkage as necessary and reattach it the extension arm.
- A delay of 5 to 10 seconds may occur before the height control valve allows air to or from the air springs;
- Linkage to the height control valve may differ between truck and trailer applications.