Air Suspension Failures: Bags, Height Valves and Leaks

A truck sitting low on one corner, or riding hard, or leaning at a dock is telling you something about the air suspension. It matters beyond ride quality, because a suspension out of level puts uneven load on tires, on the frame and on the fifth wheel.

Here is what fails and what it looks like.

Air bags

Rubber bags fail from age, from chafing against something they should not touch, and from being run flat. A bag that has been operated collapsed will destroy itself against the frame or the axle.

Look for cracking on the rubber, wear marks where it contacts something, and obvious tears. A bag with a hole is a hole you can usually hear.

Height control valves

The height valve senses ride height and adds or dumps air to hold it. When it fails, the suspension sits too high, too low, or hunts constantly.

The linkage is the part that usually goes. A bent or disconnected linkage arm means the valve is reading a height that has nothing to do with reality. It is a cheap part and an easy check.

A valve stuck filling will run the suspension to full height and keep the compressor working. Stuck dumping means it never comes up.

Finding leaks

Air suspension leaks are usually audible with the engine off and the system charged. Work systematically — bags, fittings, lines, the height valve, and the connections at each.

Soapy water finds what you cannot hear. Small leaks matter because they run the compressor constantly, and a compressor running constantly runs hot and passes oil into the dryer.

Why a leaning truck is a real problem

• Uneven tire loading, which wears tires unevenly and generates heat on the loaded side
• Frame and suspension components carrying loads they were not designed for
• Fifth wheel height wrong, which affects trailer angle and load distribution
• Brake performance affected by weight transfer
• Ride harshness that beats up everything else on the truck

Do not run a truck with a collapsed bag any further than you have to. The bag destroys itself and whatever it is rubbing against, and the axle can end up on the frame.

Shocks matter here too

Air bags carry the load. Shocks control the movement. A truck with dead shocks bounces on its bags, which is hard on tires, on the bags themselves and on the driver.

Cupped tire wear is the usual sign, along with a truck that feels floaty or that keeps moving after a bump.

Trailer suspension

Everything above applies to trailer air suspension too, and trailers get inspected less. A trailer leaning at the dock or sitting low on one side has the same problems and nobody notices until a tire is destroyed.

Worth including in a walkaround: does the trailer sit level, are the bags intact, is the height valve linkage connected.

Manual dump valves

Plenty of drivers dump the suspension at a dock and forget to air it back up. Running down the road on dumped bags is hard on everything and it is easy to do without noticing on a truck that rides rough anyway.

Torque rods and bushings

Air bags get the attention because they fail visibly. Torque rods and their bushings hold axle alignment, and when the bushings wear, the axle moves under load. That shows up as odd tire wear, a truck that wanders, and a trailer that does not track straight.

Worn bushings are visible on inspection — play at the rod ends, cracked or missing rubber. It is a cheap part that causes expensive tire wear when ignored.

What to check in a walkaround

• Does the truck sit level side to side and front to back
• Are all bags inflated and free of visible damage or chafe marks
• Is the height valve linkage connected and straight
• Any audible leaks with the system charged
• Shock absorbers for leaks or damage
• U-bolts and fasteners for looseness
• Torque rod ends for play

That is a two-minute look and it catches most of what strands a truck or destroys a tire.

If your truck is sitting crooked, riding hard, or you can hear air going somewhere it should not, call (850) 495-0366. Dispatch answers 24 hours a day and James will come out with bags, fittings and lines and sort it where you sit.