Air Spring Failure on Trucks and Trailers: Symptoms, Causes and How to Order a Replacement
A leaking air spring rarely fails without warning. Learn the signs, the usual causes and the details a supplier needs to quote the right part.
Air springs carry the load on most modern trucks, trailers and buses. They are simple parts, a rubber bellow between a top plate and a piston, but a failed one takes a vehicle off the road. The good news is that they usually give notice.
Symptoms to watch for
- The vehicle leans to one side or sits low at one corner after parking overnight.
- The compressor runs more often than usual, because the system is constantly topping up a leak.
- Visible cracks in the rubber, especially in the fold where the bellow rolls over the piston.
- A hissing sound near an axle with the engine off and the system charged.
- Uneven tyre wear or a harsher ride on one axle.
What usually causes the failure
Age and ozone. Rubber hardens over time. Fine cracks appear first on the rolling fold.
Abrasion. A bellow that rubs on a loose brake line, a bracket or debris wears through locally. Look for a polished or scuffed stripe.
Running at the wrong height. A faulty or badly adjusted levelling valve keeps the bellow over-extended or compressed. Over-extension can tear the bellow from the bead plate.
Worn shock absorbers. The shock absorber limits the extension of the suspension. When it is worn, the air spring takes loads it was not designed for.
Corroded piston or plate. Rust on a steel piston creates a rough surface that damages the rubber as it rolls.
What a supplier needs to quote
Air springs look alike and differ in details. Send as many of these as you can:
- The number on the bellow or the plate. This may be the air spring maker’s own number or the OE number of the vehicle or axle maker.
- Vehicle or axle make and model, for example a tractor unit model or a trailer axle from BPW, SAF or another axle maker.
- Complete unit or service bellow.
- Piston material: steel, aluminium or plastic.
- Position: axle number, and for buses front or rear.
When you fit the new one
- Replace corroded fixing hardware.
- Check the levelling valve and the shock absorbers on the same axle.
- Make sure nothing can touch the bellow through its full travel.
- Never inflate an air spring that is not installed and restrained.
Browse air springs and suspension parts on Bulapp, or send the number from your old part in a quote request.
Quick answers
Can I replace only one air spring on an axle?
It is possible, but if the other side is the same age it is usually close to the end of its life as well. Many workshops replace both sides of an axle together.
What is the difference between a complete air spring and a service bellow?
A complete air spring comes with the piston and top plate assembled. A service bellow is the rubber part only and reuses the existing metal parts.
How long does an air spring last?
Service life depends on load, road conditions, climate and maintenance, so there is no fixed figure. Regular visual inspection is more useful than a mileage rule.
Looking for a part?
Search by OE number or send your list for a quotation.
