Why These Numbers Cross
This is a reversible sleeve, or rolling lobe, air spring for the drive axle position. The bellows rolls down over a piston instead of folding like a convoluted bag, which gives a softer, more consistent rate through the travel range. It carries the rear of the chassis on Hendrickson HAS series air suspensions found under Class 8 tractors and vocational trucks.
Dimensionally it runs about 7.6 inches compressed and 22 inches extended, with roughly 12.6 inches maximum diameter at the lobe. The top plate uses a two-hole stud pattern. The bottom is a single-stud piston with a 3/4-16 air inlet. Those four details — compressed height, extended height, stud pattern and inlet thread — are what actually decide whether a bag bolts in.
Failure is usually the sleeve, not the plates. Look for chafe marks where the lobe rubs the piston or a frame member, dry cracking on the sidewall, or a bead plate that has rusted through around the studs. A bag that leaks down overnight on one corner and sits the frame low is the classic symptom.
Why These Numbers Cross
Air springs get sold under a lot of numbers because the bag maker, the suspension maker and the truck builder each assign their own. The bellows itself is one design. Firestone catalogs it as W01-358-9373. Hendrickson, who builds the HAS suspension, puts it in their book as 57122-2 because that is what ships with the axle assembly.
Goodyear built the same envelope and listed it as 1R12-403, with 1S12-030 as the related listing. ContiTech carries AS9373 and Euclid lists FS9373 — both follow the 9373 suffix convention that traces back to the original Firestone designation. Triangle 8451 and Watson & Chalin AS-0127-G are the same bag under different catalog logic.
International 2992101C1 is a chassis-level number. When the truck was built with a Hendrickson HAS rear suspension, the truck maker assigned its own part number to the bag already installed. That is why a dealer counter number and a bag maker number both point at one piece of rubber. Numbers are listed for identification only.
These crosses are a starting point, not a fitment promise. Confirm by VIN or by reading the number off the plate on the old bag before you order.
Before You Order
Pull the old spring and read the bead plate. The number is usually stamped or on a foil label on the top plate. If the label is gone, measure ride height at the axle, then measure the stud spacing on the top plate and check the inlet thread. Compare against 7.6 in compressed and 22 in extended before committing.
Replace bags in pairs across the axle. A new spring next to a ten-year-old one changes load sharing and pulls the frame off level, which puts the height control valve into a constant correction cycle. While the bag is off, check the piston for rust scale and the shock for a wet body — a dead shock beats the new bellows apart.
W01-358-9373 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to W01-358-9373. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| ContiTech | AS9373 |
| Euclid | FS9373 |
| Goodyear | 1R12-403, 1S12-030 |
| Hendrickson | 57122-2 |
| International | 2992101C1 |
| Triangle | 8451 |
| Watson&Chalin | AS-0127-G |
Frequently asked questions
Is 57122-2 the same air spring as W01-358-9373?
They cross to the same rolling lobe drive axle bag. 57122-2 is the Hendrickson number for the spring fitted to HAS series suspensions, while W01-358-9373 is the bag maker's number. Listing both is for identification only. Verify against the number on your old part or by VIN before ordering.
How do I know if my air bag is leaking or the height valve is bad?
Air the system up, shut the truck down, and spray the bag and fittings with soapy water. Bubbles at the sleeve or bead plate mean the bag is done. If the bag holds but the frame still sits low or high on one side, look at the height control valve linkage and the valve exhaust port.
Do I need to replace both drive axle air springs at once?
Do it in pairs across the axle. Mixing a new spring with a worn one gives you uneven load sharing and a frame that will not sit level, which keeps the height control valve hunting. If the truck has high miles on all four bags, plan on doing the set while the suspension is open.
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