What This Air Spring Does
This is a reversible-sleeve bag, not a convoluted bellows. The rubber sleeve rolls down over a 10.25 in. composite/aluminum piston as the axle moves up, which gives a soft, near-constant spring rate through the stroke. That is why it carries drive-axle load and still rides clean when the trailer is empty.
Working numbers: roughly 14 in. design height, about 20.75 in. fully extended and about 7.9 in. collapsed, with a 12.6 in. maximum outside diameter. Check your frame and axle clearance against that max O.D. before you order, especially if a previous repair swapped in something that was never the original bag.
Mounting is the standard drive-axle pattern. The top plate uses 3/8-16 blind nuts with a 1/4 or 3/4 NPT air inlet, and the bottom locates on the piston stud base. It bolts to the factory Hendrickson-style primary suspension without brackets or spacers when the original bag was the same family.
Why These Numbers Cross
Firestone builds this bag as the 1T15M-6, and the complete assembly with plate and piston carries W01-358-9211. W01-681-9084 is the number stamped on the service part most fleets order. Same sleeve, same piston diameter, same design height, same mounting hardware — the numbers differ because they describe the bare bellows versus the finished assembly versus the service pack.
Goodyear 1R12-092, Triangle 8512 and 6363, Phoenix 1DK23K-9211, and Granning 2692/15690 are competitor numbers for the same reversible-sleeve envelope. Each maker uses its own catalog logic, but the physical bag has to hit the same design height, stroke, and bolt pattern to be sold into the same suspension. That is what makes them interchange.
Navistar/IHC 501559C-1 is the truck-builder number for the same part on International applications. Those numbers are listed here for identification only. PartStop is not affiliated with, endorsed by, or authorized by any of these manufacturers, and none of these numbers imply a factory relationship.
Check Before You Order
Read the old bag first. The Firestone number is molded into the top plate or printed on the sleeve, and if it comes back 1T15M-6 or W01-358-9211, you are in the right family. If the printing is gone, measure design height at ride and measure the piston diameter. A cross-reference is a starting point, not a fitment promise — confirm by VIN or by the number on the part you pulled.
Check the air inlet size while you are under there. This spring takes 1/4 or 3/4 NPT at the top plate, and shops sometimes find an adapter fitting left in from an earlier repair. Note which one your line uses so you are not chasing a fitting after the truck is already on stands.
W01-681-9084 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to W01-681-9084. 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 |
|---|---|
| Firestone | W01-358-9211, 1T15M-6 |
| Goodyear | 1R12-092 |
| Granning | 2692/15690 |
| Navistar/IHC | 501559C-1 |
| Phoenix | 1DK23K-9211 |
| Triangle | 8512, 6363 |
Frequently asked questions
Is W01-681-9084 the same as W01-358-9211?
They describe the same drive-axle air spring. W01-358-9211 is the Firestone assembly number and 1T15M-6 is the bellows designation, while W01-681-9084 is the service number most often used when ordering. Physical dimensions, piston, and mount pattern match. Verify against the number on your old bag before ordering.
How do I know if my air bag is actually bad or it's just a leak somewhere else?
Air the truck up, shut it down, and spray the bag, the top plate, and the fitting with soapy water. Bubbles at the sleeve or a visible crack in the rubber means the bag is done. Bubbles only at the fitting usually means a bad NPT seal or a cracked line, not a failed spring. Also look for a piston that has been chewed up by debris, which will cut a new bag fast.
Do I need to replace both drive-axle bags at once?
Most shops do. The bags age together, and a single new bag next to a bag with years on it can leave the truck sitting unevenly and load one side harder. If one failed from a road hazard rather than age, replacing just that corner is reasonable. Check ride height on both sides after the job either way.
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Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
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