What This Air Spring Does
This is a rolling lobe, or reversible sleeve, air spring with a composite piston. The rubber bellows rolls down over the piston as the trailer squats and rolls back up as it unloads. That rolling action is what gives a smooth ride under light load and still carries a full deck. It mounts on the trailer axle position of the suspension.
Working numbers on this unit: extended height 19.40 inches, compressed height 6.00 inches, and a design ride height window of 9.5 to 11.5 inches. Ride height is set by the height control valve linkage, not by the bag. If the bag is new and the trailer still sits low or high, the valve and linkage are your next stop.
Failures show up a few ways. Sidewall chafe from a loose or rotated bellows rubbing the frame or an air line. Piston cracks from running on the bumper after an air loss. Bead leaks at the top plate after a bag has been run soft for a while. Cords showing through the rubber means it is done, no patching it.
Why These Numbers Cross
W01-358-8709 is the Firestone catalogue number for this bellows and piston assembly. Hendrickson buys the same physical unit for its INTRAAX AA230 and Van Traax HKA-180 suspensions and lists it under its own service numbers S-21800, S-20900 and C-21800. Same bag, different label on the box, which is why a Hendrickson dealer ticket and a Firestone ticket can describe the same part.
Goodyear 1R13-159, ContiTech 64645 and Triangle 6390 are competing suppliers' numbers for an air spring with the same extended and compressed heights, the same top plate pattern and the same piston mounting. Navistar 1R13-249 is a truck OE part number applied to that same Goodyear-pattern spring for trailer and chassis service. Torque lists it as TR8709.
All of those numbers are printed here for identification only. PartStop is not affiliated with, endorsed by or authorised by Firestone, Hendrickson, Goodyear, ContiTech, Triangle, Navistar or Torque. A number match is where you start, not where you stop.
Check Before You Order
Pull the old bag and read it. The number is usually moulded or stamped on the top plate or printed on a label on the bellows. That number, or the suspension tag on the trailer, is what confirms fit. A cross-reference list is a starting point only, so verify against the part in your hand or against the trailer VIN before you commit.
Confirm the suspension model too. INTRAAX AA230 and Van Traax HKA-180 use this spring, but a trailer that has been rebuilt or had an axle swapped may not carry the suspension it left the factory with. Check the mounting: stud pattern and count on the top plate, air port location and thread, and how the piston bolts to the beam.
W01-358-8709 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to W01-358-8709. 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 | 64645 |
| Goodyear | 1R13-159 |
| Hendrickson | S-21800, S-20900, C-21800 |
| Navistar | 1R13-249 |
| Torque | TR8709 |
| Triangle | 6390 |
Frequently asked questions
Is Hendrickson S-21800 the same bag as W01-358-8709?
They are listed as the same air spring, with S-21800 being the Hendrickson service number and W01-358-8709 the Firestone number for the same assembly. S-20900 and C-21800 also appear against this bag. Confirm by reading the number off your old bag or by checking the suspension tag on the trailer before ordering.
Do I have to replace both air springs on the axle?
Not required, but it is common shop practice. A new bag next to an old, fatigued one can load the axle unevenly and put the trailer slightly off level. If the second bag is the same age and has similar chafe or weather cracking, do them together and save yourself a second trip under the trailer.
My trailer still sits low with a new air spring. What now?
Ride height on this suspension is controlled by the height control valve and its linkage, not by the bag itself. Design ride height is 9.5 to 11.5 inches. Check the linkage arm for bends or a loose clamp, check the valve for a leaking exhaust port, and check the air line to that bag for a restriction or a partial blockage.
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