What This Air Spring Is
This is a rolling lobe, or reversible sleeve, primary air spring for the trailer suspension. The bellows style is 1T17CA-6.5. Extended height is 21.5 inches, compressed height is 9.1 inches, and the assembly weighs roughly 14.8 pounds. It carries the trailer at ride height and does the damping work alongside the shocks.
Position matters here. This is a primary suspension bag on the trailer, not a cab air spring and not a tractor part. If the number on your old bag came off a truck seat or a tractor rear suspension, you are on the wrong page. Hendrickson identifies the same spring in the VANTRAAX HKA-200 as S-21966 and C-21966.
The rolling lobe design means the bellows rolls down the piston as the axle travels up. That rolling surface is what wears. It does not fold like a convoluted bag, so debris packed between the sleeve and piston is a real failure path, not a cosmetic issue.
Why These Numbers Cross
W01-358-8708 is the Firestone assembly number and 1T17CA-6.5 is the bellows style designation stamped into the same rubber. They describe one physical part: same bellows construction, same extended and compressed heights, same mounting arrangement. Hendrickson lists it under S-21966 and C-21966 because Hendrickson buys the spring in and puts its own number on the box for the VANTRAAX HKA-200.
The remaining numbers are the same story from other suppliers and OEMs who spec the HKA-200. Goodyear catalogs it as 1R13-128, ContiTech as 64638, Navistar as 1R13-250, Triangle as AS-8526, and Neway as G2298708300. These are listed for identification only. PartStop is not affiliated with, endorsed by, or authorised by any of these manufacturers.
Because the numbers all trace back to one bellows and one set of end fittings, any of them showing on your old bag points to this replacement. A cross-reference is a starting point, though, not a fitment guarantee. Confirm by the number printed on the part you are pulling, or by VIN and suspension tag.
How These Bags Fail
Most failures are wear-through on the rolling surface. Road grit, a curled mud flap, or a loose brake hose rubbing the sleeve will open a pinhole that grows fast. You will hear it as a constant hiss with the trailer parked and charged, and the trailer will sit low on one corner overnight.
Check the piston before you install the new bag. A cracked or corroded piston chews the new sleeve in weeks. Look at ride height too. A bag running outside its designed travel because the height control valve linkage is bent or the leveling valve is stuck will fail early no matter what you install. Verify suspension model, mounting style and ride height before ordering.
W01-358-8708 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to W01-358-8708. 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 | 64638 |
| Firestone | 1T17CA-6.5 |
| Goodyear | 1R13-128 |
| Hendrickson | S-21966, C-21966 |
| Navistar | 1R13-250 |
| Neway | G2298708300 |
| Triangle | AS-8526 |
Frequently asked questions
Is 1T17CA-6.5 the same as W01-358-8708?
Yes, they refer to the same air spring. 1T17CA-6.5 is the bellows style designation, W01-358-8708 is the full assembly number. If either one is legible on your old bag, this aftermarket spring is the match. Confirm the mounting hardware on the part you remove before you order.
Will this fit a Hendrickson VANTRAAX HKA-200?
It is built as a direct replacement for that suspension, which Hendrickson catalogs as S-21966 and C-21966. That said, VANTRAAX suspensions were built in variants, so cross-reference alone does not confirm fit. Check the number on the bag you are pulling or verify by VIN before ordering.
Should I replace both bags on the axle at once?
Most shops do. A new bag next to a bag with several hundred thousand miles on it gives you uneven ride height and puts the older one closer to a roadside failure. At minimum, inspect the mate for rolling-surface wear, dry rot and piston corrosion while the trailer is already lifted.
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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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