What This Air Spring Is
This is a rear drive-axle air spring with a reversible sleeve and a plastic piston. The sleeve rolls down over the piston as the axle moves, so the effective diameter stays consistent through travel. That is what gives a loaded Class 8 tractor a stable ride height instead of a bag that stiffens up hard at the top of its stroke.
Published dimensions are roughly 17.7 in extended and 6.5 in collapsed, with a 9.5 in maximum diameter and a 1/2 in NPT air port. Those four numbers are what you measure against the old bag. If your collapsed height or port thread does not match, you are looking at a different suspension or a different position on the chassis.
Application is Kenworth conventionals running AG380 Airglide rear suspension and Peterbilt tractors running Flex Air rear suspension. This is a drive-axle part only. Do not order it for a trailer bogie, a steer-axle cab bag, or a lift-axle bag just because the diameter looks close in a photo.
Why These Numbers Cross
W01-358-8813 is the design number most shops key on, and the rest of the list describes the same physical assembly built or catalogued by a different supplier. Goodyear lists 1R12-069 and 1R12-669 against it, ContiTech uses 9 10-14 P 577, Automann uses 1DK23I-8813, Torque uses TR8813, and Triangle uses AS-8577. Same bellows profile, same piston, same port.
The truck-maker numbers are the ones you will find on a dealer invoice or in a chassis parts book. Kenworth catalogues this bag as C81-1012 and Peterbilt as C81-6000. Those are service part numbers assigned to a bought-in component, which is why one physical air spring carries two different chassis numbers depending on whose badge is on the hood.
Because everything in that list shares the extended and collapsed heights, the max diameter, and the 1/2 in NPT air port, they interchange as a bare bag. What does not automatically cross is the mounting hardware on your specific chassis — stud spacing, bead plate, and lower attachment vary. Confirm those against the old part before you pull the truck into the bay.
Failure Signs And Pre-Order Checks
Air springs fail three ways. The sleeve chafes through where it rolls, usually from road debris packed between bag and piston or from a bag running against a frame rail after a bushing sagged. The bead seal leaks at the plate, which shows as a slow overnight droop on one corner. Or the piston cracks, which you find by hand once the bag is off.
Before ordering, deflate the system, get under the truck, and read the number molded or stamped on the old bag. Match it to the list above. Check the port thread and count the mounting studs. Cross-reference is a starting point, not a fitment promise — confirm by VIN or by the number on the part you removed. Replace both bags on an axle so ride height stays even.
W01-358-8813 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to W01-358-8813. 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 |
|---|---|
| Automann | 1DK23I-8813 |
| ContiTech | 9 10-14 P 577 |
| Goodyear | 1R12-069, 1R12-669 |
| Kenworth | C81-1012 |
| Peterbilt | C81-6000 |
| Torque | TR8813 |
| Triangle | AS-8577 |
Frequently asked questions
Do I have to replace both air springs on the axle?
It is the normal shop practice. A new bag and an old bag on the same axle age at different rates and can hold slightly different heights under load. If one failed from chafe or a rubbed frame rail, inspect the other side for the same wear before you decide. At minimum, check ride height on both corners after the repair.
Is this the same bag as the Kenworth C81-1012 and Peterbilt C81-6000?
Those are the chassis-book service numbers for the same physical air spring, listed here for identification only. PartStop is not affiliated with or authorised by either truck maker. This is an aftermarket direct replacement. Verify against the number on your old bag or by VIN before ordering.
How do I tell a leaking air spring from a leaking height control valve?
Air the system up, shut the truck down, and spray soapy water on the bag seams, the bead plate, and the 1/2 in NPT port. Bubbles at the sleeve or plate mean the bag. If the bag is dry but the corner still drops overnight, work back to the height control valve and the supply line fittings.
Not sure it fits? We check before you pay.
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.
More cross-reference guides
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Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.