You may have a tag affixed to the top of your Goodyear air spring that shows the original part number, in this case 2B9-201. Unfortunately, this tag does wear away and may not be legible.
Newer Goodyear air springs have a plasticized tag affixed under the top plate that shows the original part number, in this case 1R12-432.
If neither of these is present, it is possible to locate your air spring by finding the Flex Member number and measuring the top plate and bottom plate/piston. The Goodyear Flex Member number is molded into the rubber, usually under the Goodyear logo. The number will be similar to "566-28-3-015." You can also locate the piston number that is stamped onto the bottom of the piston to help your search. This number is similar to the Flex Member number, ie "566-28-3-01."
With both these numbers, you will look up the Flex Member number in the Goodyear Air Spring catalog under Flex Member Index first. This will list all Goodyear Air Springs that use that Flex Member. Next, if you have the piston number, match it with the piston number. You will want to verify measurements in the next section before ordering since sometimes the same Flex Member and piston were used on different bags.
You are going to want to note: What fittings are on the top plate, distance between them and length and compare those with the part numbers from the catalog you identified as possible matches. You will also need to do the same with the bottom plate or piston. To measure max height you will want to stretch the bag as far as possible, without using air and measure from the top plate to the bottom of the bottom plate/piston. To measure minimum height, you will want to compress the bag as far as possible and measure from the same points.
If all else fails, you can always call the manufacturer of your truck or trailer and ask them. They will usually provide you with their OE number if asked, That number can be crossed to a suitable replacement air spring from Goodyear. If you have any other questions, give us a call at 800-435-3509.