Liftable Tag Axle Air Springs

[Fritz]

Those of you with liftable tag axle coaches may want to know what we learned in the process of replacing a leaking tag suspension air spring.

If you don't want to read all this, note that the appropriate Firestone replacement spring for a '97 liftable tag axle air spring is W01 358 9538, which has a bellows # 1T-15M-11 and internal bumper # 3159.

In response to a search for a new air bag, Earl Davis stated to the parts manager at Iron Horse RV in San Antonio (where we were having other repairs done) that replacements for the original bags were no longer available. I confirmed that with Chris Fogleman, who seemed at a loss for offering further assistance. Compounding the problem, I learned after calling Firestone, that they no longer make the original model (Firestone # W01-358-9369), though a substitute probably was available, but they couldn't help with the specific application. I was later told by Ben at Michigan Truck Spring (http://truckspring.com/) that he was told by Firestone the -9369 could be special ordered, but would take 4-6 weeks for manufacture. That wasn't a player for us. A phone search for a new air spring locally found one of similar external dimensions; but, as you will see, it was incorrect for the application. Meanwhile, I called Ridewell to see what they had to offer. The suspension air springs (as opposed to the ones which lift the tag axle) are known as "reversible sleeve" types and have compressed and extended dimensions of 9.70 and 27.60 inches, respectively. They aren't your typical double convolutes.

The original springs had two 1/2-inch mounting studs on 6.2" centers and an offset 3/4-inch pipe-threaded air line fitting on the bead plate. The bag ultimately recommended by Ridewell has a 1/2-inch mounting stud and a combo 3/4-inch shared air line/mounting stud on 5.5" centers. Therefore, the coach frame had to be drilled to accept the new spacing and stud size — one hole (forward): ok; the second (aft): newly drilled. Careful drilling will insure a positive new hole, since it's so close to the old hole. Ridewell said the slight change in airbag alignment geometry was insignificant to suspension action and either hole could be reused. However, moving the bag center aft by using the old forward 1/2" hole, increases clearance for torquing the top mounting nuts. (A nptm-to-quick release elbow, rather than the original compression fitting and new a "T", made airline replacement easy.)

Contributing to the problem of finding a suitable replacement bag was the knowledge that the bags were fed by 3/4-inch air lines. Logic led us to believe that (as with "kneeling" city bus) the larger air lines contributed to more rapid inflation and deflation during lifting/lowering of the tag axle. When I finally dipped into the "Blue Box" (ours is black) for suspension schematics, I discovered that the 3/4-inch lines to the bags come from a "T" which is fed by a 3/8-inch line (as are all other air springs on this BlueBird). It immediately became apparent that concern for finding an air spring with a 3/4-inch fitting was unnecessary. BlueBird probably used the spring they did because the rest of the bag's design was appropriate. Ridewell chose this substitute (Ridewell # 1003589538C; Firestone # W01 358 9538; $204 each from Ridewell) because the internal bumper is the correct size to allow bottoming of drive and tag suspension simultaneously (when on a level surface). The original and this replacement both use a #3159 internal bumper. Several other bags come close in dimensions, but aren't identical with the original. For spring particulars: http://www.firestoneindustrial.com/n...a/aftermarket/ (select the interactive catalog and search by bag number)

Once the correct replacement was found and delivered, installation was reasonably straight forward, though not something you'd do on the side of the road. Plan ahead. If you haven't changed airbags yet, you or a future owner will. This might help.

Fritz Washburn
Cocoa Beach, Fla.
'97 43' Mid-door

[iamflagman]

Thanks Fritz,

This would be a good one for those owners that might need this, to print out and place in their BLUE/BLACK BOX for future reference. I like all of the details, as that will explain things in the future for the next member that has this problem, again good job!!

To print out a copy, click on Thread Tools above the post then choose Show Printable Version then use your browser tools to do the rest.

[Randy Dupree]

Fritz,its post like the one you made that make this site so valuble.
This is very good information.
Thanks.
Randy

[JackandLiz]

Howdy, Fritz.
Thank you for posting this very detailed information on liftable tag axle air springs.



Regards,
Liz Pearce