1980s Airstream motorhomes were built on a Chevy P30 chassis. To support the weight of the motorhome and make the ride more comfortable, Airstream installed an air suspension system in the back. It is prominently featured in this old Airstream commercial, converted from VHS tape. On our way from CA to IL, our airbags failed. Here’s what happened, what we learned, and how we fixed it.
American Carrier System (ACS) Superide 815 Air Suspension
The air suspension system is made by American Carrier System, a company based in Fresno, CA. Luckily for us, key parts of this system are still available today, 40 years later, and can be ordered directly from the company (phone number: (559) 441-1460). Here are some useful diagrams of the system:
This is what it is supposed to look like when everything is working fine:
Note how the spring beam is horizontal to the floor. The two airbags are perfectly vertical and rest on the spring beam, with the transverse rod mechanism in the middle.
The Problems
Halfway between CA and IL, we noticed that our airbags had broken. After further investigation, we discovered that the airbags, one of which was just recently replaced (why only replace one, you have to wonder?), were of the wrong type, and had been mounted in the wrong way:
- The correct airbag for this system is the Firestone 5412. It contains a bumper designed to prevent significant damage to the vehicle or suspension in the event of a sudden loss of air pressure in the spring. Unfortunately, the wrong part was installed (Automann 5505), and to make matters worse, that part doesn’t have the internal bumper.
- As can be seen from the drawings above, the airbags are attached at the bottom with a 1/2-13 Grade 8 rod. Instead, ours were attached with a bolt.
As a result, the airbags didn’t last long. They ripped out of the spring beam and caused damage all around. The bolts were bent, the spring beam was no longer horizontal but slanted, and the leaf springs were all the way up pushing against the frame (because of lack of airbag bumper). Upon further investigation, the bushings, straddle pins, and the transverse rod were all damaged because of the tremendous forces acting on them in the absence of working airbags. This is probably what caused the spring beam to be slanted. The holes in the spring beam through which the airbags attached were also damaged when the bolt ripped through it.
The Fixes
Needless to say, some serious damage, and not ideal in the middle of a road trip. Luckily we found a truck service center in Champaign, IL who was willing to help, a very active classic Airstream motorhome community on Airforums who helped with troubleshooting and overall guidance, and good support from ACS to confirm the issues, identify the right parts and ship them out immediately.
To make repairs more difficult, the location of the airbags is very challenging. In order to get access to them, you need to lift up the frame and remove all weight from the spring beam. In addition, there is very little room between the crossmember and the inside floor where the top of the airbags are installed. It took the service center 2 full days to get the old airbags out and install the top part of the new airbags. It would have been faster to cut open the floor to get access to that space.
After installing the top part of the airbags, we removed the spring beam, replaced the spring beam bushings and bolts (swap the direction of the bolts when reinstalling!) and replaced all key components of the transverse rod mechanism (bushings, bolts, transverse rod, and straddle pins).
Finally, we fabricated two plates and welded them to the spring beam to fix the holes that were damaged while at the same time improving the support for the base of the airbags. The full base can now rest on a plate, instead of just on the beam itself.
New Parts List
- 2x Firestone 5412 Airbags
- 4x Transverse rod bushing (7572-102)
- 2x straddle pin (5506-001)
- 2x spring beam bushing (5503-023)
- 1x Transverse rod (5001-004)
- 1x Fully threaded rod, Grade B7
+ various small parts such as bolts, nuts and washers (all grade B7).
Next Steps
The airbag and mechanical parts are only half the system. The second half is the air pressure part, which includes leveling valves, air tank, compressor, etc. More to come on that topic.