Originally Posted by Eagle & Bear
Several months ago I posted photos of the broken frame on my Airstream. The characteristics of the crack indicated that it had occurred within the past several years. The photos showed that the forces that could have caused the crack were inconsistent with the prevailing theories on what causes Airstream frames to crack. I may have an answer for many of you who have had a frame break and we may be able to prevent frames from cracking in the future.
I bought my 1976 International 29’ rear bath before I knew much about vintage Airstreams. I did look at it very closely and consider myself very lucky that the Airstream that I bought was in good condition. Everything was original and, with the exception of the air conditioner, it all worked.
After reading about vintage Airstreams it became obvious that the 35 year old axles needed to be replaced. I took our Airstream to one of the vendors and had new axles put under it. Soon afterward I put on new shocks, backing plates and brake shoes and bought a new set of tires. We had traveled several thousand miles before I noticed that two of my tires had begun to wear unevenly. I sent photos of the tires to the vendor and he sent them to the manufacturer. The verdict was that the axles were out of alignment.
We traveled another 1000+ miles before we were able to find a shop that could align a straight axle. When I was growing up I had seen tire shops straighten the front axles on the older pickups using one set of chains to hold the frame in place and another set of chains to bend the axle back into alignment. The only shop in the region that could do an alignment on our Airstream used the chain method. The good news is that the alignment worked but the way the axles were realigned caused the frame to crack and may have damaged the torsion system as well.
While I was researching how to fix the broken frame I saw a photo of the axle straightening device that Airstream uses. It is a hydraulic unit that bends the axle housing but does not stress the frame. Since the hydraulic device is not readily available to most Airstream owners and the cost of traveling (I had to replace 3 of the new tires) can get very expensive, many have gone to local tire shops to align the axles. Unfortunately, most of the tire shops use the chain method. Vintage Airstream frames and axle mounting plates are way under built and have to be supported by the shell. They are not able to withstand the lateral forces imposed on them by the older alignment station methods.
Bottom line is that Airstream owners need to avoid the alignment stations that use chains to bend the axle by applying a counterforce to the frame and find a shop that uses a hydraulic tool similar to the one used by Airstream to do the job.
Your theory has some merit, but that is not the answer.
If you notice in the photo that clearly shows the crack, it's located right next to a weld.
The real cause of the cracking, is the inadequate amount of weld area between the frame and axle mounting plate.
The preventive fix, is to add additional welds between the frame and axle mounting plate so that there is no more and an inch or so, between the welds, and each weld should be at least 2 to 3 inches long.
This subject was discussed with Henschen some time ago, which concluded the inadequate amount of welds between the frame and axle mounting plates, was the cause of the frame cracking and/or the axle mounting plate warping.
It's unlikely that the same cracking would happen, if indeed the axles rubber rods were bad. In that case, damage to the shell would happen first.