Underbelly skin failure

[trvler]

I just got back from a 9,000km trip across the continent. Somewhere in the middle of the plains after hours of undulations on the concrete road of I-80 I noticed I was dragging a large sheet of thin-gauge aluminum underbelly. It seems that many of the rivets holding this aluminum underbelly had failed by metal fatique around the perimeter of the head of the rivet (probably by excessive flexion due to the bad road). Has anyone else had this problem? And any ideas how I might fix it? I just drilled a bunch more holes and screwed the sheeting down on the road, and that held OK until home.

I searched this site, and couldn't find any other references, which I found surprising as this is my second AS, and the first had similar problems with the underbelly skin.

Thanks

Paul

[SteveH]

Common problem because of the grade and gage of the aluminum Airstream uses on the belly pan.

I've drilled out a lot of the rivets and re-riveted with some heavier gage aluminum washers I've made.

[Landrum]

Is this really a common issue. That's not sarcasm....I've just never seen this issue come up before on AF. Maybe a lost rivet or two, but not loosing a whole piece of the belly pan. I guess I better add this to my list of things to watch.


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[SteveH]

Originally Posted by Landrum

Is this really a common issue. That's not sarcasm....I've just never seen this issue come up before on AF. Maybe a lost rivet or two, but not loosing a whole piece of the belly pan. I guess I better add this to my list of things to watch.


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I think it is common as I've had the problem on a couple of trailers. I suspect the more you tow, and the faster you tow, the rougher the road, the greater the problem.

[paiceman]

Happens more than you would imagine, with a lot of folks if it does not fall down and drag as yours did they never know it. Also, in addition to roads a still suspension on the TV can exacerbate the problem. We have not towed much at all with our F350, but will this summer and fall and will not be surprised if we have some rivet issues.

[Silverflames]

Push the belly pan back into place, drill new holes and used large head alum rivets. Ready to get dirty?

http://airstreamsupply.com/New-Airst...product_id=286

[Nomad518]

Same thing happened on our AS last summer. I replaced all of the rivets holding our belly pan in place with new rivets and used large washers between the rivet heads and the belly pan sheeting. The washers provide a much larger surface area to hold the belly pan in place than the rivets do on their own. It was a pretty easy job. Just make sure to wear safety eye glasses to prevent metal shavings from getting in your eyes when you are drilling out the old rivets and installing new ones. I got my replacement rivets and the washers at Home Depot.

[perryg114]

The problem is corrosion between the steel and aluminum. On older trailers you will find a hole corroded where the rivet head was. I drilled and tapped 1/4-20 holes in the frame and put in stainless bolts and zinc plated washers. On the cross members you can use super hard self drilling stainless steel sheet metal screws with washers but you still need to drill a pilot hole. I hate rivets for anything that I might have to get back into later. Never hurts to put antisieze (sp) on the bolts and screws. You can also get stainless steel rivets but I am not sure that will help with the corrosion issues.

Perry

[cwf]

you 'can' use the old holes... clean drill then rivet an aluminum 'strip' left to right (curb to street) to spread out the 'load' on the edge of the sheets... or use the larger 'aluminum' rivets Steve mentioned...

I would also have an immediate hard look at my running gear. It sounds like out of balance wheel/tires, towing too fast, too much WD, imbalanced load causing more 'flex' than normal in the chassis (see the movie 'The Long Long Trailer'),...

Those cracks in the aluminum certainly are 'fatigue' cracks from what I can tell.. and not 'good news'... nor should you 'ignore' or 'patch'.... look deeper... something's not right... IMHO.

[idroba]

You have not lived until you are on a major cross country trip and your belly pan decides to come off on the Ohio Turnpike (the '74 Argosy). I had to make field repairs with an underpowered cordless drill for some new rivets and vice grips to hold in place the really bad parts! All while huge trucks are going past at 70 mph and I was on the shoulder. Better repairs were made at the "campgrounds" that both Ohio and Indiana have at some of their rest areas. Still not fun with limited tools and resources.

Yes, it is a common problem. Corrosion, vibration, fatigue of the metal. At least it does not have to look pretty when done, just functional.

[perryg114]

You can also get a square of sheet metal, maybe 2x2" and use that as a washer when you put in a new rivet. I carry rivet tools and a drill ALL OF THE TIME. I have used them more than once.

Perry

[trvler]

Thanks for all the suggestions. I doubt it has anything specifically to do with my running gear (new rims/Michelin LT tires all balanced, and have Centramatics), but I'm using a Hensley hitch. The concrete roads of the I-80 have a repetitive undulation when the slabs get out of alignment which seems to set up a "bounce" like a standing wave with my TV and AS. It doesn't seem to matter what speed I go, just the bounce gets faster or slower. Very hard on everything (and passengers) and goes on for 100's of miles. I took the I-70 back which was smooth as glass in comparison. Anyone else have this experience on concrete roads? Roads around Winnipeg have been terrible for the same reason for years - at last they seem to be replacing them.

[airdreamers]

Did you ever hear of rivnuts. They are great for this kind of fix. You are able to rivet in to anything and have a female threaded nut ready to accept a screw with washer etc. Since learning about them from a friend, I have used them in a variety of ways, so will you if you decide to use them yourselves. I will attempt to attach 2 pictures of the tool and the rivnut, comes in different sizes. Available online or at HARBOR FREIGHT, (WHO WOULD HAVE THOUGHT!). No, I do not have stock in the company.

[trvler]

Has anyone used polypropelene or some other plastic to replace the aluminum sheeting on the underbelly?

[perryg114]

Plastic will sag and eventually age and crack. I suppose some sort of rigid fiberglass board could be used but that adds cost and weight.

Perry

[r carl]

Keep an eye out for broken rivets and replace as they fail.

[dwightdi]

The basic under engineered problem is that Airstream decided to attach the aluminum under skin directly to the steel frame without providing an electrical isolation. The resultant galvanic couple causes the aluminum to sacrifice itself to protect the steel frame when exposed to water or salt water from the road. There is no 100% solution to this problem, but you can extend the life of the trailer by using a thicker aluminum patch over the area that has corroded and replacing the aluminum rivets with stainless steel self taping bolts. I did it to my 1963 with good success.

[perryg114]

Try something like this with a pilot hole for the thicker steel of the frame. A big Zinc plated fender washer would be good as well.

McMaster-Carr

Perry

[PaulnGina]

Originally Posted by perryg114

Try something like this with a pilot hole for the thicker steel of the frame. A big Zinc plated fender washer would be good as well.

McMaster-Carr

Perry

That's exactly what I've used on the belly of our Avion. Works well.

[Silverflames]

Originally Posted by PaulnGina

That's exactly what I've used on the belly of our Avion. Works well.

Did you put thread lock on them?