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Old 08-20-2014, 11:18 AM   #1
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floor connected to shell?

I asked about a rear bath and was told about potential sag, and i was talking to my 14 year old and he said how is the floor connected to the shell, and i had to say, "I don't know, but let me ask the experts."
So, how is the floor connected to the shell? is it riveted? the aluminum shell to the steel bottom frame? and also, could you tell me how to say these things correctly? :-)

Thank you.

Lisa
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Old 08-20-2014, 12:02 PM   #2
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The main connections are at the rear and front of the trailer. There are a series of bolts that go through something called a c-channel which is fastened to the bottom of the skin wall. Bolts go through the c-channel through the wood floor, sometimes through a steel hold down plate and then into the frame. There are a few more screws that hold the floor to the c-channel in areas where it is not supported by the frame. There are also bolts going through the c-channel then the floor then the ends of the outriggers. The outriggers are basically crossmembers that are attached to the frame at one end and the other end supports the floor. What happens with old trailers is that there is usually a leak at the rear of the trailer caused by a plate that goes under the shell and this funnels water into the rear of the trailer rotting the floor and frame and eventually the rear end separates when everything is rotten back there. The rear bathroom adds extra weight and accelerates the process.

Perry
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Old 08-20-2014, 12:09 PM   #3
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Typically, the frame is on the bottom, the subfloor (plywood layer) sits on top the frame, and the shell sits on top of the plywood, forming a sort of sandwich. The shell makes contact with the plywood via U channels that are riveted to the shell. There are bolts that go up through the frame (typically through an extension of the frame called an "outrigger"), through the subfloor, and through the U-channel, and there is a nut and washer on the topside holding it all together.

You also have the bellypan (the aluminum that covers the underside of the frame) that wraps up from underneath and is riveted to the shell. This isn't really structurally critical--ie., the shell isn't held to the frame by the bellypan wrapping up from underneath--its held in place by the "elevator bolts" that come up through the outriggers, through the floor, and through the U-channel.

70's trailers have a U-channel that also has a C-shaped section that attaches above and below the subfloor, but the sandwich described above is still essentially the same.

The "rear end sag," or "rear end separation" is common on 70's trailers, but can happen to any of them. This occurs when the plywood subfloor rots away in the rear and allows the shell and frame to move independent of one another (at least to the extent that the bolts will allow). This relative movement often results in the rivets in the rear aluminum panels tearing out, or the bolts breaking/disintegrating, which allows the rear end to move even more freely. Also, if the plywood has rotted that badly, the frame is usually rusting away as well, and often the rear hold down plate, the rear most cross member, and the rear frame rails can be so badly rusted that they have to be replaced.
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Old 08-20-2014, 01:19 PM   #4
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Hi Lisa,
As stated in the above posts, the steel trailer frame supports the plywood sub-floor and the plywood supports the shell. The plywood is connected to the frame and cross members with flat-head self tapping lag screws creating a solid platform. Then the c-channel that is riveted to the shell, sits on top of the plywood and is bolted through the ply all the way around the trailer. This gives the strength and flexibility to these beauties.
Also stated that in the rear of our older models the shell/skin stops at the point of the rear cargo lid and will allow water to seep into the plywood sub-floor (bad design). Causing the plywood to rot and bolts to rust, thus allowing the dreaded (rear end sag/separation) to happen.
It really doesn't have anything to do with the rear bath. It happens to all of these trailers.
I have solved this on my 64 restoration. I fabricated some 2" aluminum flashings that I placed between the edge of the plywood and the skin. Not an easy fix, requiring a metal break and a metal stretcher for the curves.
Here are a couple of photos.


Dennis
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Old 08-21-2014, 09:09 AM   #5
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thank you. so behind the coil of white wire do i see metal that stops, then a little plywood, then blackness? and did you replace the whole back panel there with the lights in it or add the flat thing? what's sticking up from the flat thing? rivets? and do you have a before pic of the back end separation from the outside?
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Old 08-21-2014, 10:13 AM   #6
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Rear end separation, unless it is extreme, is often hard to see at a glance. You probably won't actually see the bumper and frame drooping at the rear of the trailer unless it has become completely free of the shell, and the frame rails are so rotten that it sags under its own weight. One of the best ways to check for the presence of rear end separation is to step up on the rear bumper. You should not see relative movement between the shell and the frame rails as you put weight onto the bumper.

As mentioned above, the rear end separation isn't caused by having a rear bath, but it can be aggravated by it. The repair described above is essentially creating an "L" shaped flashing where the vertical part of the L is behind the rear panel, and the foot of the L extends out horizontally on top of the bumper trunk. This fix is best implemented during a complete rebuild of the rear of the trailer, typically to correct a rotten floor. It isn't something most trailer owners would do as a simple preventative measure.
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Old 08-22-2014, 01:04 PM   #7
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Hi Lisa,
Sorry about the confusing photo. Yes the metal on the floor behind the coil of speaker wire is the c-channel I was trying to show you. The blackness is some of the factory original coating Airstream used as sealant or glue for the insulation (not exactly sure) it was everywhere on the inside of the skin.
Yes I did replace the rear panel and added back up lights. There used to be an access hatch there.
The things you see sticking up from the flat thing (bumper mounted cargo space, lid) are called Cleco fasteners. They are used to hold things in alignment to drill or rivet.
Sorry no before photo of the rear end separation. As "Belegedhel" stated it is often hard to see it. The best way to it would be to stand on the bumper and bounce up and down.
Here is a better shot of the c-channel, maybe.

-Dennis
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Old 08-22-2014, 09:44 PM   #8
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i love this forum. thank you all so much.
Lisa
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Old 08-23-2014, 05:07 AM   #9
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i guess one last question. Why is the floor sandwiched between the shell and the frame?
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Old 08-23-2014, 07:32 AM   #10
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Airstream in their less than infinite wisdom decided to tie the aluminum superstructure to the steel frame through the wood floor. It somewhat solves the problem of bimetallic corrosion and ties the whole thing together in a ridgid box. But wood is the material that goes south first. If they had used something that wouldn't rot then there would be no separation issues but the cost would be great.

My trailer is forty years old and it was largely intact, so they must have done something right.
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Old 08-23-2014, 05:08 PM   #11
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:-)
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Old 08-23-2014, 06:25 PM   #12
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I have a picture that is a cross section of how the frame is connected to the shell. let me dig around and find it It was the only thing that made sense to me finally.
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Old 08-23-2014, 06:39 PM   #13
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Shell cut-away picture

This kept me from forgetting how the whole thing goes together.
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Old 09-20-2014, 10:25 AM   #14
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This is a great forum.

My '76 Safari (about to be separated from it's frame this weekend) also has a special extruded aluminum shape instead of the simple channel above but only in the midship section probably because it would be difficult to form this shape into a radius as there is an additional channel that wraps around the edge of the wood floor. I'm thinking about sawing this portion off so I don't have to fit the new floor into the channel during reassembly which would probably require a split lengthwise to get it in the channels.

I'm guessing the design thought was either better sealing at the edge of the wood or additional edge strength? Or maybe it made factory assembly easier by attaching the holding the floor section to the top before it was all dropped on the frame?

Thanks for the pic.

Tim
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