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 > Anyone knowledgeable about fifth wheel construction?

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howardwheeler

West, Texas

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Posted: 10/11/18 11:37pm Link  |  Quote  |  Print  |  Notify Moderator

A couple of weeks ago I had a major frame failure on my fifth wheel. I posted about it with some pictures a week and a half ago. The main metal beam that goes to the nose cracked. We got that welded up to where it won’t crack again. But when we had torn the inside out to uncover the whole frame around the pin box and the beam that extends back to the main chassis frame, we could not find any way that the side walls of the trailer—the “box” you live in—connected to the frame in the front that supports the pin box and the whole front that extends over the pickup bed. We could find nothing obvious that was broken that would have connected the wall, floor and roof structure to the heavy rigid metal frame that extends to the front. So we surmised after having fixed the frame that the front must slightly float or flex around the metal frame. I have decided that is wrong. My pin box is now rigidly welded up, but the front wall structure can move up and down as I travel independently of the pin box approximately 1 inch. It does effect the inside closet. So I’ve now decided that what might have broken first, before the main frame broke, was whatever attaches the wall structure of the camper to the frame up front. The loss of that additional rigidity that the wall structure would have provided then allowed too much stress on the metal frame. That’s my thinking. So my question: does anyone know for sure that the front section of a fifth wheel is in fact hard connected to its rigid supporting frame, and, if so, how do they connect? I can see how that main body is connected with bolts going up through the outriggers off the main beam and then connecting to the wall structure, but we could find nothing up front. I imagine it varies from fifth wheel to fifth wheel but are there generally accepted ways the front wall structure is connected to the main supporting frame? Anyone know how a fifth wheel is put together up front? Or does anyone know somebody who used to work at Alpenlite that’s still around that would know how they were put together? I’m puzzled.

JIMNLIN

Oklahoma

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Posted: 10/12/18 07:05am Link  |  Quote  |  Print  |  Notify Moderator

The trailers exterior walls are connected to the outriggers on the ones I've delt with.


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elkfarmer

texas

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Posted: 10/12/18 07:50am Link  |  Quote  |  Print  |  Notify Moderator

They used a Sturdi wood floor that extended over the outriggers. The vacume bonded walls sat on the outside of this floor and was bolted through. The walls were connected with the vacume bonded roof. If the frame has been fixed the only logical conclusion is that one or more of the bolts holding the wall down have probably wallowed out and broken the base of the wall tubing that adjoins the two. They used a very thick aircraft grade aluminum that if this is the case you could probably send some lag bolts up from the bottom with adhesive and hopefully tie it down. The one I had for 16 years was not fixed to the frame as you are asking.


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howardwheeler

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Posted: 10/12/18 07:54am Link  |  Quote  |  Print  |  Notify Moderator

The main lower floor is indeed connected that way, but the nose section that is the bedroom is not. The frame of that section expands out to be almost the width of the trailer but stops just inside the walls. There are no outriggers. In other words, the pin box frame and the two rails on either side that connect it to the main frame are basically the inside wall to wall width. But we could find nothing obvious that connect up there that portion of the frame and the wall structure.

howardwheeler

West, Texas

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Posted: 10/12/18 08:04am Link  |  Quote  |  Print  |  Notify Moderator

Sorry Elkfarmer, I posted my reply before yours showed up. The frame over the nose is above floor level unlike the main lower section. So any bolting would have to be through the side wall or up from the floor into the beam. But we found evidence of neither

elkfarmer

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Posted: 10/12/18 08:08am Link  |  Quote  |  Print  |  Notify Moderator

The nose section sits on the sturdy floor. The wall structure is one piece lifted into place. I would assume the nose section is bolted down to the floor since(in mine) the frame ran inside the wall(in the coach) and was covered in carpet. The flooring extended out beyond the frame to allow the nose section to rest. You will probably have to drop the fiberglass around the pin to access these bolts. That's were I would start. Hope this helps.

Retired JSO

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Posted: 10/12/18 08:16am Link  |  Quote  |  Print  |  Notify Moderator

Not sure about the remainder of the side walls but the front overhang is screwed to the frame from the bottom up. Been there to weld a broken beam and saw where they had missed every other hole.





troubledwaters

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Posted: 10/12/18 08:25am Link  |  Quote  |  Print  |  Notify Moderator

Can you lag bolt it or carriage bolt it from the top down?

howardwheeler

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Posted: 10/12/18 08:40am Link  |  Quote  |  Print  |  Notify Moderator

Yes. The frame was inside the closet floor where the pin box section was and the frame rails were above the floor, the passenger side covered by carpet inside the lower bedroom cabinets and the drivers side mostly under the bed slide out. So how was yours connected? We found no evidence of any bolts and the outside fiberglass is completely intact. Maybe it has some places where the trim is ever so slightly moving.

elkfarmer

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Posted: 10/12/18 09:09am Link  |  Quote  |  Print  |  Notify Moderator

I am just going by what I saw at the factory in 1998. I just watched as they picked a wall unit up and proceeded to adjoin the two. I did a lot of work on it but I never had a broken frame so didn't have to do what you are doing. From what I saw it was exactly as I wrote earlier. There very well could be some ears/flanges like JSO said on the underside. My model sat on the floor and was screwed up from the bottom into the aluminum wall structure. It was not fixed to the frame. If it is moving that much I think the screws in the top have pulled out and probably a bolt or two on the main deck has pulled loose as this is a vacuume bonded wall and very rigid. You will have to take the fiberglass off from the pin area to the bay opening and access the screws from underneath

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