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Old 01-18-2012, 05:43 PM   #1
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Default Stretching frame on a single

Hi I'm in the planning phase of what I hope will be my last motorhome. I have looked through most of the builds but have trouble finding detail on how you guys stretched the frame. What metal? Is it boxed? I am looking to build a single axle truck that has a 20' box on it as the living space. I plan to tow a 30' stacker trailer that should be about 15k loaded. Also I live in ca and have looked over the rules for converting to rv and it doesn't seem to bad. So what do you guys think? Fwiw I built my tube chasis race car and understand frames being square and axle placement. Thanks for any help to guys can offer
Jason
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Old 01-18-2012, 09:17 PM   #2
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Sounds like it should be pretty doable. I've seen some guys over on the Escapees HDT forum that have similar setups. I think they use C channel to extend the frame back to where they put their 5th wheel hitch. If you're doing a bumper pull trailer you might not even have to extend the frame, depending how long the frame is on your truck. My truck is a single drive axle with a 26' box and it's got a 295" wheelbase. But, the box extends pretty far behind the rear axle. There is a section in that HDT forum that has a lot of info regarding truck frames and hitches and stuff. Most of them just use the truck to pull their 5th wheels and build big decks for cars or cycles or such. But I think some of that info might be of help here. Keep us posted and put up lots of pictures of your build. That seems to be one of the things lacking around here. Lots of projects get started with pics and then we don't hear much. I think they get their trucks done and take off down the road with huge smiles on their faces.
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'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio
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Old 01-18-2012, 10:54 PM   #3
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If I was stretching the frame between or after the rear axle, I would find a donor truck (junkyard) and use the frame sections from it. Dragonslayer has an ongoing post about his build that you can check out. Renegade, Haulmark and other builders want double frame rails but Showhauler and NRC can use a single by the way they manufacture the floor and wall section, which help reinforce the frame. Good luck on your project.
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Old 01-19-2012, 10:08 AM   #4
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Do you guys have any pics of how the other companys are doing it? It seems from what I have found class 8 trucks arent available with a long wheelbase. By that I mean I want to have a 20' box after the cab. I was thinking of using the same size C channel to extend the frame then getting a samller size C channel that will fit in the existing C channel and basically box it in like



I have seen where people just add a new section of frame and seems like they just weld a fish plate <> where the frame is added but that seems like it wouldnt last.

Also I have seen plenty of class 7 trucks that are exactly what I want in a chassis just the engine is a smaller cat or cummins at only 250/300 HP. I think that will hurt the milage and the point of doing this. I want a big truck for safety/power and reliabilty.
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Old 01-19-2012, 10:11 AM   #5
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Bob I saw that you tow a race trailer around how does the truck handle it with that much overhang? I am going with a bumper pull trailer. Do you ever wish you had twin drive axles? Also do you know your gross weight?
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Old 01-19-2012, 01:11 PM   #6
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I Think the thread Gordy was referring to is "Frame stretching" by Kenn, Unfortunately my build is still on the drawing board, and is at least a year away from becoming real... although since I work in the engineering field I will probably redesign it six more times before I actually start. Kenn is doing a great job of documenting his build though and a lot of good ideas can be gained from him.

Dave
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Old 01-19-2012, 02:17 PM   #7
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I just read his build thread and found that he has a 243" wheelbase tractor. That would work for me. I have no problem or concerns stretching the frame after the axles I was worried about doing t before the axles. Kenn's thread is everything I want to do and the older Pete's are reasonable to find. Are most of the tractors with sleepers and twin screws that big of a wheel base? If so that would be perfect. I read that after they remove the front axle then they end up with 270" or so. My project is still in the planning stage also. I am looking through all the forums I can find to figure out how the frame is built and what wall tubing. Seems 2x2 is common I have seen 3/16" being used for the wall. What about roofs? I see people saying aluminum is the best but where do you get 1 piece that is that big ? Can you buy the bullnose corners from a trailer place?

Sorry for all the questions this is just something I found out that I can build and afford.
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Old 01-19-2012, 03:24 PM   #8
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Tractors come in quite a few wheel bases, over the road units usually will have the longer frames due to big sleepers, In my opinion its always best if you do not have to cut and stretch a frame, and adding frame rails after the drivers is pretty easy and not to much money to have a frame shop handle it if you do not want to do it yourself. 2x2x3/16 tubing is going to be pretty heavy (runs 4.3 lbs per foot) and expensive. I am planning on using 1-1/2" for the walls with some heavier tube at the corners and around the roof for added shear strength. Seems like the most popular roof materials are aluminum, rubber (EPDM), and fiberglass. Each has definite good and bad traits. Personally I tend to lean toward 60mil EPDM rubber, installed properly is a good 20+ year roof. The company I work for builds mobile office trailers, and we have hundreds of units out there and the rubber has hold up the best, and is easy to patch. It is easy to install and seal. Aluminum is also a good choice and is available in sheets or in a full length roll.
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Old 01-19-2012, 03:57 PM   #9
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Being an engineer what wall 1 1/2" would you run? I agree that would be heavy. And for the corners would you run 2" or just thicker 11/2"? Would you mind sharing you plan such as material specs for the floor And the walls and roof? Thanks
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Old 01-20-2012, 10:52 PM   #10
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Currently I am leaning toward 11ga for studs and general framing, I have not made a decision on the corner posts yet, but am thinking of building a L shaped composite post from 3 studs, that way the corner is not thicker than the rest of the wall. I plan to frame my interior walls with steel tubing also so they become an integral part of the overall box assembly. The biggest concern for me on the construction is to eliminate as much moisture as possible from the vehicle. Steel studs will transmit the cold through the wall and create condensation, i will be adding a thin layer of rigid insulation board over the entire wall before i sheet the inside. I plan on using 7/16 osb or 1/2" exterior grade sheathing over that. The exterior rated glue in these products creates a moisture barrier if all the panel seams and penetrations are sealed. Same construction for roof and floor, except thicker T&G ply for the floor. All walls and ceiling cavities will be filled with expanding foam insulation after all electrical conduits and piping is installed. Underside of the floor will be 26ga galvanized sheet metal, and I am trying to decide if it will be undercoated or perhaps spray on bedliner material. outer siding i am not sure on yet, but probably .060 aluminum with VHB tape to insulate it against the steel studs and prevent electrolysis. Heating will be provided by a diesel fired boiler with radiant floor heat, and a basement heat pump for cooling. moisture buildup will be greatly reduced by using a air to air heat exchanger. I want to keep as much off the top of the truck as possible as I am already going to be plenty tall. I still have some serious design challenges to squeeze what I want into the rig, but as what I want is not mainstream I will not find a rig from one of the standard builders that meets my needs.

Dave
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