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Old 06-20-2008, 01:37 PM   #1 (permalink)
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Building an offroad 5th wheel trailer

Like usual I am a day late and a dollar short.

Did not even know Pirate had added this forum.

My bad

anyway.... looking for advice.

my thoughts and purchases have been aimed at making an offroad Expedition Camping Trailer to go with my unimog 404 dieselized. Why? That way I can disconnect and do trails like the Con.

So I've purchased a 1985 Egg Shell Scamp fiberglass 5thwheel. Obviously it will need lot of reinforcing since the shell is just screwd/fiberglassed onto its wood deck. This is bolted to a frame wiht trailer axle. More on frame and axle below.

Open to suggestions in the catagory of reinforcing the trailer body to deck attashements. One of my thoughts is to add some wood or metal framing into the insides and glass it to the camper body and screw/bolt glass this to the deck?? Maybe an Exo Skeleton outside could be tied to it?

For axle etc. was thinking plop it ontop of a cut down military trailer that I already have. An M103A3. Not sure if I should keep the 5thwheel trailer's own frame installed (beefed up) and put some type of suspension on this attached the military trailer's frame, like say how a Mog fire box is attached to the mogs frame. This would be; if it would work, to take more shake and bob out of the trailer so it does not fall apart from ruff road travels. Maybe utilize big rig cab suspension parts in this. They are suprisingly not very expensive.

I could go with a fith wheel attachement in the bed of mog like normal. Not sure how effective simpler fith wheel hitches work off road though.

This M103a3 trailer would like it is, give me option to tow it with existing Military Pintel hitch, with bed area of camper above the tounge. Maybe mount camper to military trailer to where the camper's body still sits same way it would as if it had the fith wheel hitch stll attached? The camper bed over top of mog flat bed but pull with pintol hitch still. I would think the over head bed area of the camper would get whacked by the Mog's bed pulling it like this though. Like when nose of Mog goes down lifting its tail upward yet camper still sitting horizontal.

Or turn the 5th wheel camper around and mount it on the military frame backward. Tow it pintol hitch and use the under the bed area; that is now in the rear, as storage for motorycyes spare tires etc.

what is yall's thoughts.

PS- I can't find the picture attaching method. Is Pirate back to you have to have a paid for red star to post pictures? Or am I just missing something.
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Old 06-21-2008, 12:12 AM   #2 (permalink)
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Use the same rotating pintle setup the military has used for years. I think trying to use a 5th wheel on rough terrain is asking for trouble.
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Old 06-21-2008, 12:55 AM   #3 (permalink)
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Im thinking the pintol is better too. wonder if you could mount a pintle in the Mog bed in a simular location as a fifth wheel would be mounted??

BTW this camper is lighter than most and the hitch is actually a ball hitch that goes in your bed and not a plate type fifthwheel.

hitch weight around 450-500lb
Total weight 2200-2500

radiobox Im removing from Mog is around 2000lb itself.
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Old 06-21-2008, 01:25 AM   #4 (permalink)
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A gooseneck will definitely not give you enough articulation to keep it from damaging the hitch on one or both vehicles. Chances are, the trailer you already have will not take any more punishment and rough terrain than the gooseneck hitch. I would suggest a trailer more like the M103 that attaches to a pintle at the end of the frame. Anything that overlaps the tow rig is going to be at serious risk of stress problems or collision with the tow rig at articulation. With a military pintle hitch and trailer your main worries are getting in too deep of a "V" and having the top of the front of the trailer collide with the top of the back of the tow rig. With a gooseneck or 5th wheel design, the trailer can tilt and hit on the sides of the overlapping part or on either end when the rig is in a "V" or going over a peak.

It all depends on what your idea of trails are and what type of trip you are planning. If you are never going to leave the dirt roads, then a 5th wheel or gooseneck could be fine. If you are going to pull the trailer into rougher terrain, then it's simply not going to cut it. The hitch design is not suitable for this type of terrain and neither would the suspension. Most campers do not have anywhere near the ground clearance to tackle any type of rough terrain in any case. The M103 is a 1 1/2 ton trailer and a good platform to build off of, but if your vehicle cannot actuate the air over hydraulic brakes, it wouldn't be safe in stock form.
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Old 06-21-2008, 01:27 AM   #5 (permalink)
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Do a little looking before you go reinforcing the trailer. The construction is pretty sturdy, but you should do your best to make it a smooth riding suspension to prevent jarring it to death. I've taken gooseneck style hitches a lot of places you can't get a bumper pull trailer, but they do have their disadvantages. Maybe since it has such a light tongue weight you could mount it to the back of the mog like a traditional bumper pull, but with a military pintle hitch mount. That way you would have the best of both worlds.
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Old 06-21-2008, 07:45 AM   #6 (permalink)
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Quote:
Originally Posted by Elwenil View Post
.... If you are never going to leave the dirt roads, then a 5th wheel or gooseneck could be fine.
. If I had my way I would pull it over the Con but so far have not found a way to do that so for a trail that ruff it will stay behind and it will be just me and the mog and a truck bed tent or similar.
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With a military pintle hitch and trailer your main worries are getting in too deep of a "V" and having the top of the front of the trailer collide with the top of the back of the tow rig.
Would assume this to be an issue with any rear pull tow sitation unless your tounge is magical.
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With a gooseneck or 5th wheel design, the trailer can tilt and hit on the sides of the overlapping part or on either end when the rig is in a "V" or going over a peak.
I pictured the V issue already as described in my other post. Didn't think about the sides though so thanks for that.

Wonder if you can clearance enough by going no bed at all above any area that overlaps the back of the truck. So that keeps it frame width which is suprising small on a mog
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.... Most campers do not have anywhere near the ground clearance to tackle any type of rough terrain
Exactly. Hence the mating with the M103
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The M103 is a 1 1/2 ton trailer ..., but if your vehicle cannot actuate the air over hydraulic brakes, it wouldn't be safe in stock form.
This stumps me. Especially since I have pulled that same M103 from OH to FL with the Mog and in braking and driving (except up hill power) the Mog did not care if the trailer was back there or not. Pulled same trailer behind a large IH Flat bed truck from FL to TX and it was a happy there too. Both times it and the tow rig was loaded to the brim.

Most reports of civilian folk I've read about using these trailers do NOT hook up the glad hands.

Still though I have been racking anyones brains I could for years trying to figure out why the brakes on the trailer do not like my mog. Touch any brake on the rig and they lock up solid and will not unlock till I release a glad hand. Any input on that would be appreciated.
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Old 06-21-2008, 07:50 AM   #7 (permalink)
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... Maybe since it has such a light tongue weight you could mount it to the back of the mog like a traditional bumper pull, but with a military pintle hitch mount. That way you would have the best of both worlds.
The advantage of a goose neck or 5th wheel is primarily space compacting (longer trailer yet shorter overalll towing length), turning radious and manuvering due to pivot point above the rear axle. If I'm not mistaken, Once you move the pivot point from above the axle to the bumper area; all advantages of a fithwheel/goose neck are gone.

There is some rare pivoting rear hitches that are suppose to mimic the advantages of a fithwheel. Look at Pullright
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Old 06-21-2008, 12:12 PM   #8 (permalink)
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It sounds like either the Mog is not compatible with the US military's brake system or there is a problem with the trailer master cylinder. You should be able to download the TM from LOGSA or possible off SteelSoliders. Be aware the A3 model has dual line brakes as opposed to the older single line system and has an automatic emergency brake, which appears to be what you are activating.
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Old 07-22-2008, 07:53 AM   #9 (permalink)
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Personally if I was going to do it, the M103a3 trailer is the perfect base for a camper. What I would do is construct a brand new frame on it out of .125 wall 2x2 box tubing with a 100% weld out, then I would put .0625 wall 2x2 box tube in between for uprights to keep it light. I would then sheet the entire thing in sixteen gauge sheet aluminum glued in place with the glue they use for the Boeing 747-400 construction, the stuff actually makes a bond stronger than the aluminum is, it will also be completely water tight, and will have to take a really big whack from something to get punctured.

Then you can gut the good stuff out of your 5th wheel like the toilet, stove water system ect, and in this case you could install one of the new tankless water heaters that ran on propane, install a huge propane cylinder that had a roll cage around it, and a Diesel Generator.

Also could use a watertight style door for a boat, this would ensure that it wasn't going to leak on you. The same goes for the windows, use marine hatches. You would have one tough little camper at that point that would easily go all kinds of places.

Man, I am getting ideas now... but as for retrofitting the 5th wheel, it isn't worth wasting money on. If you need any more advice on this I am a welder/machinist by trade, feel free to hit me up. - Beast
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Old 07-22-2008, 11:27 PM   #10 (permalink)
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Quote:
Originally Posted by coachgeo View Post
The advantage of a goose neck or 5th wheel is primarily space compacting (longer trailer yet shorter overalll towing length), turning radious and manuvering due to pivot point above the rear axle. If I'm not mistaken, Once you move the pivot point from above the axle to the bumper area; all advantages of a fithwheel/goose neck are gone.

There is some rare pivoting rear hitches that are suppose to mimic the advantages of a fithwheel. Look at Pullright
How about 2 mounting points. If your tongue weight would allow it, you could run a normal gooseneck ball in the bed, then when you get to technical areas you could run a hitch at the back of the truck using a different type of hitch. Would take some thought, but I can draw my idea a lot better than I can explain it.
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Old 07-23-2008, 06:26 AM   #11 (permalink)
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How about 2 mounting points. ....
Makes since to me. Might be do able.
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Old 07-23-2008, 09:43 AM   #12 (permalink)
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Makes since to me. Might be do able.
It is a novel concept however unrealistic, the problem you will run into is weight distribution. I used to be an OTR trucker, and have towed a ton of trailers, bumper pull, 5th wheel and goose neck.

The reason for each design is weight distribution. A 5th wheel is going to set more weight over the vehicles rear axle, and use it as its pivot point, as well transfer more of that load to the front axle, thus making the vehicle more stable.

Where as with a bumper pull there is a reason there is a 10% rule, it is because if you start exceeding that number you are going to wind up light on your front wheels, and you will run into steering problems.

There for a trailer that tows great as a 5th wheel, will really suck as a bumper pull because the lever created in the difference of the hitching locations on the tow vehicle.
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Old 07-23-2008, 10:22 AM   #13 (permalink)
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It is a novel concept however unrealistic, the problem you will run into is weight distribution.........
Thanks for the educated responce.

Now the question is does your points of weight distribution match with this atypical combination. Dont think the Unimog will care about weight distribution with such a light trailer body. (around a ton) Its towing copacity is 4 tons. Appears to be far below copacity of the military trailer's axles Im looking at grafting this one to as well.
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Old 07-23-2008, 12:40 PM   #14 (permalink)
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Thanks for the educated responce.

Now the question is does your points of weight distribution match with this atypical combination. Dont think the Unimog will care about weight distribution with such a light trailer body. (around a ton) Its towing copacity is 4 tons. Appears to be far below copacity of the military trailer's axles Im looking at grafting this one to as well.
They are actually very relevant in your situation with this application. I have a 1 ton dually tow rig, the truck weighs in at about 11,500 lbs with my Lincoln Welder sitting on the back of it, a trailer that weighs one ton that isnt properly balanced will keep me from being able to drive more than 45 mph because it will fish tail so hard, and this is with a 2wd dually.

When you start looking at a rig like a Unimog that is equipped with portal axles, and tall tires, that has a very high roll center as opposed to a rig like my 2wd dually.

Where this is going to effect you is when your towing with a vehicle that has a high roll center like that, and you have a trailer that isnt properly balanced it is going to throw you all over the road, and you get off road, and this is going to further complicate the problem.

For your application I would go strictly bumper pull single axle for a reason. if you are configured as a 5th wheel, a 5th wheel works great for when towing down the open road, going forwards. That is why a Semi uses this configuration. However, when it comes to backing up, a 5th wheel needs about the space a B-52 on short final needs to turn in, they just don't handle tight.

Where as a bumper pull actually will come around way faster when backing than a 5th wheel will because the length of the frame from the pivot point of the back wheels, it will actually give you a lever that will allow you to have a greater rate of turn when backing. This is along the same principal why a semi has a sliding 5th wheel, you can distribute the weight, and you can then change where the turning center of your trailer is to make it follow how you need to to get through tight handling situations.

The reason this is so relevant is you are going to be taking this thing places people normally don't take trailers, you are going to be in tight spaces with it, and you need it to handle as tight as possible, especially if you tow it up a trail and have to back up to get another approach at something.

Something else to consider is if you go with a smaller trailer that is custom made to work with your Unimog, it will compliment the places the mog can go and it will all work in harmony. If it is something that is cobbled together, well then it is not going to be so fun. I really think your best bet would be to get a military style trailer as mentioned before, frame it out and add your own goodies to it.
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Old 07-23-2008, 04:11 PM   #15 (permalink)
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Good info much appreciate.

So far from those who seem most in the "know" out of all that have responded; these folk seem to lean toward the OEM pintel set up. So guess thats how I go. I'll first try the 5ver body on the military trailer, and pull it by OEM pintel. If it trashhes the 5ver I can pull it off and build a box on the trailer instead like your suggesting.
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Old 07-23-2008, 06:04 PM   #16 (permalink)
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Good info much appreciate.

So far from those who seem most in the "know" out of all that have responded; these folk seem to lean toward the OEM pintel set up. So guess thats how I go. I'll first try the 5ver body on the military trailer, and pull it by OEM pintel. If it trashhes the 5ver I can pull it off and build a box on the trailer instead like your suggesting.
That is going to be your best bet, you want to get a weight on the trailer and a tounge weight. figure out your distribution from there.
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Old 07-23-2008, 06:28 PM   #17 (permalink)
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Good tech here!


I have a military generator trailer (M-103?) that I use with my truck camper (4Wheel Pop Up Camper).


Camper weight balance/distribution is real important to a smooth haul.
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Old 07-23-2008, 06:31 PM   #18 (permalink)
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Good tech here!


I have a military generator trailer (M-103?) that I use with my truck camper (4Wheel Pop Up Camper).


Camper weight balance/distribution is real important to a smooth haul.
To totally hijack this thread here, but I suspect from your "No Bama" sticker that you have studied your Wilkow properly?
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Old 07-23-2008, 07:46 PM   #19 (permalink)
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That is going to be your best bet, you want to get a weight on the trailer and a tounge weight. figure out your distribution from there.
With those two figures how do I use them to figure best weight distribution? Course this is a whole nother topic. Might be best to start another thread??? "determining best weight distribution of a trailer used offroad:???
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Old 07-23-2008, 08:32 PM   #20 (permalink)
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With those two figures how do I use them to figure best weight distribution? Course this is a whole nother topic. Might be best to start another thread??? "determining best weight distribution of a trailer used offroad:???
Actually the tounge weight is going to simply be the weight at the hitch. and then the weight of the whole trailer, the weight at the hitch should be about 10% of the trailer total weight.

All you have to do is find out where you are at, and adjust your load on the trailer accordingly.
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Old 07-25-2008, 12:18 AM   #21 (permalink)
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You can either shift your weight, or make a sliding axle for the trailer.
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