Camper Build

iandraz

Adventurer
Starting a thread for my new FG camper build....the base truck is a 2004 Fuso FG purchased at an auction. Its previous owner was Sunbelt Rentals, think it was a general service truck. Here's a picture just before lifting the service body off:



I just finished making the first set of mounting brackets for bolting the 4 point pivot frame to the truck frame:





This is going to be the Unimog style pivot frame with a bushing at the front and back, and rigid mounting in the middle.
 

kerry

Expedition Leader
Great. I'm looking forward to this thread. With the service body off, it must be very easy to inspect the frame. Have you seen any evidence of any frame problems on the truck? Any idea on the weight of the service body? How did you get it off? Have you given any thought to strengthening the frame given Doug Hackney's experiences?
 

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iandraz

Adventurer
The frame seems solid. There are a couple of rust spots where the service body rubbed against the frame, and where the frame was modified in the rear to fit the trailer hitch. But other than that it seems good. Fortunately the truck is new enough that the problem areas didn't evolve into anything major.

Getting the service body off was a chore...the mounting to the frame didn't appear to be too well thought out...weird shapes of metal at not-quite-straight angles, and it was even tack welded to the frame in a couple small locations. Fortunately, once found these were easy enough to remove with a dremel and grinding disk. Also the mounting on the rear went over and under the frame in a way that required cutting the service body mounts off with a sawzall to get the clearance required to pull it off. Apparently the mounts were welded on after fitting the service body to the frame? Getting it all off was not a fun job! After all that it was a fairly simple matter of lifting the service body with blocks and 2 hi-lift jacks, then driving the truck out from underneath.

Regarding frame reinforcements - I'm not planning on making any changes to the frame (or basic truck for that matter). Mitsubishi's put a lot of time and money into getting this design right so I don't want to touch that if I can. On the Hackney truck, I think the 3 point mounting, frame extensions, and weight may have amplified the stresses in the frame significantly. With this 4 point mounting to distribute the forces, standard frame, and lighter weight, I think I should be good as-is.

- Jacob
 

lehel1

Adventurer
awsome ; )

hello
looking forward to seeing how your project comes along.

we just picked up our new 08 fg from pioneer services in sacramento and are in the planning stages for our camper.

it you need, i currently own a unimog expedition camper, and would be glad to send you detailed pic's of the 4 point mounting system used on it and the camper bottom.

i'll be writing some on on pickup experience soon, and want to thank those that offered to post pic's here for me (since i havn't quite figured taht out yet). i will contact you guys soon for that help, thank you again

seems like we have a great forum here

cheers lehel and laura
 

Tree

Adventurer
Sweet! :victory:If you need help with the pics Im here for you buddy.

BTW what kind of unimog do you own?
 

dhackney

Expedition Leader
Congrats on the build!

Great to see another FG coming together.

On the Hackney truck, I think the 3 point mounting, frame extensions, and weight may have amplified the stresses in the frame significantly. With this 4 point mounting to distribute the forces, standard frame, and lighter weight, I think I should be good as-is.
I agree with your assessment. Those considering a 3 point design need to make certain that the amount of weight they are proposing to load onto two widely separated points on the FG frame are within its design limits.

I encourage people to consult the Fuso body builder's manuals available here: http://www.hackneys.com/mitsu/index-chassis-photos.htm

For those interested in reinforcing the frame rails or the step down section, there are detailed instructions in the body builder's manuals. It's a lot easier to do before you build than after... :)

Also, Darrin at RUF has found Fuso North America very helpful with reviews of his sub-frame designs. The Fuso guys have the engineering horsepower to know if what you are proposing is within the design limits of the frame. Believe me, it's better to find out now that what you think will work will actually work. The alternative can be pretty ugly...



Believe me, you do not want to discover that in come remote corner of the planet.

The extremely important issue with the Fuso frame is that like nearly every truck in its class, the frame tapers down to a small cross section aft of the rear axle. Check the section modulus diagram of the stock frame to get an idea of how much weaker that section of the frame is than the area in front of the rear axle - 45.9 cm(3) / 2.8 in(3) vs. 72.3 cm(3) / 4.41(3) - nearly half as strong.

The issue with 3 and 4 point pivot frames is the load point aft of the rear axle. I have no way of knowing what load we were putting on our mounting point back there, but whatever it was, it was too much. Michel reports his FG frame also bent back there with a 3 point pivot design.

You may have no problem for a long time; we didn't for more than a year, and during that time we were on some very challenging roads and tracks at a higher weight than when it bent, cracked and broke. But all it takes is one winching, one unseen-in-time speed bump, one big rock in the dark, or one whatever and you could have a problem.

A four point design will help distribute the weight of your payload over three places on the frame instead of two. IMO, it is a good choice. If you are not going to reinforce it back there, be careful how much payload weight your design can possibly pivot towards the rear.

I plan to convert our payload to a system that distributes the load over the length of the entire frame.

Congrats again! Looking forward to seeing your project progress.

Please let me know if I can be of any assistance in any way.

Doug
 
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lehel1

Adventurer
4 point mount

hi again

our unimog camper has a torque tube that runs thru all three camper side mounting plates on our 4 point mounting system. i'll see if i can explain this alittle,

the front and rear mounts are on a center bolt, so if you can imagine you have a top cross plate 3 feet long or so mounted to the camper bottom, the other half monuted to the truck frame. i beleive there been many pic's of this shown on this site. now the center mount is a fixed mount across to both truck frame members. o.k. so three mounts are there, now there is a tube welded from the rear camperside bracket to the center camperside bracket, then another tube continuing from the center bracket to the front camperside bracket. well, i'll get one of you to post pic's of this.

anyhow, one thing i noticed is most custom 3 or 4 point mounting systems i've seen so far seem to be at the extreme ends of the truck frame. our unimog frame which is the stock setup from unimog has the rear and front mounts in alittle over two feet in from each end.

our current plan is to use our 14' flatbed as the top frame supporting the camper fully flat from front to rear, and mount a 4 point system closer in from each end on the truck frame. this perhaps will bring the front mount almost 2.5 feet or alittle more back from the cab right where the reinforcement plates are for the step down frame, the back one will be in from the end almost 4 feet (which includes the 2 additional feet added because of the 14 foot flatbed) putting it very close to the rear spring shackles. with an existing camper frame i beleive there won't be a need for the mounts to be futher toward the extreme ends.
our concern at the moment is any up and down movement of the upper frame vs the twist factor of the truck frame between the three mounts.

pics will tell more and i'll work with one of you soon to get these posted on here

cheers lehel and laura
 

dhackney

Expedition Leader
iandraz,

The body builder's guide will give you detailed information on the clearances required for rear suspension movement, etc.

Be sure to include the tapered hardwood specified in the ends of your mounts, or use a "fishmouth" cutout as Darrin Fink does in his RUF designs as illustrated in this photo from Darrin (I added the arrow):



Here are Darrin's comments related to the non-tapered and non-fishmouth cutout method used on our truck's payload mount subframe:

"The sharp edges of the body or bed mounting cause stress risers which sort of amplify the load stress onto the frame. All Fuso BBMs recommend either tapering some oak boards up and away from the frame on the ends, or cutting stress relievers into the subframe at the ends.

The angled "fishmouth" notches cut into the ends of the subframe massively reduce the stress on the flanges. If I left those square, even the much stronger FM frame might break there.

It IS ENTIRELY POSSIBLE that you could have broken your frame even under weight capacity!"


So, the message is, be sure to taper the load you are placing on the frame on the ends of any subframe mount. If you just cut them off straight or have a flat end on them as we did you could be introducing stresses that the frame will not be able to handle.

Again, try contacting Fuso engineering. The worst they can say is "no," or perhaps worse, "that's a really dumb idea," but it's better to find out now than later. Darrin says he iterated many designs with them prior to his first build on an FG and found them very helpful.


lehel,

The moderators would probably prefer that you start a new topic with your design and project so we don't hijack iandraz's thread.

I will comment on your proposed design since some of these comments may also be applicable to iandraz's project.

Doug


this perhaps will bring the front mount almost 2.5 feet or a little more back from the cab right where the reinforcement plates are for the step down frame, the back one will be in from the end almost 4 feet (which includes the 2 additional feet added because of the 14 foot flatbed) putting it very close to the rear spring shackles.
Please see the comments above regarding "stress risers" in the frame. The two most stressed points on a typical truck frame are right behind the cab and at the spring shackles. You are proposing putting your two load points directly on those spots. This would probably be a very good design to have the Fuso North America engineers review and comment on prior to implementation.


Here is an informative article on truck frames, modifications, etc.

http://trailer-bodybuilders.com/mag/trucks_tips_truck_frames/
 

kerry

Expedition Leader
Thanks for posting that link on truck frames.
At the end of the piece he writes that it is better to rigidly attach a body at the rear and float it at the front. Can anyone explain why this is the case? My service body is bolted thru the web and welded to the frame at the rear and u-bolted at the front so it seems to have been mounted with similar advice in mind.
 

iandraz

Adventurer
Great input on frame stress...I'm coming up with some ideas about how to distribute the load over a larger area than what I have now, with some minor changes.

I do agree with what lehel is saying about moving the front and rear mounting points in a bit so they aren't right at the edge...if you think about it this allows an even distribution of weight so each mounting point carries an equal load.

Just finished the rear mounting (this is mostly taken directly from my original Unimog camper project):



The photo makes the rust look kind of bad, it really isn't very deep! I probably need to brush down the trouble spots and repaint.
 

dhackney

Expedition Leader
Can anyone explain why this is the case?
[total and complete speculation] My only guess (note: guess) is that it is related to the stress point of the frame at the rear of the cab. If the payload is "floating" at the front attachment point, it would lessen additional loads into that stress point. [/total and complete speculation]
 

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dhackney

Expedition Leader
iandraz,

Note the difference between your pivot point mounting (which looks very similar to ours) and Darrin's.

Darrin spreads the load of his mount longitudinally along the frame with the yellow sections that end with the "fishmouth" cutouts. You could do the same by notching or shortening the flange section on your pivot.

Check the frame section modulus here: http://www.hackneys.com/mitsu/docs/fusoframesectionmodulus.pdf

Note that your rear mount is in an area of the frame that is significantly weaker than where your other mounts will be placed.

By having all the weight carried by the two brackets and the U channel of the pivot mount, you are loading the frame only in that short section; it will be a stress riser in an area of the frame that is already, by design, weaker than the forward parts of the frame rails, as well as very close to the spring shackles.

If you don't implement the type of load distribution rails that Darrin used, consider using extended brackets that would spread the load along the frame web. Be sure and angle them at 45 degrees or less, just like the ends of a frame reinforcement (the angle is to minimize or eliminate stress risers - details in the body builders manuals - page 8 here: http://www.hackneys.com/mitsu/docs/fusoframemodificationinfo.pdf).

Doug
 

lehel1

Adventurer
frame

hello all

great info ?? thanks for the note and all the great info doug, i am planning on starting a new thread for our project ; ) i hope i havn't intruded in anyones space here.

i myself have enjoyed talking with darren the last couple of years about expedition campers, it would be great to have him do a detailed writeup on his projects one day ??

one area we are now looking very closely at is the load from the bottom up, or the suspension end. the overall goal for these type of campers seems to be to allow the truck frame to twist naturely. as well we'd certainly like to prevent a camper subframe from twisting and destroying a camper box.

a novel approach if it was possible might be mounting a camper subframe right on to the spring shackle mounts at the front end as well as the rear suspension. the truck would have its own supporting structure, and the camper subframe on its own independant from each other.
a camper 2 or 3 point subframe will put undue stresses on the trucks frame regardless of how or where it will be mounted. our regular style working flatbed on our new fg is mounted sitting on top the whole frame and then u-bolted. the truck frame has reduced twist now but very evenly supported on the frame. although the flatbed can have some twist as well now. anything less than this gives the frame more twist but less mounting surface. hope i'm not babbling to much here.

anyhow, i bring this idea up as something to add to our overall view, as we're all finding it can be quite a feat to try using the trucks frame with the suspension mounting points pushing from the bottom against the mounting points from our camper subframes pushing against the frame in the other direction.
as we extent away from the suspensions mounting points the frame will now have a new twisting action against the nature twist were trying to keep. the frame as a whole will flex up and down agains't the suspension mounting points creating hot spots at different spots along the frame which could very well cause severe cracking. along with this it can be made even worst by a heavy built camper swinging back and forth extenting the frame twist beyond its cabability creating more hot spots.

the unimog design seems to be less affected by the frame stresses as the drive train is all very connected by its own support work. an example is the rear end diff alignment is not connected or controled by the rear suspension but is connected to the sealed driveshaft tube by supporting tubes. the rear suspension itself only controls up and down movement via coils.

its all quite a compromize, whew. well thats my idea's so far
enjoy hearing more on others veiws

cheers lehel
 
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