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Thread: pivoting frames and mounting campers

  1. #1
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    Default pivoting frames and mounting campers

    hey doug

    here you go ; )

    look forward to seeing you at the expo

    cheers lehel and laura

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    Lehel,

    thanks!

    I will attempt to copy as much discussion as I can find related to camper box mounting and pivot frames that is spread all over this forum into this thread. If anybody else has some time and wants to start, please do.

    In the meantime, those desiring to learn a little bit about 3 point pivot frames can start here:
    http://www.hackneys.com/mitsu/index-pivot-frame.htm

    I'll try to add in the info on 4 point frames and other designs as soon as I can.

    Doug
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    Charlie,

    Would you be willing to post pictures of your U500 / Unicat 4 point mount?

    Tom

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    Thread goals:
    • Consolidate all relevent posts about camper box suspension / pivot frame systems into one place.
    • Engender and facilitate discussion about this topic.
    • Provide an authoritative resource for people designing, building and using expedition campers who wish to learn more about this topic.



    Thread realities:
    • The majority of the initial posts in this thread will be copied from other threads. Quotes contained in these initial posts will refer to posts that may not exist in this thread.
    • I do not follow, read or monitor threads or topics other than Mitsubishi Heavy Truck and a little bit on General Expedition Camper Discussion and Modifications. I will not be aware of those threads/topics and am unlikely to include those posts in this thread. There are undoubtedly threads in other areas that contain relevent discussion. I encourage others to copy those posts into this thread.
    • There will be little to no attempt to maintain time or topic continuity when I copy and paste into this thread from other threads/topics.
    • There will duplication and repitition between posts.



    Thread assumptions:
    • The Fuso FG has a very flexible frame. Unlike light duty trucks or standard road medium and heavy trucks, the frame is design to twist, somewhat like a Unimog's frame is designed to twist.
    • The torsional twisting of the Fuso FG frame can introduce forces into any payload that is rigidly mounted to the FG frame.
    • If a designer/builder/owner wishes to isolate their payload from the torsinoal forces of the Fuso FG frame, a payload (camper box) suspension or pivot frame system can be implemented.
    • The purpose of a payload suspension or pivot frame system is to isolate the payload from the chassis frame, not to reinforce or strengthen the chassis frame.



    Thread known facts:
    • Information regarding mounting payloads onto the Fuso F series trucks, including the FG, is included in the Mitsubishi Fuso F series body builder's manuals available here: http://www.hackneys.com/mitsu/index-chassis-photos.htm
    • Information regarding 3 point pivot frames is available here: http://www.hackneys.com/mitsu/index-pivot-frame.htm
    • Mitsubishi Fuso North America engineering has provided engineering review and design support for successful 3 point pivot frame installations on FG and FM series trucks (Darren Fink / RUF http://www.ruf-inc.com/ )
    • If not properly designed, implemented and loaded, a 3 point pivot frame can stress a stock FG frame beyond its design limits. http://www.expeditionportal.com/foru...ad.php?t=24225
    • Unimogs successfully employ 3 and 4 point pivot mounting systems for vehicle components (engine, cab, etc.) and payload.
    • Fuso FG expedition campers have been successfully designed, built and utilized without 3 or 4 point pivot systems. http://www.questconnect.org/
    • Fuso FG expedition campers with 3 point pivot systems have circled the globe. (Carl & Mary Hunter)
    • There are no known fact/science/engineering based publicly available reference sources for analysis of potential payload suspension / 3 or 4 point pivot systems for the Fuso FG.
    Last edited by dhackney; 03-31-2009 at 05:08 PM.
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  5. #5
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    Threads dedicated to or containing significant content related to payload suspension systems / 3 or 4 point pivot frames include, but are not limited to:

    Torsion-Free Sub-Frame http://www.expeditionportal.com/foru...ad.php?t=11709

    Subframe Mounting & Suspension Mods
    http://www.expeditionportal.com/foru...ad.php?t=22229

    3 point pivot frame info
    http://www.expeditionportal.com/foru...ead.php?t=6120

    Broken frame
    http://www.expeditionportal.com/foru...ad.php?t=24225

    Camper Build (iandraz's build thread that was hijaacked by this topic and was the inspiration to try to move such discussion to this thread)
    http://www.expeditionportal.com/foru...ad.php?t=25205


    If you know of or find others, please post them in this thread.
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  6. #6
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    I will start the content portion of the thread by addressing the one known failure of a 3 point pivot system on an FG, which was on our truck. (Please note that Michel has also reported bending in his frame, but I don't know the extent of it and I'll let him, or possibly Ron, address that situation.)


    Quote Originally Posted by iandraz View Post
    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 some 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.
    Last edited by dhackney; 11-17-2010 at 04:56 PM.
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    Illustration of our frame failure and 3 point pivot frame load points:




    It is my opinion that our payload was too heavy for the stock frame when loaded onto the two points that were so widely seperated. In addition, the rear load point is located on the rear tapered section of the frame, which is significantly weaker than the forward sections of the frame, as illustrated below.



    Note that our frame was not reinforced, sleeved or boxed anywhere other than the fully boxed frame extension of 17.8" / 452.1 located at the bottom of the step-down section.

    A full discussion and photos of our frame failures, repairs, etc., is located here: http://www.expeditionportal.com/foru...ad.php?t=24225
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  8. #8
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    Default Payload and subframe mounting

    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,

    Quote Originally Posted by lehel1 View Post
    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/..._truck_frames/

    Doug

    ------------------------------------------------

    Quote Originally Posted by kerry View Post
    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.
    -------------------------------------------------


    Quote Originally Posted by iandraz View Post
    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.
    ------------------------------------------

    Quote Originally Posted by kerry View Post
    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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  9. #9
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    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/f...ionmodulus.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/f...cationinfo.pdf).

    Doug

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    Quote Originally Posted by lehel1 View Post
    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
    --------------------------------------------------

    Lehel,

    The Fuso FG is more comparable to the new generation UGN (U500 in the U.S.) rather than the classic Unimogs. The U500 uses the same basic design as the FG: ladder frame and standard drive train and suspension (no torque tubes). Obviously, major differences include coil spring suspension, GVW (33k) and the portal axles.

    I think you would find a separate suspension for a camper platform attached at the spring shackles would add unnecessary weight and complexity.

    In terms of spreading the load down the length of the frame rails, I agree that this method is the best possible solution to avoid hot spots, stress risers, etc.

    By bolting a platform rigidly to the frame, you limit or eliminate the FG frame's inherent flexibility, which is an important part of its strength. Think of the difference between a flexible tree that bends with the wind and a stiff tree that doesn't. The flexible tree survives a wind storm. With a rigid platform, the strength of the platform becomes the limiting factor for all stresses introduced into the frame. With the wet-noodle flexibility characteristics of the FG frame, this does not bode well for the long term survival prospects of said rigid platform.

    Consider instead a system that spreads the load across the length of the frame but still allows the FG frame to twist at will. Check out the system used by All Terrain Warriors and consider the use those FGs are subjected to, especially their commercial off-road tourist buses. I think they've got it figured out.

    I sure wish I would have known about those guys before we started.

    Doug

    ---------------------------------------------

    Quote Originally Posted by whatcharterboat View Post
    From the article quoting Toner

    Rigid mounts should be used at the rear and flexible mounts at the front. The front mount should not be at the front of the body.

    Toner said there are three basic types of body mounts: flexible, rigid, and combination. Rigid mounts should be used at the rear, and flexible mounts at the front.

    He said that even though U-bolt body mountings are popular, they are among the least effective mounting systems.

    “Are they bad by themselves? No,” he said. “But they don't tend to stay tight.”

    He said if they are used, proper frame spacers must be used. Some of the problems are loosening, not preventing forward movement of the body, and frame damage. He said frame flanges should never be notched for a body mount.

    “The body should not be rigid at the front,” he said. “It is better to be mounted solidly at the rear and float at the front. Avoid high moment areas for the mounting brackets. Use existing frame holes when possible.”




    I know I don't want to sound like a scratched record about not using pivot frames on FG's but could I just say that Toner's advice applies to these trucks perfectly. This works.

    Except the statement earlier in the article about moving the rear axle rather than extend the frame. I'm sure he didn't have a tapered FG frame in mind when said that. Obviously this guy is not just an engineer and has done his fair share of time on tools out in the workshop.

    Can anyone explain why this is the case?

    Kerry, when we see rigidly mounted bodies on FG's that have sustained damage, for whatever reason, it's always the front mounts that are the worst. Maybe a little damage in the middle and never at the rear. This maybe on trucks where the weight is evenly distributed too. That was how my boss started to develop our flexible mounting system nearly 20 years ago. By looking at where the mounts tried to tear apart and making the correct allowances. Not on road trucks but mainly eco tour buses and offroad work trucks where the frames are exposed to a lot of twisting and jarring.

    I presume your body has rails that sit along the chassis and they are u - bolted. Chip posted some pics months back (lost???) of a truck that had springs between the nuts and the flat bars of the u bolts so they had some give/stretch. Although I noticed in the pics that the springs were wound so tight that there was no movement possible anyway. But the intention was certainly there.Why don't you think about that if you're worried?

    As Toner says if you stay with the u bolts one of the problems is loosening > well, sprung u-bolts would be the same thing as a loose ones, so you also have to try and stop the body from moving sideways at the same time as allowing it to move up and down. The forward movement he mentioned should be prevented by your rear mounts.

    If (and only if) you are worried about damage, this will be infinitely easier for you to do than some of the alternatives being discussed. Mind you, I'm only going on what you've described about your truck but IMO this will be a much safer option too if done correctly.
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    Quote Originally Posted by whatcharterboat View Post
    Darrin must be a bit of a perfectionist , heh? Really good quality work from what I can see in the pics. If ever we have to sit a box section or channel ontop of a chassis rail (and this is rare), the Australian body builders guide gives an option of tapering the section up and away from the chassis at the ends instead of the "Frogmouth" ends. IIRC the taper has to be longer than the section is high and without looking it up, I think the angle is about 1 in 20.

    John
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    Quote Originally Posted by kerry View Post
    I'm not that worried about the mounting on my truck although I had considered the spring loaded u-bolt option. I'm more interested in trying to understand what is going on with frame stresses and body mounts. My attitude towards my own truck is almost totally pragmatic and un-theoretically informed. The service body has been on my truck for 10 years. I've seen no evidence of serious damage so far. There is evidence of a slight crack in the sheet metal at the front of the service body which was welded but that could have been caused by something other than frame/body interaction. I like the storage that the service body offers. I also like the fact that it can accept a truck camper. So I'm willing to experiment and see if the system holds up over time.
    But my example does raise some questions. From what I can gather most commercially sold FG work trucks don't have complex and elaborate body mounts. Why are expedition camper builders more focused on complex mounting systems compared to the commercial markets? I've seen the pictures with FG wheels on very uneven ground to indicate frame flex and how pivot mounts handle this flex. But my guess is that expedition FG campers are only rarely exposed to those kind of extreme frame flex inducing conditions. Is it wise to build for those conditions or do as the commercial body installers do? Or, if frame flex is something that should be considered under all conditions and not just extreme conditions, why aren't commercial truck body installers using pivot mounts of some kind?

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    --------------------------------------------------------

    Quote Originally Posted by whatcharterboat View Post
    If ever we have to sit a box section or channel ontop of a chassis rail (and this is rare), the Australian body builders guide gives an option of tapering the section up and away from the chassis at the ends instead of the "Frogmouth" ends. IIRC the taper has to be longer than the section is high and without looking it up, I think the angle is about 1 in 20.
    The pages related to mounting a body (payload) from the Fuso body builder's docs for the current generation trucks is here:

    http://www.hackneys.com/mitsu/docs/f...dymounting.pdf

    Note especially the last page regarding mounting on an FG.

    -------------------------------------------------------------


    Quote Originally Posted by kerry View Post
    Why are expedition camper builders more focused on complex mounting systems compared to the commercial markets?
    My somewhat flip answers would be:
    1. Peer pressure
    2. Too much time on our hands
    3. Being much, much, much (try infinitely) too overly focused on the truck prior to departure and subsequently discovering what it is all about
    4. Internet access to ExPo
    5. Trying to build a truck that is ideal for the entire planet instead of the 80-90% we could access with a VW Westphalia
    6. Building to handle conditions that we "might" encounter rather than those we are certain to encounter


    Based on almost two years of living out here, building a pivot frame and breaking the truck frame, my answers would be:
    1. With the FG frame, you really do need to allow for frame flex stresses on your payload if you are going anywhere other North American paved or graded roads.
    2. If you come out here, you will absolutely encounter conditions that will put severe stress on anything rigidly bolted to an FG frame, even on market town roads.
    3. Most (OK, almost all) North American Commercial Off The Shelf (COTS) campers are not built to the strength of a typical service body. If you are going COTS, you need to isolate that relatively fragile camper from the FG frame somehow.



    Quote Originally Posted by kerry View Post
    But my guess is that expedition FG campers are only rarely exposed to those kind of extreme frame flex inducing conditions.
    Real world, full-time overlanding is not about seeking out extreme frame flex inducing conditions. It is very different from weekend or vacation sport 4x4, etc. Most of your time out here is spent on market town roads going from one interesting place to another. Having said that, some of those market town roads would not qualify as roads in the U.S. Things are different out here in that regard.

    Quote Originally Posted by kerry View Post
    Is it wise to build for those conditions or do as the commercial body installers do? Or, if frame flex is something that should be considered under all conditions and not just extreme conditions, why aren't commercial truck body installers using pivot mounts of some kind?
    Like any good consultant (I'm still a card-carrying member of the guild), my answer is "it depends."

    If you know for certain you are staying in North America and you'll be on graded BLM roads, graded gravel or pavement, I don't' think you need to worry much unless you are using a COTS camper.

    On the other hand, if you are coming out here with a payload that is less than battleship over-engineered, strong and capable, then you should address the issue. You will definitely, without doubt, be put into conditions out here that will take the FG frame to its limits. If you don't want your camper taking those stresses, isolate it from the torsional rotation of the frame.

    If I had to choose, I'm a lot happier about breaking our truck frame, something you can get fixed literally anywhere in the 3rd world, than our camper, which would have been very challenging to repair.


    --------------------------------------------------------


    Quote Originally Posted by Tree View Post
    Our 98 FE has been U bolted with several different boxes. We bought it with a dry box, built our own wooden box for landscaping, and currently has a roll off system on it. Both boxes were U bolted and the frame shows no sign of damage, just beginning to lose some paint. I understand that frame flexes but so many rigs out here are u bolted. They dont ever seem to have a problem.

    Does the metal or whatever keep the frame in place or does it bend with the frame? Also lets say a flatbed is attached directly to a frame. The flatbed will bend with the frame, which damages the flatbed and frame... am I correct? But if you put it on some pivot mount, then the frame flexes by itself without any damage? Dang this stuff is intresting

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    Tree,

    Almost everything you will see in this section of the forum is related to the FG. I do not know how the FE frame compares to the FG frame in terms of strength or twisting characteristics. I have never read that section of the documentation. The FG frame is VERY flexible.


    Quote Originally Posted by Tree View Post
    But if you put it on some pivot mount, then the frame flexes by itself without any damage? Dang this stuff is intresting
    Click here to learn more about pivot frames: http://www.hackneys.com/mitsu/index-pivot-frame.htm

    As Kerry pointed out, for most service/work applications you wouldn't need one. Their primary purpose is to protect relatively fragile payloads such as campers from the twisting of the truck frame.

    Pivot frames are standard with Unimogs, as their frames also twist a lot.

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    Quote Originally Posted by whatcharterboat View Post
    Kerry,

    From what I can gather most commercially sold FG work trucks don't have complex and elaborate body mounts. Why are expedition camper builders more focused on complex mounting systems compared to the commercial markets? I've seen the pictures with FG wheels on very uneven ground to indicate frame flex and how pivot mounts handle this flex.But my guess is that expedition FG campers are only rarely exposed to those kind of extreme frame flex inducing conditions.

    Firstly most flat beds will flex with the chassis somewhat so the stress on the mounts will be less . I imagine a workbody like yours would have alot more rigidity and therefore more chance of damage to the mounts but as you say, you may only rarely be exposed to this kind of frame flexing. That's up to you.Weight will magnify everything but it sounds as though your body has at least been built as Toner suggests and therefore front mount damage should be minimized anyway.

    To cater for these extreme conditions or not??? We could keep going on about this forever. If you're not worrried then as you say, just wait and see. Good plan. The way your body is mounted , it sounds like IF any damage does occur, as long as you catch it early enough the worst thing should only be a u-bolt failure rather than a major chassis drama.

    Also most work truck/body builders would never bother with flexible mounting of the cost mainly. The customer wouldn't want to pay for it and often they aren't exposed to the stress anyway. Obviously there would be exceptions to this. Some of our rural fire brigade FG's have 4000litre (more than 1000gal) water tanks on them. Imagine the stress they're under when they fly through the bush to save someones property.

    Why are expedition camper builders more focused on complex mounting systems

    Also a camper body (especially a composite one) tends to be very stiff. Due to its construction and shape maybe even stiffer than say your steel workbody (but not as strong). Once you try to twist them with the chassis something has to give.
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    Quote Originally Posted by kerry View Post
    Thanks for all the advice and comments. My service body is attached with 6 u-bolts. Two at the front on the raised portion of the frame, two more not too far back on the dropped down portion and two more near the rear. Also, there is a short extension to the frame (10" or so) of steel channel associated with the step bumper. There is a piece of flat steel welded to the outside of that channel on both sides. It extends up alongside the FG frame about 8". It is welded to the FG frame and there is also one bolt on each side going thru the FG frame. There are two bolts on each side going thru the steel channel extension. The service body frame sits on top of a 1/2" piece of wood (oak?) on top of the FG frame. When I just crawled under there to confirm the attachment I discovered that the left front u-bolt is actually quite loose. I can move it around with little effort. The other u-bolts are tight, to the point of slightly bending the 3/8"(?) steel which butts up against the lower portion of the FG frame. None of the U-bolts have the wooden or pipe reinforcements inside the frame described in the body manual pdf that Doug posted.
    One of my concerns about spring loaded u-bolts is whether or not those springs will provide enough pressure on the frame to hold things in place. I've seen the one posted here too and I wondered how much pressure those springs provided compared to a non-sprung u-bolt. How would a person go about determining the appropriate size and amount of tension springs installed on the u-bolts would give compared to non-spring u-bolts?
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    Quote Originally Posted by lehel1 View Post
    i was just doing some research, came across dump beds on the fuso's. then laura reminded me that the truck we ordered susposedly has some reinforcement from the factory specific for adding a dump bed setup if we wanted in the future.

    i will call pioneer on monday and find out more on what this entails, my question to doug and others is does your frame have reinforcement frame plates located along the drop down curve behind the cab, ours frame does. it goes from just behind the cab all the way down to the straight section leading aft. i'll try and get a pic of this on here monday.

    the dump beds might be considered a 2 point system, will be interesting to find out more about these

    cheers lehel and laura

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    Lehel,

    Here are some shots of a brand new FG with a dump bed: http://www.hackneys.com/FG/chassis/index.htm

    You can compare those shots to these shots of our frame and frame extension: http://www.hackneys.com/mitsu/photos...ldup/index.htm

    I think what you are seeing is the stock step-down section that is joined by a seperate piece of channel.

    A step-down reinforcement properly installed for an FG will be plug welded over the step down section. Here's the relevent instructions from the body builders docs.




    RE: more thoughts on camper box suspension
    1. The more you spread the load across the length of the frame the better; this implies the more load points you have, the better
    2. Simple is good. Add simplicity until you have the fewest components accomplishing the goal possible.


    Your goals are:
    • Provide location between the camper box and the frame on all possible axis of movement, e.g., lateral, longitudinal and axial. That's a fancy way of saying the camper box stays where it's supposed to on top of the Fuso.
    • Provide for independent movement of the Fuso FG frame that does not load, stress or twist the camper box.


    Doug


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    One of my concerns about spring loaded u-bolts is whether or not those springs will provide enough pressure on the frame to hold things in place. I've seen the one posted here too and I wondered how much pressure those springs provided compared to a non-sprung u-bolt.

    Quote Originally Posted by whatcharterboat View Post
    Kerry, I imagine that the problem with sprung U-bolts (as I said before) will be sideways movement rather than moving fore and aft so you would probably need to add some sort of simple plate arrangement similar to the front of a tipper that prevents sideways motion but still allows up and down movement. That's the whole idea. That old example in the pic didn't look like he had catered for that, but I would, if you intend to go with the sprung Ubolts.

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    Here's a page from the Freightliner M2 body builder's docs that show the application of a shear plate when using a U bolt mounting system.



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    Quote Originally Posted by whatcharterboat View Post
    Doug, Not sure about that one in this case. If the back of Kerrys truck is fixed firmly at the back and we are allowing for some up down movement at the front I think the the shear plate bolts/holes would flog out.

    I was just thinking about something firmly fixed to the body that comes down alongside the chassis rails but is no way attached to them.

    And maybe tapered away from the chassis at the bottom so there is no sharp wear area on the chassis. It only has to guide the front of the camper

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    John,

    I am not qualified to offer anything other than posting the manufacturers documents on these issues.

    I think anyone who is considering doing this or wants to learn more needs to pick up the phone or send an email to Fuso engineering or talk to a local shop that does this for a living.

    My guess (note: guess) about the shear plate is that it is used to locate the payload longitudinally, meaning it keeps the tank full of water/fuel or load of rock/dirt or loaded concrete mixer or [insert payload here] from moving foward or backward on the frame if the U bolts are loose.

    The Freightliner M2 truck in the U.S. can be configured with a GVW of up to 60,000 pounds / 27,216 kilos. That's a lot of bananas.

    If you keep your U bolts tight it might not be required on a smaller load. Again, best to ask the pros, I am not qualified to do anything but post the docs.

    Doug


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    If you keep your U bolts tight it might not be required on a smaller load.

    Quote Originally Posted by whatcharterboat View Post
    BTW Remember we are talking about sprung U bolts here rather than the l shear plates associated with normal u bolts.

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