Frame flex and type and kind of spring?

[Flameffects]

I have read as many forums, blogs and web pages as I can find regarding FUSO frame flex. It seems the 100mm or 4" is the max. I am getting to the point within the next few days that I need to fab the frame attachment points. Please speak up with your numbers.

There are many choices of spring configurations found on the internet. I really would like any pointers that you might have on the type and kind of springs that you may have used.

 

[dlh62c]

There are many choices of spring configurations found on the next. I really would like any pointers that you might have on the type and kind of springs that you may have used.

Yes there are. Using those as examples, you should be able to come up with a design that makes it your own. Designing and building the mounts are half the fun. Mitshibisi has body builder guides on their web site that will prove useful. It's that stinking step up on the frame that makes things problematic.

 

[SkiFreak]

If you plan on having a pass-thru then allowing 100mm separation will likely be problematic.
In my opinion, which I have detailed many times, is that the springs need to allow some separation of the subframe and chassis but it also need to restrict it too. Too much flex is as bad, if not worse, than having a hard mounted body.
My own setup allows for 30mm of separation.

 

[Flameffects]

Yes there are. Using those as examples, you should be able to come up with a design that makes it your own. Designing and building the mounts are half the fun. Mitshibisi has body builder guides on their web site that will prove useful. It's that stinking step up on the frame that makes things problematic.

I am looking forward to building the mounts. I still am not sure how much spring I need. There are lots of choices out there and so I prefer to not have to try to many springs.

 

[Flameffects]

No pass through for me. I am building a flat bed with a removable box. I weld for a living and need the truck for my work. My finished box will be much like a toy hauler because I love my motorcycles.
I still have no one tossing me a bone on type and kind of springs?

 

[Alastair D(Aus)]

spring mounts

It is some time since I dealt with this on my build but the following is what I recall.

I looked at available springs and found nothing available in the size I wanted. I tested a few old valve springs but found they varied a lot in tension and did not have the compression length I wanted.

I decided on using springs that would fit around a 12mm (1/2") HT bolt, and have a total compression of 40mm with a tension of 20kg/mm. I screwed the nyloc nuts down 10mm initially giving a preload of 200kg at each of the 6 spring mounts. This leaves a further 30mm before the mounts become rigid. I have fish plates - rigid mounts at the rear to restrict the front/rear movement even though the spring mounts themselves restrict f/r & l/r movement. I had the springs made at a spring works to the above specs since I could find no ready made source.

How did I come to the above numbers? Looking at what others had done, doing some simple calculations on what was needed to limit movement and just a gut feeling. I have not done any rigorous testing but so far it seems to be ok. I will not really know until the build is finished and it goes over some real lumpy roads.

cheers

 

[seancampbell]

I'm in the same position.

I'm getting ready to build my subframe and mounts and would like to have springs sourced before I go any further.

If you locate any or are thinking of getting some made I would be happy to share the cost.

sean

 

[SkiFreak]

There are a few companies in Australia that will manufacture custom springs.
I used Industrial Springs in SA for mine and the guys there were very helpful in determining the spring rate for my setup. Mine are heavier than Alastair's, being 31KG/mm, but I do have a pass-thru and, as mentioned previously, need to limit my movement to about 30mm.
What spring rate you end up with can only be determined by the design of your own build. I'm sorry, but there really isn't a "one size fits all" solution here.

 

[seancampbell]

Thanks SkiFreak,

I use your site all the time for my inspiration and your detailed information on parts and technical details.

 

[SkiFreak]

I thought I would share my ideas on how to size springs for mounting a camper to a FG frame.

So... what spring rate and range of motion did you end up with?

 

[trackadda]

i am searching for springs for my 2007 nps300 izuzu build and found this thread, does any one know of an off the shelf spring and where to get them now days. i am down to a local body builder and truck parts supplier to try but would be good to be able buy something that others have used and found works

 

[SkiFreak]

There is no "standard" spring, as the variables are way too vast.
You need to work out roughly the finished weight of your camper and how many mounts you will have, as only then can you do some math and figure out the spring rate you will need. You also need to determine how much separation is acceptable between the chassis and subframe, as this will be needed to specify the "safe" compression of the spring. For people that do not work with springs it seems counter intuitive, but the more coils a spring has, the greater the spring movement.
When you know all of the above information (as well as the desirable physical spring size) you can contact a spring company and ask them if they have a suitable spring available. if not, you will probably need to get custom springs made.
Just remember... you are not limited to using one single spring per mount. I have seen many installations that use two smaller springs to achieve the same effect.

 

[steve66]

Hi Tracka,

Thanks for opening an old wound for me


I reckon I've stressed/pontificated more about the subframe mounts than any other aspect of my build. The ex aircraft engineer part of my brain says this is a critical aspect of the design. But once you read everything available and look at a few in the flesh it seems that anything goes.


I ruled out 3 (or 4) point systems long ago, all the pro builders in Oz for these trucks use spring mounts, I see Gait has just converted his from pivot to springs but not sure why. I had spoken with Skifreak but didn't get to Industrial Springs before they closed down.


There doesn't seem to be any consensus on spring rate, some just chuck in whatever fits, ATW use the same springs for all builds, some guys use old truck valve springs, some of the photos you see of home builds appear to use very light springs HOWEVER I've never yet seen a report of anyone breaking a spring so eventually figured it can't be much of an issue in real life.


Decided in the end I wanted springs that were 40mm O.D, 40mm compression, 20kg/mm, length about 150mm. Just sounded about right!


Now the fun bit. Last year I contacted 8 spring makers in OZ, out of the 6 that responded 2 said can't be done, one wasn't interested, everyone said that 20kg/mm was a very big load on such a spring. Would not be a 'happy' spring they said. There was about 300% difference in prices as well, Hmmmm, had me worried again. put it back in the too hard tray.


Last month I had to decide as it's holding me up. Ended up going with Boynes Springs from Perth, they should arrive this week, 8 custom springs for $407 delivered. Their design sheet gives me about 30 mm compression before the spring enters the highly stressed zone. I consoled myself by saying I can always swap them out if need be, but doubt I will need too.


Am planning on 4 mounts each side but may end up with one as solid, depends on what my engineer says when he sees it. ATW use all springs, some guys have the rear most mount as solid, SLR have their solid mount above the rear axle, so again anything goes it seems!


Ahh, I feel better now Good Luck!


Cheers Steve

 

[skippythedog]

springs

I have no idea about the criteria for the spring mounts for campers ( I have a dump flatbed on my FG and use it as a daily driver).....but have you ever checked out the spring mounts used on commercial gas tanker trucks and trailers? Beall in Portland can probably help you or give you some idea about ratings/parameters. If there's nothing on the shelf, there are many spring places that can build anything you want.

 

[SkiFreak]

does any one know of an off the shelf spring and where to get them now days.

If you get stuck, you could always contact ATW, as I am pretty sure they will sell you a set of the springs they use for their builds.
Probably not the cheapest option, but it is an option.