pivoting frames and mounting campers

pappawheely

Autonomous4X4
If it has, it will probably be in one of Biotect's posts. I kinda skimmed thru those as he gets pretty technical, figuring i would get to them when I had enough time to thoroughly digest it. But there is a lot of good stuff here.
On thing I noticed being mentioned more than once was the use of old valve springs for mount springs. Any engine machine shop will give away old valve springs, as they are scrap to them.
I know several engine builders but it seems to me that if the springs are toast, they are toast. I usually love anything that has the word "free" attached but not if it is no longer functional. I can get the spring specs, (wire dia, # of coils and height) to figure the spring rate of new springs. That might get me in the ballpark but it would be nice to benefit from some first-hand experience. I am blown away by the amount of engineering/design analysis available on this site. The old Nike phrase comes to mind; Just do it!
 

Gatsma

Adventurer
Even though the springs might be "past their prime" engine-wise they will have sufficient compression for the purposes of springing a truck body mount, which ain't rocket science. If a bit too mushy, give the nut holding them a few turns. BAM! problem solved! Spring requirements for truck body mounts is NOT an exact science, guys. And if one should break, well, at the price you got them for, carry a spare or two. Don't worry, it won't throw off your weight OR center-of-gravity calculations. Just don't tell your friends...
 

Alastair D(Aus)

aging but active
spring rate

Papawheely !!!!!!!!!!!

Look at at posts by SkiFreak or go to his build web site at
http://canter4x4.com/

I am building a box on the back of an Isuzu NPS 300 - like a canter. I have used spring based mounts like Skifreak's but have fish plates (rigid plate) mounts at the back where there is essentially no twist b/n the sub frame and the chassis. This gives strong front/rear location. There are 3 spring mounts on each side. I used custom made springs that have 50mm possible compression at 20kg per mm. My initial loading is to compress the springs 15mm leaving 35mm movement for the relative movement.

How did I come up with these numbers? I looked at other trucks that had spring mounts, played with valve springs to see what they did, and then found that one company was using 30kg/mm on their mounts. I thought this was too high when you consider the loads at possible chassis/sub frame separations and went for 20kg/mm.

As said above none of this is an exact science and some playing around is necessary as well as backing your own judgement. If I have it totally wrong then something will break! I will then have more data to work with !!!!!! I have all digits crossed that I am not too far off.

cheers
Alastair
 

Goingbush

New member
Alastair,

Fish plates are actually an ADR requirement here, I didn't read the Truck Body ADR's until I'd almost finished building my box - I think they are really more to keep the subframe from dislocating in the event of an accident, but good insurance incase of a spring bolt fail. I have teflon (kitchen chopping board) on the sides of my fish plates incase of rubbing - but all good so far.

Ive done 12months touring now 36,000km and there are no loose screws or rivets and Im very happy with the subframe mounts on my Iveco 4x4 , On the front I used the standard Iveco spring washer packs and on the rear I used compression springs from Bunnings and its all working perfectly, have been over some very rough ground, there are no creaks, groans or thumps even when fully crossed up. The box on my Daily 4x4 dual cab is only 2.1m long . 2m wide so not as heavy duty as most of you are needing but if I was doing the job again, or even on a bigger rig I'd use the same method next time. Keep it Simple works for me.

Not sure if Spudboy has posted a link to his MAN 4x4 , theres a pic of his spring mounts on this page
http://daviddeere.net.au/dnnd2/en-us/Blog/Post/293 the top bracket has a hole in it (between the springs) there is a pin fixed to the bottom bracket , this locates the subframe making fish plates redundant - good idea !! there are a number of these spring sets along each chassis rail.

more here http://daviddeere.net.au/dnnd2/en-us/Blog/Post/260/Attaching-the-canopy-to-the-chassis
 
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pappawheely

Autonomous4X4
Thanks guys, excellent info. I will be jumping off, not just camping for fun. I would rather not go through a painful learning process if it's not necessary. That's what I love about this site, the wealth of first hand information. I worked in the engineering field for years and learned that real world results often differ from theoretical ones. I could "figure" a spring rate but without actual testing, it's still just an educated guess. I like the pin idea. That would be very easy to repair in the field if needed. My F350 frame twists like a wet noodle; its going to be moving a lot.
 

deminimis

Explorer
Quick question for the big brains on here. Looking at redoing my flatbed mounts sooner than later. I'll be using a setup similar to a M35 (springs and brackets (perches)). I've got that all pretty much dialed in (in my head anyway). My question relates to the rear attachments (left and right side). When looking at M35 schematics, it appears all that is used is a solid mount (brackets w/ bolt, no spring). At first I thought this odd, then I thought it makes sense as there really shouldn't be much flex at all at the rear of the frame as it is aft of the aft spring hanger. This rear m35 solid mount is the same regardless if it is a short of long cargo box. Don't have a M35 handy, so I can not verify this myself and I can not find a pic of the rear mount on the web. Sure would make things easier if I went this route at the rear. I was thinking I'd need a pivot at the rear, but doesn't look like it (if M35s don't need it, I think I'd be okay). Also, I will have a Superhitch Magnum hitch (4" cross tube) spanning the rear frame, so it really will be very solid back there. Thoughts? Thanks.


Here's an added bonus (in case the info is not already buried in here somewhere): The M35 part numbers for the inner and outer springs are 5360007372793 and 5360007372792. I'm starting with 8 pairs and I'll reduce from there if needed.


Well, perhaps I can answer my own question. I've looked at this pic several times (it's on here, there, everywhere), but never noticed the rear mount until now. Sure enough, it does appear to just be a solid mount (bolt and bracket) at the rear. Still, any input would be welcomed.

 
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tamangel

Adventurer
Don't have a M35 handy, so I can not verify this myself and I can not find a pic of the rear mount on the web. Sure would make things easier if I went this route at the rear. I was thinking I'd need a pivot at the rear, but doesn't look like it (if M35s don't need it, I think I'd be okay).
head over to Steel Soldiers ( http://www.steelsoldiers.com/ ) you can get any info you need on M35's might have to join to see pic's but no cost.. Excellent info available..

Mike W

*******
 

IdaSHO

IDACAMPER
I had the truck in the shop today doing some tests.

I had hopes that I could extend the flatbed headache rack over the cab to provide some between cab and camper stowage, but it proved unwise.
Adding in the amount of flex shown between bed and cab, I have less than 5 inches to work with. To slim to be useful. Still, I may come up with something yet.


Anyhow, it did provide for some flex test photos, showing just how well a simple 3-point pivot setup works.
Ive been running this setup for a couple of years now, and have logged nearly 50k with the camper loaded.

This truck for all intensive purposes has stock suspension, so no crazy amount of flex.
But I did get it flexed far enough that a hair more lifted a tire. So this should be as far as Ill ever have it flexed.

notes:

10 inches under drivers front
8 inches under passenger rear

I added some red lines in photoshop to illustrate the bed-chassis and bed to cab changes





 

tamangel

Adventurer
any idea how long the cab to end of frame measurement is on that Iveco? I like it..looking at a 12' frame truck currently but need a flatbed that will need to take a 14' Alaskan non-cabover..I guess the frame doesn't have to extend the full 14' but the flatbed does..

Mike W

******
 

IdaSHO

IDACAMPER
Pretty incredible.

Looks like the bed and cab share a coil sprung frame, on top of the chassis....

Then the bed is on a pivoting frame, on top of that :Wow1:
 

nick disjunkt

Adventurer
Pretty incredible.

Looks like the bed and cab share a coil sprung frame, on top of the chassis....

Then the bed is on a pivoting frame, on top of that :Wow1:
It's interesting that the fabricator didn't chose just to use just the 4 point pivoting mount. It undoubtedly isolates the body sufficiently on its own, but perhaps they were worried about it concentrating the load too much on chassis. I'm not aware of Unicat or any other similar companies having chassis problems caused by not using additional chassis rails. The secondary rails (sprung at the front) is undoubtedly the system required by Iveco's body building guide, but with the torsional isolation of the 4-point mounts, I would have thought the springs could safely be left out. Perhaps they were worried that hard mounting the secondary rails would make the chassis too stiff and prevent twisting?
 
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