Spring Mounts for Rail-on-Rail Subframe

DiploStrat

Expedition Leader
#16
Neil - been there, done that: http://www.pbase.com/diplostrat/image/103074598

At one time some Aussie overlanders camped out in my driveway in Douala. They paid "rent" by starting at the front of my truck and tightening every bolt.

N.B. I have never heard the term "bellville spring" but the picture that Jon posted from MB is exactly the "pull out" mounting that I was describing. For overland use it usually has about 4-6 inches of possible travel.
 

Mundo4x4Casa

West slope, N. Ser. Nev.
#17
Diplostrat,
You are one of the most knowledgable and articulate people on here. I perused your website and enjoyed reading about your colorful life . Without speaking CAR-ease, you are speaking my language. I too was one of the 'first world jeepers' who obsessed about torsional issues with a wood frame Lance truck camper well strapped down to my short bed truck. I have now come all the way around to your thinking, which is a light, short bed camper box on a Chevy or Dodge one ton platform has very little torsional issues. Besides adjusting the tie down torque to fit the situation; loosening the rears when I think the frame is going to twist, I don't need much adjusting. Here is a pic at near maximum axle twisting: very little change in the attitude of the 'box', i.e. very little frame twist, and no damage which has been widely predicted:


Ford platforms with their penchant for frame twisting needs extra help to keep the twisting frame from pulling the camper box apart.
Here is a short vid of my ride up the Diablo Drop Off, a 100m blow sand dune with my current setup: 20 pounds of air in tires; started in 4th gear/low range, downshifting to 2nd gear/low range for the deep moguls near the top. The front/rear True Trac differentials were superb and transparent in delivering power to the wheels with traction, not the other way around, even with a wheel off the ground.
https://www.dropbox.com/s/bfj5y93wsd7vfkw/jefe does sand hill at dry wash of the devil Anza.m4v?dl=0
In a long bed format, the 'pull out' springs at the front or rear, not both, of the bed would help mitigate the stress. US military trucks from the 1950's on use this method. All the heavy camper boxes above, by shear weight and length of frame have twisting, some models massively so, that have been or need to be addressed usually by the manufacturer.
The washboard issue of which you speak is alive and well in the Desert Southwest, U.S. I've been on thousands of miles of washboard and use the air down method to allow the tires to take more of the suspension's job and kill the bad vibes. My brother, who won the 1st King of the Hammers off-road race in California believes the secret to washboard road running is to air down and go faster, not slower, kind of like the lifting of a power boat at speed. Running at much lower pressure we had a couple long, straight, horrible sand based washboard roads in Death Valley that we traveled @ 100kph in a pair of 4.5Kg rigs to good avail with a hanging dust cloud as far as the eye could see. I followed him @ 10km distance.
jefe de doble traccion.
 
#18
Running fast aired down works great, until you see potholes across the track. Then you can eat the pothole or go through massive vibration trying to scrub off speed. No fun in 10 tonnes of camper!
 

Mundo4x4Casa

West slope, N. Ser. Nev.
#19
Joe, agreed about the pot holes or cross washes. It is a crap shoot, but we knew from experience the road was well graded. You really drive well ahead of yourself with a laser focus at that speed, even with a couple 6 ton campers, weaving from one side to the other trying to find the smoothest surface. I've found the smoothest surface is at the extreme edge in the opposite lane of traffic flow; something about the shape of the washboard sand. We could see a few civilians coming in cars well ahead and all of them just pulled to the side at the sight of next coming of the motorized haboob.
One reason for having a narrow camper:

jefe
 
#21
A lot of good info here, thanks guys. Would anyone happen to know how to calculate the required deflection rate for the springs? I know Neil says to try and plan for 100mm, which I think is good advice. I have seen subframe separation pictures and then when I see a lot of the springs used they look to be too short to allow for that separation. With the long springs on Cloud9 it looks like they could handle the 100mm. Will have to look on our chassis if I have that much room below the spring mounts (they were already on the frame). I know the springs washers that came with the truck would not allow for that much movement,at most 25mm.

I also see on Cloud9's subframe there is a short vertical channel in the front to keep the subframe aligned. Looks to be a good idea but have not seen that on all of the subframes. I currently do not have that planned with the fabricator but may just add it. I do know the previous subframe did not have it, but the spring bolts were much shorter. Also the previous bolts were M16, which I am planning on using again (maybe use 5/8" to make getting the springs easier though).
 
#22
Why not use airbags. BIG airbags, the type used on Class 8 trucks?
Airbags for suspension, and airbags between frame and cab/body.
No reason not to use airbags, we have airbags in the rear. The bags must have a long enough range of motion to handle suspension travel, this can be hard to find.
This sort of suspension work needs to be engineered by a qualified person. The forces involved are very large.
 
#23
Jon

Dont forget to leave sdequate clearance between the vertical guides at the front and the chassis. These to will deflect and if too close will foul with the chassis.

Neil
 
#25
Thanks again Neil, will keep that in mind if I decide to add them. The major welding is now complete with just the hardmount plate in the rear and spring mounts left. The current plan is for it to be finished tomorrow.

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