Finally Recovered!
Well, I finally had a long enough break after the big push to get it ready for the expo. (Was a bit burned out on the truck.) So I decided to get back at it. I have a Huge list of things to attend to but the first priority was getting the truck to ride better.
I was confident shocks were not the problem. After finally doing the research and crunching the numbers I determined that my spring rates were way out of line.
I have already rebuilt the leaf springs twice. The first time, I had read every post on the forum and determined that I needed to get the truck off the bumpstops to get it to ride better. I have outlined the process earlier in the thread, but basically I went from a 5 leaf setup in the front to 6 leaf and 6 to 8 leaf in the rear while removing the rear overload springs. This did help a bit on the bigger bumps but the ride was still horrible. Just before the trip to expo, in a last minute effort to improve the ride, I removed two of the shortest front leaves to make the front into a 4 leaf setup and still retain the ride height. This made it so I wouldn't hit my head on the ceiling anymore except on the really big bumps but it still rode like a Jackhammer.
When I got home I decided to brush up on the science of suspension. I discovered something called wheel frequency. This is the rate at which a vehicle will bounce if the shocks were disconnected. The math is a bit complex but luckily there are good calculators out there to save you the trouble.
http://www.racingaspirations.com/apps/wheel-frequency-calculator
Wheel frequency is what determines the comfort of a vehicle's ride. The front and rear of the vehicle need to be at different frequencies in order to make the vehicle ride flat over bumps at speed rather than wallowing. The ideal front frequency is about 1.35 hz for a passenger car up to 2.0 hz for a performance vehicle with the rear being about 20% higher. On a ten thousand pound Fuso this would mean approximately 500 pound front spring rates and 650 pound rear spring rates would be ideal assuming the weight distribution is even front to rear.
I found a nice leaf spring calculator here:
http://www.suspensionmaxx.com/tech-support/leaf-spring-calculator/ After crunching the numbers this is what I came up with:
The individual leaves are .4375" thick front and rear
The fronts are 46.75" long
The rears are 49.5" long
The original spring rates on the 2000 fuso are:
Front 5 leaf: 939 lb
Rear 6 leaf: 1127lb
In other words about twice what the ideal rate would be for a 10000 pound vehicle!!
After I added additional leaves to the front and rear I was at:
Front 6 leaf: 1178 lb
Rear 8 leaf: 1323 lb
Which not only made it even more stiff but also reduced the percentage of difference between the front and rear causing increased wallowing.
Removing two leaves from the front was a step in the right direction but not nearly enough:
Front 4 leaf: 785 lb
Rear 8 leaf: 1323 lb
With spring rates like that and 600 miles of dirt road on our last trip it really was a good "shake down" to see if the camper would hold together!!
Last weekend I redid the springs again and the results are finally what I would call comfortable. I ended up using the original main front leaf and the second and third front leaves from a 2014 Fuso which are parabolic. I put stacked metal shims between the leaves to decrease friction. I stacked steel plates under the leaf pack to achieve the ride height I desired. The rear ended up being a hodgepodge mix of the original main leaf and the top four leaves from a 2014 Fuso(I cut the eyes off the main leaf and used the next three.)
Front 3 leaf: 589 lb Wheel frequency 1.62 hz
Rear 5 leaf: 827 lb Wheel frequency 1.92 hz
The results are dramatic. The truck rides very nicely. It does lean a bit more in the corners but I believe that will be sorted once I make some spacers for the front Timbren bump stops.(they are designed incorrectly for a 2000 model and don't make contact-ever.) I can finally feel the shocks doing their job. A 2 leaf front setup and 4 leaf rear would have been even more compliant but I like the extra security of having an additional leaf in the front in case one of them breaks. I would consider having custom springs build to my own specifications at some point using more leaves and a thinner material to increase articulation but for now the ride is nice enough that I would consider hopping in and driving to Alaska or Argentina at the drop of a hat..... FINALLY!!! It has been a lot of work but worth it to avoid having to pay nearly $8000 for a custom setup-by the time they install it. I spoke with one gentleman that had spent over $10k on his! Always more fun to do it yourself!
Allan