Wow! What a long lived and great thread! And yes the caster problem probably exists on all cutaway an incomplete chassis of many different makes and capacities (Sm, med, lg), unless the fitter reset everything after completion which I have found to be rare. I worked as a Ford Tech, Fleet Tech, and a FD Tech back in the 90's and I was ASE and Ford Certified in suspension. When the cutaway is new and shinny with new unsettled springs with no load, the factory will set the alignment for that condition. Have you ever walked around a dealership and seen new dual pickups with the bed off and how high in the air the rear frame sits? Well when a load is placed on the back and the rear of the truck settles as the rear approaches the ground the frame and suspension rotate around an imaginary arch with the front axle being the origin. This causes the caster to become less positive in most suspensions. As discussed before, the right amount of caster makes vehicles track strait. Well this rotation can easily knock 2-3 degrees of of a caster and take it to a minimal setting, which when a force is applied by a passing vehicle or a wind gust can case the suspension to be compressed and momentarily force it out of spec which is the reason to try setting the suspension in the middle for a specific load, so these sudden impulses do not push the suspension out of spec so easily.
Another aspect that is worth looking into is the ride height specification. Each chassis has an optimal designed ride height, at this height, changes in the suspension geometry (bumps, wind gust, etc.) have the least impact on handling, as the ride height increasingly differs from the optimal "designed" ride height, these input have a more drastic impact on handling. Correcting any ride height issues should be one of the first items before setting the caster, camber, and toe (they will change again if you correct the ride height). I would also check for frame squareness while performing these adjustments. This is especially important if your rig has a cut frame with an extension. Ride height will change over the years as the springs settle, unless you have an air-ride with an auto-adjust feature. While you are at it make sure the following are in great condition: ball joints, tie rods, drag-link, steering-box, bushings, shocks, tires, etc. are all in good service.
Everything can be adjust to spec, if the sleeves do not get the +4 to +5 degrees of camber, (my target would be 4.5 at the specified ride height) you will likely need a frame shop to adjust the axles with a press. There are shims to adjust the camber and toe is the last adjustment.
I am a huge fan of the air suspension and it is on my upgrade list, for my 2006 31' E450 Fleetwood which is starting to squat in the rear and wander the road because the alignment is now off. It is too harsh on washboard roads and rough highways, it feels like it is damaging my coach. I am not talking about the add a air springs for the back but a complete retrofit to air springs/bags. We performed these modifications to our ambulance fleet (Chevy) and the difference was dramatic over the spring based buses. If I were a patient, I would want the aired setup
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Poly bushings should replace all rubber after 5-10 years. They last longer and 5-10 years is about as long as rubber ones stay the correct hardness. Shocks would make a big change in ride and drive-ability (it sounds like Koni has the hot setup), then sway bars, I think the poly bushings on the sway bars make a bigger improvement than the larger diameter bars, so if your budget is tight, look at replacing the rubber bushings with poly. Note the front sway bar settles the rear and the rear sway bar settles the front.
The steering damper would be the next upgrade, then finally the rear track bar.
I have heard that vortex generator on the rear help with gusts and passing vehicles, but this would be my last step. Well, if money were no object, there would be one more last step and that would be an active suspension on the shocks like the new Corvettes and Cadillac s have on them, but I have never seen them for this large of a vehicle, so we would be in the experimental category. If all of this was done, handling would be a dream. If you did any of this starting with ride height and suspension alignment, you would be happy.
Happy Travels!
Great thread!