frame flexing, suspension travel, and weight transfer

[Mundo4x4Casa]

In my later years, I've continued my life long penchant for not leaving 'good enough' alone when it comes to four wheel drives. I did my first springs-over-axle in 1965 on a 1949 Willys Ute Wagon, during an era when there were few willing to try it or even knew what it was. Those pioneer days are long gone. Here it is by 1968:

Subsequently, I completed a lot of SOA's on leaf sprung 4WD's of all stripes and learned a lot about suspensions along the way. Three of my victims:


My hard core jeeping days are over, but I still maintain a Dodge pickup with stuff and a hard side Lance camper. This rig is now my focus. Here it is on the Mojave Road:

And a current config:

Background: I would like to install a long arm 4-link kit to the front axle to increase the suspension travel and solve my current caster woes. For more background, view this post:
http://truckcamperadventure.com/2017/01/extreme-truck-camper-drivetrain-build/
This would include softer, incremental rate lift coils with heavy shocking. Currently I have a 3 inch 'puck' lift on the short arm front axle. The reason for a quest for more suspension travel is to transfer less torque to the frame, and subsequently less frame twisting. I suffer very little frame twisting now with a short bed, hydro formed frame of the era, but I want even less frame twisting. The rear axle would remain as it is now with little suspension travel when loaded. What you are looking at is the factory camper package with one thicker upper secondary; an anti sway bar; two added upper secondaries from a one ton; a 3 inch lift spring; and Stable Loads to successfully haul my 2650 pound load off road. My idea is to solidify the rear and free up the front effectively pivoting on the rear axle.

With all this in mind, my questions are:
1. How would softer, longer travel coil springs in front effect the weight transfer when hard braking?
2. Are there other down sides I'm not seeing?
3. What, in your opinion, are any other unintended consequences to this 'soft front/hard rear' plan?
I hope this becomes a physics discussion and divulging of experience.
Even if you have NO experience with this, give me your best shot.
regards, as always, jefe (aka: jeff reynolds)

 

[1stDeuce]

1. Softer springs will dive more under significant braking. This can be countered with some anti-dive geometry on the front suspension. They'll also lift more on acceleration. Nothing you can do for that. Your short arm setup has some anti-dive due to jacking, but not a lot, and that jacking causes the axle to move forward and up, making bumps a bit more harsh.

2. There is one big problem that I see... You're ride will probably not be very good with really soft front springs and stiff rears... Two reasons: First, the ride frequency split will be well out of whack. This means faster running will probably bottom the front easily, even with multiple shocks and more travel. Do a little reading on proper spring rates for correct ride frequency split, and see what that tells you. You might find some good reading on AEV's forum... The second reason is that you're basically turning your truck into a three wheeler, with almost no roll rate contribution from the front, but lots from the rear. Rather than the body of the truck moving as the average of the roll of the front and rear axles, your truck will roll as a match with the rear axle only. Actually, it'll probably move MORE than the rear axle, due to the high CG of the camper. Basically, your truck will rock from side to side following the rear axle only, instead of rocking only half as much as each axle individually.

3. I think that covers the ones I can think of...

The only real way to eliminate frame flex is to make the frame stiffer. Honestly, the frames on your vintage of Dodge didn't flex that much... And the flex that does happen doesn't cause any issues that I'm aware of. I think you're chasing a losing battle by try to make a virtual 3-wheeler so that you don't see any frame flex. Not a good plan, IMO.

If you want a ride improvement, you likely need to soften the rear, and stiffen the front, so over any given bump, the front isn't articulating much more than the rear.

BTW, If caster is low on your truck, and your lower cams are already maxed out, you can put in some offset upper ball joints to gain some caster. Redline uses them in his Dodge and they work well.

 

[Meili]

Before making changes, fix the first big problem, frame flex.

Tie the cab to the bed/camper, eliminating one variable. This will allow the suspension to do its job.

I know its on the much smaller scale but I did this on mu S10 and the difference is really night and day.

Can't build a castle on sand!

The braces were built to spread the load more evenly across the sheet metal. If you decide to do this and have access to a welder I have a better way of doing it in mind.