93 F-350 4x4 Flatbed.......Where To Go From Here?

[IdaSHO]

Good way to do it.

Now take that measurement and multiply by 2

That's your total flex in the length of that bed.

And just about as much as I figured you might have.


If you are looking to put a camper on it, you have some engineering to do, if you dont want to twist it into pieces.

 

[grotto]

If you are looking to put a camper on it, you have some engineering to do, if you dont want to twist it into pieces.

Not what I wanted to hear, but not unexpected. Been thinking about pulling the bed and changing a few things anyhow. I appreciate the feedback. I've always run basically stock vehicles so this is all new to me.

Is it typical of flatbeds to flex more than standard truck beds? I suppose it depends on how the flatbed is built. So I guess it's either a pivoting mount for the bed, or one for the camper. Got me some research to do. Any tips, ideas, leads, links, etc. would be appreciated. In the meantime, I'll get going on basic maintenance.

 

[IdaSHO]

Regular beds flex just as much, but the mounting techniques allow for a LOT of movement.

A regular bed contains a camper with the bed rails and allows the camper to rock around.
While not ideal, it does work and has for decades.

A flatbed needs the camper rigidly mounted to the bed.
So you must allow the chassis to flex independently of the bed.

Ultimately, that is the best option IMO.

There are other methods, but I will always side with a 3-point pivot for "light" duty flatbed trucks and campers.

 

[pappawheely]

http://www.expeditionportal.com/for...s-and-mounting-campers?highlight=pivoting+bed

 

[IdaSHO]

def a great thread for reference.


BTW, Ive got my truck in the shop this winter for a ton of overdue maintenance.
Including cab bushings (YUCK)

To do that Im removing the bed. When removed Ill snap a ton of photos to show you exactly what Ive done.

Honestly, it performs better than I ever expected.

 

[grotto]

def a great thread for reference.


BTW, Ive got my truck in the shop this winter for a ton of overdue maintenance.
Including cab bushings (YUCK)

To do that Im removing the bed. When removed Ill snap a ton of photos to show you exactly what Ive done.

Honestly, it performs better than I ever expected.

Excellent.

I skimmed the linked thread and did a quick google search "flatbed 3-pt. pivot mount" and your old thread on Pirate 4x4 popped up. Was hoping you'd be open to share what you did. Even better that you seem quite satisfied with it. I'd rather not re-invent the wheel if I don't have to.

 

[IdaSHO]

After said and done it seems easy to say that it is "simple", but I know better.


The design and thoughts behind the pivot mounts are simple.

The execution and doing it right is another thing.

Still simple, but certainly takes some know-how to do it right.



So far, I have yet to find a reason to do it any different.

Although tearing it down far enough to inspect things after few years and
5,000+ miles of on and off road might provide me reasons to alter things.

I doubt it though :ylsmoke: And Ill keep you posted.

Ive got a bunch of parts on order for the tear down, to address a lot of small repairs / upgrades.

Once all on hand the truck will be in the shop. And removing the bed to do the cab mounts is task #1

 

[IdaSHO]

Here you go...

Some photos from the rehab, when I modified the flatbed for the 3-point pivot

All pivot points uses large press in bushngs.

Front mounts are on a cradle, supported by oak planks, and large U-bolts to fasten to chassis.

here are some shots from today, when I removed the bed

Arrows show pivot points. Two in front, one in rear

Rear

Front

Underside of bed, rear

underside of bed, front. Notice the black rub/impressions on the wood.
More to note about that later...

And where the front mounts were rubbing the wood. We did have some squeaking. This must be the source.
Ill grind these areas a bit to provide clearance.

 

[Schitzangiggles]

So pardon my ignorance, but how does the 3 point act any different than simply using rubber bushings/bed mounts but in an overly complicated and point loading manner?

You have a front to back pivot point at the front of bed and a port to starboard at the rear. Seems like a weak 3 point attachment system with little flexibility. Leafs springs use a shackle to account for the change in length as the spring cycles, but your set up from what I can tell doesn't account for the change in length as the frame twists and cycles other than what the bushings can deflect.

So what is gained by this kind mounting system?

 

[underdrive]

So pardon my ignorance, but how does the 3 point act any different than simply using rubber bushings/bed mounts but in an overly complicated and point loading manner?

You have a front to back pivot point at the front of bed and a port to starboard at the rear. Seems like a weak 3 point attachment system with little flexibility. Leafs springs use a shackle to account for the change in length as the spring cycles, but your set up from what I can tell doesn't account for the change in length as the frame twists and cycles other than what the bushings can deflect.

So what is gained by this kind mounting system?

Over the length of the bed even a small twist in the frame will produce noticeable vertical deflection of the frame rails between the front and the rear ends of the bed. A bushing can compress only so much, once that point is reach you are again forcing the bed to do things you're trying to avoid. If you are concerned with high point loads in only 3 locations (I'd say depending on what's loaded on the bed that can be a VERY valid concern) you may want to consider adding low-profile air bellows alongside the frame rails and connecting them together in pairs left to right - as the frame twists the air will shift from side to side as needed but the overall pressure in the pair of bellows will remain the same and thus load carrying capacity does not change. Seen this done in a Class-8 truck with a very long wheelbase, the frames on those twist something fierce as their rear suspension usually has next to no articulation to prevent high-COG loads from inducing enough body roll to flop the whole thing on its side. Basically the front and rear bushings located the platform onto the frame, and the several pairs of air bellows supported the load on it. Not sure how well it actually worked, but the theory seemed sound, and the owner was pretty happy with it...

As far as change of frame length as the frame twists - I sure as heck hope the frame rails do NOT behave like leaf springs in that department!!! Can you please come up with some numbers to support your claim that IdaSHO's setup is weak and inflexible? I'm just curious as to why you think he needs to be concerned with frame length changes...

 

[IdaSHO]

For starters, as the chassis twists, the distance between the front pivots and the rear pivot DOES NOT CHANGE.

It stays the same. The chassis is twisting, not deflecting like a leaf spring.

As for the rest of Schitzangiggles post, I dont know what to say.

The setup is a proven setup.

It is simply a "4-point pivot" without the front pivot.

If the chassis did deflect like a leaf spring, the following 4-point that has been used for decades would not work AT ALL.

 

[pappawheely]

I have thoroughly over thought this and have decided the design I like is the box resting on the frame as much as possible and spring mounts that allow the frame to drop away when twisting.

 

[IdaSHO]

Which is fine. It is another tried and true method.

Although it doesnt allow the bed to float nearly as freely as a 4 or 3 point pivot, as it is always in tension via the springs.

I avoided it due the fact that with that method, the bed is literally floating atop the chassis, not rigidly mounted.
I also fear the potential for the setup to become "dislocated" in some way. As in, doesnt return to its locating saddles at some point.

For me, the 3-point pivot removed those fears. Regardless of how unfounded they really are

to each his own.

 

[pappawheely]

Which is fine. It is another tried and true method.

Although it doesnt allow the bed to float nearly as freely as a 4 or 3 point pivot, as it is always in tension via the springs.

I avoided it due the fact that with that method, the bed is literally floating atop the chassis, not rigidly mounted.
I also fear the potential for the setup to become "dislocated" in some way. As in, doesnt return to its locating saddles at some point.

For me, the 3-point pivot removed those fears. Regardless of how unfounded they really are

to each his own.

That's why I can't decide which way to go. I want to distribute the weight so I don't create excessive load points but I also don't want the box dancing all over the place.

 

[Schitzangiggles]

For starters, as the chassis twists, the distance between the front pivots and the rear pivot DOES NOT CHANGE.

It stays the same. The chassis is twisting, not deflecting like a leaf spring.

As for the rest of Schitzangiggles post, I dont know what to say.

The setup is a proven setup.

It is simply a "4-point pivot" without the front pivot.

If the chassis did deflect like a leaf spring, the following 4-point that has been used for decades would not work AT ALL.

I'm simply trying to figure it out because I don't know why/how it works. I see deflection in the bushings as providing the majority of the flex vs the front fore/aft pivot points. What doesn't the (for lack of a better term) "reverse dump truck pivot mounts" actually do other than provide a mount point for some bushings?

I'm not trying to flame or bust your chops or anything like that, I'm simply trying to understand the physics involved as I'm noodling a larger rig based on a 5 ton truck so I can take the 8 of us camping off the beaten path and away from all of the Meetards.