94 F350 four door dually 2wd 7.3 idi
When I carry my Lance truck camper I notice a lot of flex between the bed and cab. Also when empty I notice this. It seems like the flexing is so bad that when I run over a pothole in the road the body flexes instead of allowing the suspention to work, this making the ride quality worse.

Is there some way to stiffen the frame?

Would it cause some other problem if the frame had some kind of homemade stiffener added?

 

My frame does the exact same thing..It really does it bad when i go off road...My dad has a 1994 idi crew cab 4x4 long box and his is even worse..I just think its because its so long..

 

$64000 question. If you eliminate this flex, which is pretty much common to all makes/models of this type of truck, where is the next point that will flex? You risk concentrating stress and creating a failure point.

Despite the many failings of manufacturers, they do stress test their frames.

Check the threads here. Do you see any "My frame broke"?

 

I'll bite... My frame broke. '83 F-150 stepside 4x4. Snapped it dang near in half, and blew a rear shock mount clean off the frame!

Near as I can figure it happened during this one time I was playing in the mud... I didn't notice teh frame cracked in half or the missing shock mount until after the truck burned down, so it's hard to pinpoint the time of failure or if the frame and shock mount failed at the same time.

So I bonzai'd a mud hole at a good clip, no seat belt, didn't have wipers on. Once hitting the hole, of course the truck wanted to slow down, I stayed on the gas, pedal to the metal. Fumbling for teh wiper switch to clear all the mud off the windshield I finally got it on, just in time to see I had veered off course and was about to hit a tall hill at speed. No time to do anything except brace myself. Not well enough though! After a brief stint in the air (my buddy swears I was 5-6 feet off the ground, I believe it from the hill and the impact) I graced Gods fine earth with my presence again.

Upon this glorious return I was shoved across the bench with my foot somehow jammed to the floor on the gas. Futility be damned, I tried to get back behind the wheel, catching occasional glances of trees whizzing past on each side as I roared over many whoops, truck bouncing wildy in the air. After giving up on freeing my foot from the loud pedal, I yanked on the shifter *** hard as I could and eventually got the bugger into neutral, slowed the truck, and freed my leg.

It was fun as heck, but I was quite sore. The end result was the frame rails were both completely separated on the bottom and sides, and on one side the top of the C channel was just hanging on by a thread. Also the drivers side shock mount was blown clean off the frame, dutifully still attached to the top of the shock, just along for the ride.

Yeah, that was a good truck. Lots of fun times in that thing. I got stuck far too many times from the frame flexing though. It's very bad when you're going up steep hills and need to downshift but when the clutch is to the floor it's not disengaged... Due to the frame flexing the z-bar couldn't pivot enough to release the clutch. Newer trucks with hydraulic setups don't have this problem. It's all just as well though, as the truck must have decided it didn't like me any more, and burst into flames in my driveway about a week later.

Anyhow, I now carry a fire extinguisher in my F-250, and will be boxing the frame eventually.

 

Simply WOW! Sounds like something I would do. By any chance you didnt say "hey y'all watch isss!!" prior to these actions did you?

 

Ladder frames (as your pickup has) are notoriously "twisty" because there's no triangulation whatsoever. Because they're thick and meaty, they resist bending loads (i.e. the load in the bed pushing down) very well, and that's the primary purpose of a truck frame anyway.

The cab and bed provide some minor triangulation which resists twisting forces, but since the bed and the cab are not attached to one another the frame underneath can twist at will.

Add to that worn out cab/bed mounts, worn crossmember rivets down the length of the frame (front to back), and the flexing just gets worse over time. It's inevitable.

You can weld the crossmembers to the frame or replace the loose rivets with graded bolts and tighten/replace the cab/bed mounts but there always be some twistyness due to the design.

The only way to get rid of it is to triangulate the frame - and that's probably more work than its worth.

 

A beater F-250 I had for a while... Observe the frame flex. Never broke that frame or shock mounts and I beat that truck harder than the 150 that cracked in half.

http://s121.photobucket.com/albums/o234/cadunkle/?action=view&current=MVI_0343_converted.flv