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Is the bed supposed to look like it's flexing a lot going down rough road?

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Detroit80, Sep 18, 2020.

  1. Detroit80

    Detroit80 Full Access Member

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    Truck is a '90 CCLB 4x4, bed has been replaced with a flatbed before I got the truck. Bed was definitely not done "right" with spring loaded clamps on the frame that I see on modern commercially installed flatbeds, and instead just u-bolted to the frame with some steel tube and plate spacers to accommodate the over axle rise, in a very backyard redneck engineered way, lol.

    I live out in a rural area on dirt roads, with the usual bumps, dips, holes, etc of "out there" roads. Driving down the road, looking through the windshield mirror, I can see the headache rack moving back and forth what looks like 5-6 inches in both directions. It's a smooth movement, not jerking around like it's loose on the frame. Headache rack is welded to the flatbed too, so it's not moving on it's own. I have a headache rack bolted to the pickup box on my '96 Chevy K2500 too, and have never seen it moving around like this on the same roads, but the Chevy obviously isn't built anything like the Ford is either, lol.

    I know long wheelbase trucks will have some frame flex, and you don't want extreme rigidity in the frame, but I'm not sure how much is too much, or if this is normal with having the flatbed directly clamped to the frame? I ask because this truck has been parked for about 9 months now, and now my other daily truck is having major issues, so I'm considering selling that one and putting the Ford back on the road. But I don't want to dump a ton of time and money into this truck only to find out I have major frame issues or something else like that afterwards, lol. I don't recall ever having felt/seen other indicators of a broken frame, and have had 10K+ pounds on the trailer hitch many times.

    I'm planning on pulling the flatbed off soon to do some work on the fuel tanks, due to a tire blowout taking out the fuel filler on the rear tank, and some other issues back there too, so I will have a chance to take a better look at the frame overall.
     
  2. gandalf

    gandalf Senior Member

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    I discovered, on my first truck, an '86 extended cab, that these Fords have a surprising amount of flex. I learned about this driving down a dirt road (I'm being generous with the term) with my cabover camper. I ripped the tiedown eyebold out of the camper when the truck flexed and the camper was unable. I later was told that the bed, unloaded, could flex 7-8 inches, corner to corner.

    My trouble came when I put a non-flexing camper into a flexing truck bed. I suspect you're running into much the same problem. Your flatbed is not able to flex as much as the truck frame.
     
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  3. u2slow

    u2slow bilge rat

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    I remember the flex being considerable on my F350 crew pickup. No doubt if you double the bed height with a headache rack, the same twist is going to look twice as bad.

    Try a 3-point mount (fwd mounts rigid; rear mount pivots) or spring load the aft 2 mounts for some give.

    This old pirate4x4 thread has some discussion, but the pics are dead
    https://www.pirate4x4.com/threads/suggestions-for-flexy-flatbed.1074920/

    The 88+ Chevy has a significantly different frame and suspension. IMO, the Ford frame was engineered to flex quite a bit more... more like an 87-older Chevy and 93-older dodge.
     
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  4. Detroit80

    Detroit80 Full Access Member

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    I probably over explained with too much detail again...I have a tendency to do that, lol.

    It's not so much that I consider it a problem or that it bothered me, but rather that I didn't know if it was a sign of some other major issue, such as a cracked/broken frame, and didn't want to toss a couple grand into rehabbing the truck only to find that I should have been looking for a replacement truck altogether.

    Perhaps somewhat ironically, I also use this truck for a camper - a massive Lance LC980, though I always tied it down straight to the flatbed rather than the frame for that exact reason - fear of ripping tiedowns out of the camper.

    But it sounds like this is pretty normal, at least given the way the flatbed is currently mounted. Regardless, I was planning on redoing the mounts altogether, so that it's more securely mounted via bolted mounts, basically set up the same way that 6x6 is from the Pirate thread - two solids in the rear/middle, and spring loaded up front.

    But I do feel a heck of a lot more comfortable moving forward with this truck now...I sure do miss the pulling power of that 7.3 vs the 6.5 in the Chevy.
     
  5. WAID

    WAID Full Access Member

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    I more or less assume Ford was a little confused on the concept of suspension articulation and just built more of it into the frame than the suspension.
     
  6. riphip

    riphip Supporting Member Supporting Member

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    My '86 X-Cab does the same & makes stress cracks in the bed corners
     
  7. Scotty4

    Scotty4 Supporting Member Supporting Member

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    Just backing into my parents driveway it causes enough sway to make the bed topper look as if it is going to fly off... lots of flex to these frames.
     
  8. gandalf

    gandalf Senior Member

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    My '86 has stress cracks also, back near the tailgate as I recall.
     
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  9. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    After working on both of these for over 6 years, this doesn't surprise me one bit. The 6.5's are better (not great) with an automatic. The 5 speed that was put behind them had gear ratios that were WAY too widely spaced. They would drop 1500 RPM between shifts which dropped the engine completely out of the boost range.
     
  10. Detroit80

    Detroit80 Full Access Member

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    Mine does have an automatic...and a 5K trailer load damn near brings it to it's knees. I couldn't even begin to imagine loading my camper on it AND pulling the crawler on the trailer, which the Ford does without issue. Sure, I'm in the right lane with the semis doing 10mph on steep grades, but it's pulling the hill...

    That said, the Chevy does make for a MUCH more comfortable long distance cruiser, but if I were to do it over again, I definitely would have either held out for a 454 truck, or put one in this truck from the get go. Though even then, I'm not sure I'd trust the truck to hold up to 4K in the bed and 6K on the hitch....I just don't think the frame and suspension was built stout enough to do that.
     
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  11. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    5k is a different story. That's brave in my opinion.
     
  12. Detroit80

    Detroit80 Full Access Member

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    I really didn't think 5,000lbs was asking too much of a truck sold as a heavy duty 3/4 ton....(mine is the 8 lug with 14b full floater rear)

    Obviously I was a bit faulty in that assumption. cookooI mean hell, my Jeep Grand Cherokee with a damn unibody and small gas V8 had less issues pulling 5K than this truck does...but then I've seen the same thing over in the Chevy specific forum boards too..." Damn...6,000 pounds on the hitch? That's ballsy!"
     
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  13. david85

    david85 Full Access Member

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    These trucks are designed to flex because the frame was considered part of the suspension. It was a cheap way of giving good contact with uneven road surfaces, without having to engineer a complex, long travel suspension. This saved weight, cost and lowered the overall height of the vehicle. Just look at how high you have to step to get into a modern pickup compared to an older one. These days everyone has gone to fully boxed frames and near 100% rigidity. Lower overall profile is now seen as a negative, so the bigger, the better. Technology changes and people's preference also change as time goes on. But wow, does it come at a cost! (new trucks are insane!)

    If you look at the cab mounts for the 1980-1997 fords, you'll notice the front mounts are outboard of the fame rails, while the rear mounts are inboard. Narrowing the rear allows the cab a little more leeway to move independent of the frame, almost like creating a tripod footprint. The box beds are very flexible, because they are rigidly bolted to the frame have to be able to follow it. This can wreak havoc on canopies or headache racks at the rear corners where cracks can develop.

    Floor cracks and firewall at the front cab mounts are common on bush trucks, but I have yet to see the cracking described at the rear of the box. I don' doubt that it can happen though.

    I've sometimes toyed with the idea of adding some cross members to try and increase the torsional stiffness. Maybe even box some portions of the C-channel to mimic a modern frame...but then I remember my truck is over 30 years old and still doesn't have any frame cracks anywhere. Being a 2wd pavement queen probably didn't hurt.
     
  14. Detroit80

    Detroit80 Full Access Member

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    I feel like it's been the exact opposite for me. This F-350 feels like the tallest factory height truck I've ever had, with my '96 Chevy K2500 4x4 being WAY lower, along with the '05 Ram I had prior though it was a 2WD, and the current '10 Ram 2500 4X4 I use for my work truck.

    But then I look at other 1990 F-350s online, and they all seem like they're sitting lower than mine. I feel like mine has a lift kit in it, but I already have negative arch in my front springs, and I can't see any possible way that the front could be sitting lower than it is now. Yet, there's still gobs of empty space in the front fenders, and looks like I'm running a much too small tire on it...

    It has 235/85R16 tires on it now, and yes, its DRW wheels on the front and SRW on the back...I have DRW axles front and rear under it, but had a couple blowouts last year, and ran out of good DRW spares..so I put a couple SRW wheels on the back temporarily. Front tires turned a bit to the left, axle isn't pushed pack :p

    IMG_20200918_193022.jpg
     
  15. david85

    david85 Full Access Member

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    Well, you can't really compare a solid front axle to anything with independent front suspension. Even twin I-beam allows for a lower stock ride height than your D60. My Dad's 1993 4x4 K3500 diesel had A-arm suspension and it was also relatively low to the ground for the same reason. But A-arm suspension is much more complex and requires a boxed frame to support it. All of that made it more modern but also more expensive to produce. The one advantage of the old ford design was the frame rail is one piece bumper to bumper even on long F350s like yours. Boxed frame trucks rely on sections welded together, which are typically made of thinner steel to save weight and cost. This gives them more torsional rigidity for a modest increase in weight, but the disadvantage is they are very vulnerable to rust over the long term.
     

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