Lots of frame flex.
#1
05-13-2010, 09:02 PM
Lots of frame flex.
I got my 4x4 F250 cross axled in a ditch leading into a cattle pond with about 2,000 on the flat bed. It was bad enough that both the LR and RF got light and took turns lifting, so I got out to take a pic of it. That failed becuase it was almost dark and I was using my phone, but I noticed that the frame flex alot. I mean it had a real twist to it!
It went right back as soon as I got it heading straight up the side rather than across, but how much is normal?
It went right back as soon as I got it heading straight up the side rather than across, but how much is normal?
#2
05-13-2010, 11:01 PM
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#5
05-14-2010, 12:34 AM
<img src="http://www.bigblocksix.com/f100swb/f250/wheeling/sioux%20mountain/posinattop2.jpg" width="600">
Not my picture but I see about that much flex on a somewhat regular basis.
#6
05-14-2010, 12:53 AM
#7
05-14-2010, 01:11 AM
The era of ford trucks up to 1996 were designed with the mentality of old school engineering that perhaps goes almost as far back as the model T. The frame simply put, was considered to be part of the suspension of the truck and designed to flex and float as the vehicle covered obstacles under load. The idea was to allow good ground contact without having to lift the truck higher up on longer travel suspension (back in the 70s, LOWER was considered better for pickups, now higher is cool). This, combined with the twin I beam suspension allows these trucks to have unmatched ground contact on uneven terrain even with open differentials. The only other way you could get that type of result was with some form of soft, long travel suspension on a heavy, rigid boxed frame.
The open channel rails are extremely flexible and can twist back and fourth repeatedly without being damaged or cracking from metal fatigue (within reason!). This also allows the frame to better survive shock impact from say, hitting a ditch if its deeper than suspension travel.
If you guys remember the marketing for when the 2004 F150 was first introduced, they claimed a 9x stiffer frame. That was a reference to the torsional stiffness of the truck and marked a complete reversal of the previous design philosophy. Ford did this with a fully boxed frame. This makes the truck stiffer on roads and handles much better, but also makes it fairly heavy and increases the over all height of the vehicle without any gain in interior space or ground clearance compared to older trucks. Although judging by sales, it seemed to be the right call.
Personally I like the flexy frames because they have a good track record for delivering well over 20 years of reliable service life in many different models of fords over the decades that the F-series was in production. They also drain better for those of us that might allow our trucks to see mud, salt or rain on occasion. The closed boxed frames have been used on imported trucks for a long time and thats one reason why they rust out so badly (thinner steel improves the strength to weight ratio, but also makes it more vulnerable to rust).
The open channel rails are extremely flexible and can twist back and fourth repeatedly without being damaged or cracking from metal fatigue (within reason!). This also allows the frame to better survive shock impact from say, hitting a ditch if its deeper than suspension travel.
If you guys remember the marketing for when the 2004 F150 was first introduced, they claimed a 9x stiffer frame. That was a reference to the torsional stiffness of the truck and marked a complete reversal of the previous design philosophy. Ford did this with a fully boxed frame. This makes the truck stiffer on roads and handles much better, but also makes it fairly heavy and increases the over all height of the vehicle without any gain in interior space or ground clearance compared to older trucks. Although judging by sales, it seemed to be the right call.
Personally I like the flexy frames because they have a good track record for delivering well over 20 years of reliable service life in many different models of fords over the decades that the F-series was in production. They also drain better for those of us that might allow our trucks to see mud, salt or rain on occasion. The closed boxed frames have been used on imported trucks for a long time and thats one reason why they rust out so badly (thinner steel improves the strength to weight ratio, but also makes it more vulnerable to rust).
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#8
05-14-2010, 01:28 AM
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good explanation, my 94 f350 on 38's has been flexed to near breath taking sights before. it is somewhat surprising to see how much differential there can be between the cab and box. even more so with my 85 f150 on 36's. that one's frame broke, but it was at the steering box and had nothing to do with frame flex. i haven't driven offroad in a box frame truck, but completely agree and understand what you are saying
#10
05-14-2010, 01:44 AM
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#11
05-14-2010, 02:05 AM
I should also add another reason why the cabs on our specific era of trucks from 1980-1996 flex apart from the box so easily (Earlier years may also apply but not sure). The forward cab mounts are far apart and mounted outboard of the frame rails providing a wide, solid base. This is where most of the weight of the cab is and this also gives a stable mount to attach the rear of the fenders to. Also note, the flexible upper rear fender mount.....
The rear mounts however are located inboard of the frame rails on a cross member. This almost simulates a tripod mounting setup and allows the cab to more or less follow the the stiffer forward mounts while the rear mounts have a narrow enough base to allow the cab to "pull away" slightly from the frame without excessive stress. The box on the other hand is hard mounted, so it follows the frame twist directly where its attached.
My Dad's 1993 GMC for example has all outboard cab mounts and gives the appearance of a much less flexible truck because the box is tied much more rigidly to the cab through the frame......in reality, his truck has a frame that simply forces the cab to follow. It looks better at a first glance but his newer truck creaks and groans much more than mine when twisted and his doors have a harder time lining up (the longer doors don't help either though).
The rear mounts however are located inboard of the frame rails on a cross member. This almost simulates a tripod mounting setup and allows the cab to more or less follow the the stiffer forward mounts while the rear mounts have a narrow enough base to allow the cab to "pull away" slightly from the frame without excessive stress. The box on the other hand is hard mounted, so it follows the frame twist directly where its attached.
My Dad's 1993 GMC for example has all outboard cab mounts and gives the appearance of a much less flexible truck because the box is tied much more rigidly to the cab through the frame......in reality, his truck has a frame that simply forces the cab to follow. It looks better at a first glance but his newer truck creaks and groans much more than mine when twisted and his doors have a harder time lining up (the longer doors don't help either though).
#13
05-14-2010, 02:15 AM
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i hate all the wide screen b/s nowadays too. my 19'' is over 7 years old. it's my parents old monitor. i wish i had the 22'' widescreen they have now, because it does get old to scroll side to side, but i wouldn't ask someone to resize an image for my comfort. that is just too needy for my taste
#15
05-14-2010, 02:43 AM
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