So I went down to my ford dealer the other day and cancelled my order for a 2017 F-550 (I’ll have to say by the way the sales guy throw my deposit check across his desk at me I not sure but he may have been just a little upset) after I saw a photo of the new 2017 ford f450/550 cab/ chassis frame or more importantly the frame transition point from box frame section, to C channel frame section, right behind the cab. And yes I know that ford did this to continue to accommodate the aftermarket truck body up fitter companies.

Here is the photo I found on the internet, of the Ford F-450/550 transition design: https://www.google.com/search?q=2017...aR0464zKTxM%3A
All I can say is what a kluged up after thought!!! At first glance basic mechanical design intuition would say the stress loading is not distributed over a large enough area, as evidenced by the addition of doubler plates. However I’m sure the ford engineers have run the transition point through whatever stress analysis programs they may have, many times.

But having said this, one can’t help but speculate which is now truly the strongest frame, the totally boxed F-450 pickup frame design or the half box half C channel f450/f550 cab/chassis.

Did Ford actually end up with a cab/chassis frame that is not as strong as its F-450 pickup sibling?

Over the last 35 plus years of designing aircraft structure there has been more than one time, I found myself or the group I was assigned, backed into a corner, due to cost, evaluability and or schedule concerns, which led to being forced to come up with a quick and dirty design fixes (all of which were NASTRAN proved !!), only to come back later with revisions to redesigned to original concept, this “transition design” reeks of that.

I’m sure that over the next few years Ford will redesign this box to C channel section transition by continuing the outer c-channel section from front to back without a welded joint.

I guess in the meantime I could buy an F-650 and lower the cab closer to the frame by about 8” (don’t know why anybody hasn’t done that yet) and call it an F-555 “Ultimate Duty” (or “Ludicrous Duty”).

What can I say, what I’m I missing here” please explain why I have come to the entirely wrong conclusions, because heaven only knows all the ford dealers I’ve contacted sure hasn’t been any help.

 

A couple of things might be worth considering:

1) Fully boxed frame vs C - channel frame would clearly favor the fully boxed frame assuming that the frame is exactly the same. For example; Freightliner and Peterbilt use C-channel frames for their flat rail (after market frames) and they can carry a lot more than Ford's fully boxed. It comes down to the steel thickness, steel composition and PSI. Until we know some of those details, we are "assuming" that the two frames are of equal composition. I'm not sure we know that.

2) If you need the same wheel base then the F-450 would seem like an easy choice, you can order it with the "box delete". Note that the frames are different. The pickup frame is not "straight". Most outfitters can adjust for this but some don't like the hassle. A "straight" frame is a lot easier to work with.

3) If crew cab is your preferred choice, then the F-450 is again a great choice. Sometimes, vehicles used for work, don't need the crew cab and you can get both the F-450 and F-550 chassis in a super cab or "day" cab.

4) You get one choice of wheel base on the F-450 pickup and a little more flexibility with the F-450/F-550 chassis cab. Something to consider if you're adding a bed/box/utility component to the frame.

Still don't know a lot of details so it's really hard to be making decisions in the dark. GL!

 

I also wondered about the apparently short transition section when I saw that picture but also thought the engineers might have reviewed and thought it adequate. The addition of the second channel "fish plate" indicates some consideration. My thoughts looked more at the boxed frame section which is substantially stiffer than a c channel frame unless this c channel is heavier than those of the past. Stiff frame to flexible frame indicates a point of concentrated flex and distortion at the juncture of the two. You might be correct in turning down this model until better proof is provided. We have all seen older cab and chassis vehicles with the frame failing immediately aft of the cab due to too many trips with too much weight.

 

im a bit concerned about this also, however im more concerned about frame thickness, i would hope that if the frames did indeed have issues ford would make it right! seeing its half fully boxed,im hoping the frame section still utilizes thick guage steel..

 

I don't think there is an issue here, and the reason is that the rear frame is not "hanging," fully stressed on those welded joins. Instead, the great bulk of the weight is transferred through the rear suspension to the rear axle and wheels. I think there is far less stress on that join then you imagine. One thing I do notice is that the c-channel section is considerably taller and thicker than the boxed area on the new pickup configurations at the back.

Ford most certainly has run thousands of software simulations to get the frame right, probably on a program like Solidworks. I'm sure there's been plenty of additional real world testing - we have seen 450 and 550 C/C trucks heavily weighted on the road testing. I believe the only way a C/C frame is going to break at those joins is the result of poor welding - which is probably all done by a computer anyway.

 

I wouldn't worry about that design. My prediction is that this frame is stronger than the f450 pickup frame for vertical loads and similar in strength for all other loads. I suspect there are few, if any stresses that would cause this frame to fail at that joint - and those stresses are beyond anything the frame will see in the real world.

 

I also just noticed the frame joins are asymmetric as well - which will definitely enhance strength at the fail point.

 

I think the worst of this scenario is the salesman throwing your check back at you. A little better investigation and research on his part might have diffused the situation completely and you would still have your truck on order.

 

I would not worry about this. F450 pickups use an F350 frame. Cab and Chassis frames are MUCH stronger. They always have been. Here's a pic of my 94 Super Duty (F450) hauling a 14,700# backhoe. Keep in mind this was a 15,000 GVW truck which weighed 12,000 empty! That's 26,700# on a 15,000 # chassis. Nothing broke or bent. This was in my rookie days, and I would never advise anyone to do this. It's just nice to know that Ford overbuilds their CC frames!

 

Well, we really don't know that for sure do we? The 2015 and 2016 F450 pickups had their own frame that was not shared with the 350 DRW pickup. Maybe they are all the same now but I haven't seen it posted yet. Can someone in the know confirm?

 

The discussion started with the connection of the "C" channel frame to the "Box" frame on the CC models starting in 2017. Previously all trucks were using a continuous "C" channel frame. Now the CC models have a little of each, connected in the middle. On large trucks anytime two frame sections were connected it was done with a "fish plate" which was drilled and bolted in place, never welded (Due to hardening and weakening of the rails due to heat and the loss of flexibility). Ideal was always continuous frame with no connections. Only when stretching the vehicle or repairing damage was the connection ever considered. I also would like to see a little real engineering reported about this connection. And it will take a few years before the "real" time testing proves any of this right or wrong.

 

I was not aware that Ford ever stopped using the F350 frames on the F450 pickups. Do you have a source of this info?

 

The source is Ford itself. From 2011 to 2014 the F450 pickup was identical in every way to the F350 DRW if the 350 DRW was ordered with the high capacity tow package which included the 4.30's and the wide track front end. In 2015 the F450 pickup was redesigned with it's own frame, brakes, suspension, etc. that made it a much heavier duty animal. The S130 rear axle it now comes with is rated to 16k alone.

 

Maybe, but it's really about the weakest link, not the strongest. As for typical frame modification, I would say that robots do weld better than frame shop guys, so you can do more with a robotic weld. Tech does always improve as well. It wasn't all that long ago that "every time you haul a load that large you have to have 6 horses up front" was a fair and valid point.

 

The earlier super duties most cetainly have a welded frame not continuous c channel. In fact, right in front of the shackle on the 99-02, ALL 250-550 truck had a welded boxed section connecting c to box.

Pre 99 had c channel front to back 2wd and boxed front on 4wd for 250-"450."