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 > Frame Stiffing to reduce Porpoising?

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valhalla360

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Posted: 01/23/23 10:22pm Link  |  Quote  |  Print  |  Notify Moderator

mbloof wrote:

Interesting abet comical thread - frame flexing.

If one were to do some Youtube searches you'll likely find videos where trucks from "the big three" are all driven on/over grossly uneven terrain and the frame flexing/twisting (or NOT!) of each OEM was shown and documented.

Generally speaking some OEM's are worse than others and some years are better (and worse!) than others.

- Mark0.


Yes, frames will flex but big difference between a low speed off road once in a while vs repeated 2inch flex for hundreds/thousands of miles cruising down the freeway

Look up fatigue loading failures on google to get an understanding. In a fatigue failure, the item typically looks and operates perfectly fine...until it doesn't. Most of the damage is microscopic and internal to the metal until it finally gives way.


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JimK-NY

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Posted: 01/24/23 05:05am Link  |  Quote  |  Print  |  Notify Moderator

De Nile. It always seems to flow fast and endlessly.

Before considering which shock, which suspension upgrade or in this case welding more metal to the frame, begin with the facts. What is the CCC for your actual truck and what is the actual, measured weight for your rig? When we speculate and use wishful thinking, it seems we think the truck should be able to carry more and the camper weighs less than the actual condition.

JRscooby

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Posted: 01/24/23 05:10am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

mbloof wrote:

Interesting abet comical thread - frame flexing.

If one were to do some Youtube searches you'll likely find videos where trucks from "the big three" are all driven on/over grossly uneven terrain and the frame flexing/twisting (or NOT!) of each OEM was shown and documented.

Generally speaking some OEM's are worse than others and some years are better (and worse!) than others.

- Mark0.


Yes, frames will flex but big difference between a low speed off road once in a while vs repeated 2inch flex for hundreds/thousands of miles cruising down the freeway

Look up fatigue loading failures on google to get an understanding. In a fatigue failure, the item typically looks and operates perfectly fine...until it doesn't. Most of the damage is microscopic and internal to the metal until it finally gives way.


Do you think we should be a little more accurate about how much the frame is actually flexing. How far from the frame is the cabover section of camper? Guess 4 feet or more. 1/8 inch of frame flex would make for 6 inches of movement. And that does not include any flex in the camper itself.

notsobigjoe

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Posted: 01/24/23 06:04am Link  |  Quote  |  Print  |  Notify Moderator

adamis wrote:

Got a question for you seasoned drivers with older rigs. I have a 1999 F350 Dually Quad Cab Long Bed. I've been driving it for thousands of miles and for the most part, it's been fine. However, while driving on rougher roads, I do get a porpoising effect happening. I can look in my rear view mirror and see the frame flexing at least an inch or two.

My camper is the Bigfoot 2500 and with everything loaded up is probably in the 4500lb to 5000lb range. According to the sticker on the camper the center of gravity is almost exactly over the rear wheels. Now the center of gravity does change with water in the tank as the fresh tank is in the front of the camper which puts it at the front of the bed.

The porpoising isn't a "problem" in the since that I am concerned about it causing damage. I'm well within the carrying capacity of the truck. That being said, it is an annoyance for comfort and drivability. I have already replaced the shocks on the truck and that has helped somewhat. I am also looking and seeing that I probably could move the camper another inch or two forward when I load it. I don't think this will make much of a difference though.

So, my next thought was to look at having my frame reinforced. I know there are all sorts of complications when going this route though. Ford does fully boxed frames for a reason because it gives so much more rigidity. I no there is at least one person that has done this on their 7.3 from a posting on the Ford forums. This is obviously a huge expense and extreme measure.

Has anyone else gone through this or found a way to handle excessive porpoising on older C channel frame trucks?


I drilled many holes into my truck frame over the years and was concerned if I changed the original weight rating. I went to a welder shop and the man said it was possible but unlikely given my truck was built in 1996. He said trucks are built differently these days and would have answered yes to my question if I had a late model truck. He filled the holes with welding material and welded a small plate over the spots at my request. I feel no difference what so ever. I hope this helps. My main problem was the front end was too light as the previous owner decide to cut away most of the steel for a custom hood. Again, I feel no differenc.

valhalla360

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Posted: 01/24/23 08:50am Link  |  Quote  |  Print  |  Notify Moderator

JRscooby wrote:


Do you think we should be a little more accurate about how much the frame is actually flexing. How far from the frame is the cabover section of camper? Guess 4 feet or more. 1/8 inch of frame flex would make for 6 inches of movement. And that does not include any flex in the camper itself.


OP appeared to indicate it was when looking at the truck bed when looking in the rear view mirror.

If it's just the cab over movement he's seeing...yeah, it's likely mostly in the camper where the flex is happening and this whole discussion is a big red herring.

HMS Beagle

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Posted: 01/24/23 09:30am Link  |  Quote  |  Print  |  Notify Moderator

adamis wrote:


That contrasts with the 1999 with Max Payload for the Crew Cab Dually Long Bed 2x4 appears to be 5355lbs and the 4x4 is 4910lbs.

https://www.xr793.com/wp-content/uploads/2016/10/1999-Ford-Super-Duty.pdf

So, with basically the same frame, how did they manage to get another 1500+ pounds of payload capacity out of it?


You should go by the Ford bodybuilders manual that I referenced, not by that brochure. The bodybuilders manual gives the specific configurations, in California - less, diesel engine - less. Because the empty truck weighs more. The bodybuilders manual does not give the diesel 4x2 DRW crewcab, but does give the 6.8L, and the diesels are less by about 500 lbs in all models. You could just weigh the empty truck, the GVWR is 11,200 for all models of DRW pickups in those years.

The frame configuration and layout is nearly identical between 1999 and 2015, but the material may be thicker. That is also listed somewhere in the bodybuilders manuals, haven't bothered to look. You probably can't go from 11,200 to 14,000 without doing something.


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Grit dog

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Posted: 01/24/23 10:04am Link  |  Quote  |  Print  |  Notify Moderator

It’s pretty evident the OP is only looking for affirmation from someone (not likely to find that person) who has beefed up their frame for an issue that may not be and likely is not an issue.
The rest of the discussion is, frankly, deaf ears.
But a very important point that maybe scooby just brought up is the amount of movement in the overhead portion that we ALL see from time to time with big TCs is not necessarily indicative of excessive frame flex, nor is porpoising. Unless it’s literally a rocking horse most or all of the time. Which is more likely suspension and shocks. Given the camper weight and configuration changing is not an option.

This has been discussed before. And some folks, who don’t regularly drive big heavy pickups, don’t realize that a good portion of the effect is the vehicle and road configuration.
Anyone who gets porpoising on concrete roads, it likely ain’t the camper as equally spaced contraction joints are still pretty common and they often create a harmonic movement.
Being in the industry, the state of NM about 25 years ago began constructing concrete pavement with randomly spaced contraction joints. I did a stretch of I-40 like that and the result was it wholly eliminated that sensation in vehicles that are susceptible to it.
The reason it happens is cut or cracked edges of concrete swell after they’re cut or cracked. So 1000s of evenly spaced little bumps is what causes that sensation or movement.

* This post was edited 01/24/23 10:18am by Grit dog *


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adamis

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Posted: 01/24/23 10:12am Link  |  Quote  |  Print  |  Notify Moderator

HMS Beagle wrote:

adamis wrote:


That contrasts with the 1999 with Max Payload for the Crew Cab Dually Long Bed 2x4 appears to be 5355lbs and the 4x4 is 4910lbs.

https://www.xr793.com/wp-content/uploads/2016/10/1999-Ford-Super-Duty.pdf

So, with basically the same frame, how did they manage to get another 1500+ pounds of payload capacity out of it?


You should go by the Ford bodybuilders manual that I referenced, not by that brochure. The bodybuilders manual gives the specific configurations, in California - less, diesel engine - less. Because the empty truck weighs more. The bodybuilders manual does not give the diesel 4x2 DRW crewcab, but does give the 6.8L, and the diesels are less by about 500 lbs in all models. You could just weigh the empty truck, the GVWR is 11,200 for all models of DRW pickups in those years.

The frame configuration and layout is nearly identical between 1999 and 2015, but the material may be thicker. That is also listed somewhere in the bodybuilders manuals, haven't bothered to look. You probably can't go from 11,200 to 14,000 without doing something.


Thanks HMS Beagle. I did some research on the frame differences and what I found was Ford did increase the thickness. From this discussion here:

https://www.powerstroke.org/threads/frame-differences.136669/

The frame differences are:

99-04 Crew Cab F-250-350 Pickup 156.2" WB, (6.87 x 2.36 x .240), 6.0
05-10 Crew Cab F-250-350 Pickup 156.2" WB, (6.87 x 2.36 x .264), 6.7

That would explain the payload capacity increase.


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adamis

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Posted: 01/24/23 10:13am Link  |  Quote  |  Print  |  Notify Moderator

Marcela wrote:

I had the same rig for a little while and here's what I found out.

The bed opening width is minimal. The curved part at the bottom necessitated that I use two pieces of plywood to raise it above the curvature.

Make sure your bed is flat. On my new GMC truck the bed is crowned front to back, which necessitated different pieces of plywood of varying thickness.

Re the center of gravity. I had race car scales so I put my camper on them. If you look at some of my old posts you can find out what I found out. There guesstimate is best case, what I found out was different. Though the cog was behind the wheels a bit, I didn't find it to effect the driving.

Also on my F250 I had the biggest spring pack installed and largest sway bar. I still didn't like the way it drove. The cog is just so high.

I removed and reinstalled my jacks on the camper. When they installed them the holes in the brackets were too small for the fasteners used there is no way they would pull up tight against the camper. So I enlarged the holes in the brackets and reinstalled.

Also if you have a gooseneck ball in the bed, you can install the plywood on the bed with a hole that matches this and install a stub into and flush with the plywood to hold it in place, or two pieces if that is what you do.

Good luck.


Thanks Marcela, I like your idea on using the goosneck ball mount to help hold things in place. That is a great idea and something I will definitely look into for a future project.

adamis

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Posted: 01/24/23 05:40pm Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

But a very important point that maybe scooby just brought up is the amount of movement in the overhead portion that we ALL see from time to time with big TCs is not necessarily indicative of excessive frame flex, nor is porpoising. Unless it’s literally a rocking horse most or all of the time. Which is more likely suspension and shocks. Given the camper weight and configuration changing is not an option.


Perhaps my use of the word porpoising was just the wrong terminology and that set you off. What you are describing is what I am observing. The camper overhead rocking slightly up and down on rough roads. When that happens, I can look in the side view mirror and what I observe is these lines flexing ever so slightly.

[image]

Now, I don't have a way to measure it, I guesstimated 1 to 2" but probably more likely in the less than 1" range now that I think about it again. So, everyone else, while you are driving down the road and come across a bumpy section and see the overhead portion moving up and down, take a look in your side view mirror down this sight line and I am betting you will observe some movement as well.

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