towing with my lowered crew cab

[Frank Enstein]

I'm looking into this myself for Frank (my dually) I also plan to use a 4 link and air bags. I will buy a c notch kit and add boxing plates to the frame. My thoughts on the boxing plates are to not weld continuous but to weld an inch and skip an inch. I also plan to make the boxing plates have a "C" on each end so the load doesn't stop all in one spot but tapers off to prevent stress cracks.
I weld O.K. bit I always try to build everything so the weld just reminds it not to fall apart rather than needing the strength of the weld for support.

I don't mean to hijack the thread but opinions on my plan may give valuable insight into the OP's project.

 

[618 Syndicate]

I'm looking into this myself for Frank (my dually) I also plan to use a 4 link and air bags. I will buy a c notch kit and add boxing plates to the frame. My thoughts on the boxing plates are to not weld continuous but to weld an inch and skip an inch. I also plan to make the boxing plates have a "C" on each end so the load doesn't stop all in one spot but tapers off to prevent stress cracks.
I weld O.K. bit I always try to build everything so the weld just reminds it not to fall apart rather than needing the strength of the weld for support.

I don't mean to hijack the thread but opinions on my plan may give valuable insight into the OP's project.

I'm redoing the notch on my 2 linked dually, cutting it down and adding a bridge, moving the bags to the axle. It's done poorly now, set up for maximum lift with the bags way in front of the rear wheels. The rear will go from laying frame to looking like it's lifted. Completely useless for towing.
Do your research on bag location if you want to be able to tow.

 

[Frank Enstein]

My plan is to make a bridge and mount the bag on top of the axle. My goals are easier load/unloading (bags flat) and improved ride when empty with more travel. I want to lower it 2 maybe 4 inches but no more. I may not even need a notch. My shocks have 10 inches of travel but the leaf springs have maybe 5 so it rides kinda rough on choppy roads when empty. Put 500 pounds in it and it's fine.

 

[618 Syndicate]

If all you're doing is dropping it a max of 4, use helpers. Easier and cheaper.

 

[Frank Enstein]

I will try 2" drop shackles and see if I like the height. The air is for ride quality, kneeling for loading/unloading, and the ability to not hunt squirrels at night when I'm loaded.

I fear I've completely threadjacked this thread.

We now return you to your regularly scheduled OP's thread.

 

[618 Syndicate]

I will try 2" drop shackles and see if I like the height. The air is for ride quality, kneeling for loading/unloading, and the ability to not hunt squirrels at night when I'm loaded.

I fear I've completely threadjacked this thread.

We now return you to your regularly scheduled OP's thread.

Bags aren't going to get it lower than the springs will allow.

This thread was all but dead already...

 

[stutaeng]

Just for a little more info: with the way the stresses are generally applied to the truck's frame with a bumper pull trailer, the strength of the frame is proportional to the cross section. So, if you are cutting out 1/2 the height of the frame and doubling the thickness with the brace, you are breaking even. If you remove more than 1/2 the height, you will need to increase the thickness by a proportionate amount.
Also, if you are not a competent welder or do not have the right equipment, you are better off just bolting the brace to the frame. The shear force a 1/2" grade 5 bolt can withstand is 10,000 lbs. A grade 8 is 30% higher. So having 6 to 8 bolts through the frame and brace will more than handle the stresses applied. As mentioned above, the Heat Affected Zone around the weld is the weakest area. An improper weld can reduce the strength by far more than removing material did, just due to changing the properties of the metal.
Therefore, I believe most c-notch kits on the market are designed well enough to support the max tow ratings of the truck.

Sorry, did not not look at the threads since my last post. But this is incorrect.

The section modulus is of the mathematical term X to the power 3!

Ix = bh^3/12



So for any dimension you lose in depth, you better have a factor of 8 in area to equal the same moment of inertia..


I will post a basic hand calc. tomorrow if I remember myself!

 

[drewcrew]

Sorry, did not not look at the threads since my last post. But this is incorrect.

The section modulus is of the mathematical term X to the power 3!

Ix = bh^3/12



So for any dimension you lose in depth, you better have a factor of 8 in area to equal the same moment of inertia..


I will post a basic hand calc. tomorrow if I remember myself!

WAY over my head.

 

[Supercharged111]

WAY over my head.

Basically, which I suspected, what he's saying is that frame height increases strength FAR more than material thickness.

 

[stutaeng]

So if you consider steel section .125" wide x 8" high and bending about the neutral axis and you need to reduce the depth to 4":

Case 1: The moment of inertia is 5.33 in^4. Area is 1.0 in^2

Case 2. Reducing the depth to half: .125" x 4" high. The moment of inertia is 0.67 in^4. About 1/8 of the one is Case 1.

Case 3. Reducing the depth half, but adding twice the thickness: .25" x 4" high. The same area Case 1 (1.0 in^2.) The moment of inertia is only 1.33 in^4.

To maintain the same moment of inertia of 5.33 in^4 in Case 1, the section needs to be 4" high by 2" wide. A solid 2x4 of steel! LOL

I forgot what this thread was about!

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