Dropping a C30 flatbed

[SCOTI]

Originally Posted by Mike Bradbury

Do the brackets that bolt to the axle for the 4 bars have the perch for the bags? Still trying figure out how you mounted the bags behind the axle with out welding brackets to the tubes.

I am going to do a complete cab back custom frame so if I need to tweak anything I can in the design phase. The bags look close to the wheels in your pics, Do you find any clearance issues when the axle is twisting left and right over uneven road surfaces?

Yes, the lowers have the bag brackets as part of the lower plate. They are designed so that it positions the bag under the frame rail for mounting.

The problem w/that was the truck would have been close to stock height @ the recommended bag inflation/installed height. I solved that by swapping the two sides so that the bags were kicked just outboard of the frame (basically in-line where the leaf was). This allowed me to make my top mount where I needed it for the truck to be @ the dropped ride height I wanted w/the bags @ their recommended inflated/installed height. It's worked well but kills the 4x cut-down semi wheels for the rear (you'd have to run a stock steel inner on my set-up).

You could do similar but different. Where I have the bags mounted to the leaf-spring adapter plates, you would need to have a 'bridge-bar' attached. That ties the two sides together & allows moving your bags/mounts to just inside the frame just like they would be if mounted off the rear housing (but w/o welding to the tubes). The downside is it gets crowded real fast between the rails & you have to put the Panhard bar above the center housing.

If I were doing a HD 6x-72??

I would utilize a 3/4 ton T/A set-up. I have dibs on a 68 3/4 ton truck a former retired co-worker has & it's just for this purpose. Putting the bags in the stock position yields 5-6" of drop. If more drop @ ride height is desired, a 'bridge -bar' bar that anchors to the original spring mounts can be utilized & new top mounts built off of the frame rail as needed to achieve the desired height wanted w/the bags @ their recommended inflated/installed heights.

[Mike Bradbury]

Well like you I prefer the support of the truck on the outside of the frame for stability, and like I had said, I am doing a complete cab back new frame. I like the stability of the 8" frame rails and I am not going to get too outside the "box" (pun intended) with a bunch of tubes going every which way. I feel the simpler the better but also stronger. I will be using 8" rectangular tubing that is gradually reducing in width. But also I will be able to "squeeze" the frame width in order to accommodate outside the frame mounts of the air bags. I am talking only about an inch on each side over the 8' length so it will hardly be noticeable.

[SCOTI]

Originally Posted by Mike Bradbury

Well like you I prefer the support of the truck on the outside of the frame for stability, and like I had said, I am doing a complete cab back new frame. I like the stability of the 8" frame rails and I am not going to get too outside the "box" (pun intended) with a bunch of tubes going every which way. I feel the simpler the better but also stronger. I will be using 8" rectangular tubing that is gradually reducing in width. But also I will be able to "squeeze" the frame width in order to accommodate outside the frame mounts of the air bags. I am talking only about an inch on each side over the 8' length so it will hardly be noticeable.

Gotcha. Barnes 4wd makes some nice HD leaf spring style plates: https://www.barnes4wd.com/

They would be a good starting point. These are lighter duty 1/2 stuff but you basically want to make a HD version of these...

[Mike Bradbury]

Great, that is exactly what I was needing. I will be building the entire suspension but I just needed an engineering starting point.

I am going to be rebuilding the rear axle like on my C10, so I may remove the top brackets and weld the brackets on the bottom of the axle so the four bars find more secure anchoring. This may require straightening the axle but I may isolate the heat affected zone similar to how you did.

[SCOTI]

Originally Posted by Mike Bradbury

Great, that is exactly what I was needing. I will be building the entire suspension but I just needed an engineering starting point.

I am going to be rebuilding the rear axle like on my C10, so I may remove the top brackets and weld the brackets on the bottom of the axle so the four bars find more secure anchoring. This may require straightening the axle but I may isolate the heat affected zone similar to how you did.

Barnes 4wd for the HD leaf plates. Tinworks Fab prob has the HD flip brackets available as individual pieces. Barnes might have a leaf perch as well.
Only tweak I would aggressively recommend is this for anchoring the bag mounting plates to get more contact area under the lower rear-end plate:

[D-n-Tyke]

Originally Posted by Mike Bradbury

Great, that is exactly what I was needing. I will be building the entire suspension but I just needed an engineering starting point.

I am going to be rebuilding the rear axle like on my C10, so I may remove the top brackets and weld the brackets on the bottom of the axle so the four bars find more secure anchoring. This may require straightening the axle but I may isolate the heat affected zone similar to how you did.

I am sure you already have access but if you need any help with engineering/solidworks work coming up with your design let me know.

[Mike Bradbury]

Are you a solid works guy? That is good to know. The weld school I teach at has a CNC plasma cutter but the Torch mate program is so annoyingly proprietary it is difficult to work with. Most of the brackets I can cut without much trouble, but it is generating the animation of the rear suspension articulation and the custom flat bed details will be extremely helpful.

[D-n-Tyke]

Originally Posted by Mike Bradbury

Are you a solid works guy? That is good to know. The weld school I teach at has a CNC plasma cutter but the Torch mate program is so annoyingly proprietary it is difficult to work with. Most of the brackets I can cut without much trouble, but it is generating the animation of the rear suspension articulation and the custom flat bed details will be extremely helpful.

Yes sir . Work with it daily.

[Mike Bradbury]

For a school project a couple years back we used our CNC to cut out 68 plates that when assembled made a bust of MLK. It is now on one of San Diego's city streets as a memorial. It was a fun build to see it come together.

[SCOTI]

That's freakin' awesome!

[Mike Bradbury]

Yeah it really stretched my students and it was quite a process.

[rodstored-72]

mike, that is REALLY cool! I like the thought behind it. At first glance it looked like a 3d print in plastic..... nice job!

[Mike Bradbury]

No plastic, it was designed to be outside and withstand the weather and elements. It is actually .250" stainless steel. it weighs 750 pounds! and we needed a fork lift to get it in place. We applied an acid based patina to get the bronze look.