Gusset or Go Fish- Frame Question

[divemaster5734]

This C350 project axle swap opened up a nasty can of worms.
It's exacerbated by my general ignorance of most things suspension, but I'm learning.
I'd heard rumors they shortened the F350 frame to fit the Bronco cab, but I was told by Sky Offroad this would be a simple direct bolt on.
That's not quite true.
They cut the frame at the forward rear spring hanger.

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As you can see, they welded the frame back together center of the hanger, then added a fish plate on the inside.
The small arrow points to the back front hanger rivets, the big arrow points to the three holes they drilled for the front of the hanger.
I started to ream the front holes to mount the back new rs hanger mount, then became worried about loosing structural integrity of the frame.
You can see the marks from the fender washers where they remounted the hanger.
I know know that those holes were dangerous, and probably held only because of the body support. That said, all the bushings were completely wasted.
I'll need to widen those forward holes a bit more to fit the hanger.
I'm wondering if after I route those holes enough, a clean, undrilled fish welded in place, then drilled to exact size and location would provide adequate support, or should I set another gusset next to the existing?
Below is the outside of that frame with the hanger close to position.

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You can see how far off the two rear holes are.
Which brings up another question.
I'm not going to be able to mount the hangers level, as the frame bends down.

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You can see the vertical frame weld.
If anyone has a 87-90 F350 could you let me know if the front spring hanger is on level frame?
I need to determine the mount angle.
The instructions say to install a spacer on the bottom of the forward hanger, using a pre-drilled hole.

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Following C that makes the hanger sit at an angle.
I can mock up the mount on a table vise and copy the intended angle with a digital inclinometer.
My other option to a gusset or fish would be to weld the existing rear mount holes closed, grind, sand, and redrill.
I've never done a major suspension mod, only bolt on kits for normal freaking trucks.
Any insights greatly appreciated.
Thanks

 

[FrozenMerc]

First, the hole size is not that critical. The hole does not support the bolt and bracket in bearing on the OD of the bolt, the clamp load generated by the proper torquing of the bolt and the friction between the mating surfaces provides the support, so your holes can be a bit oversized, the bolt will never touch a wall, and it won't effect anything. In fact, the factory holes were probably considerably oversized (+ 0.060" or more) to account for manufacturing tolerances in both position and size.

That said, those holes are buggered enough that I think your best bet is to weld them closed, grind smooth, and redrill.

I say this as the former Validation Engineer for Reyco-Granning Suspensions. I have done a number of suspension swaps on much heavier trucks than your F350 with good success. The image below is probably the knarliest suspension swap I ever did. It was an air ride conversion on an 86,000 lb Rosenbauer Ladder Truck. The drive axle was rated at 35,000 lbs alone, and everything had to be modified to get it to fit. Fuel tank, cross-member, air tanks, running boards, etc.

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[u2slow]

I might burn on a chunk of flatbar as a backing with the 'right' holes.

I dont feel level matters so long you are wise to the fact that the 3 eye-bolt positions change the height and spring attitude slightly.

I have seen SKY's brackets before and they are beefy. Probably splice a frame with those alone.

 

[u2slow]

In fact, the factory holes were probably considerably oversized (+ 0.060" or more) to account for manufacturing tolerances in both position and size.

The factory mashes a hot rivet into each hole to take up any slack.

 

[divemaster5734]

First, the hole size is not that critical. The hole does not support the bolt and bracket in bearing on the OD of the bolt, the clamp load generated by the proper torquing of the bolt and the friction between the mating surfaces provides the support, so your holes can be a bit oversized, the bolt will never touch a wall, and it won't effect anything. In fact, the factory holes were probably considerably oversized (+ 0.060" or more) to account for manufacturing tolerances in both position and size.

That said, those holes are buggered enough that I think your best bet is to weld them closed, grind smooth, and redrill.

I say this as the former Validation Engineer for Reyco-Granning Suspensions. I have done a number of suspension swaps on much heavier trucks than your F350 with good success. The image below is probably the knarliest suspension swap I ever did. It was an air ride conversion on an 86,000 lb Rosenbauer Ladder Truck. The drive axle was rated at 35,000 lbs alone, and everything had to be modified to get it to fit. Fuel tank, cross-member, air tanks, running boards, etc.

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Appreciate the input.
I knew the hangers were a tension vs sheer mount, but was more worried about the frame integrity.
That's some nice looking work.

 

[franklin2]

Welding guys in the know always told me do not weld a fishplate on all 4 sides. If on a frame, only top and bottom, no vertical welds. Something about closing it in on 4 sides causes a bunch of stress when it cools and it will have a tendency to crack later on at the welds.

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[FrozenMerc]

Vertical welds on members that are primarily in bending (frames, axle tubes, etc) are always a bad idea from a fatigue life standpoint. The bending stress is near zero at the bending axis / centerline, but grows as the weld travels away from the centerline. This causes fatigue cracks to start at the ends of the weld and grow rapidly along the weld. A horizontal weld, or one that is parallel to the bending axis has a more uniform stress gradient, so when a fatigue crack starts, it doesn't grow nearly as rapidly, especially if the weld is close to the centerline.

 

[divemaster5734]

Welding guys in the know always told me do not weld a fishplate on all 4 sides. If on a frame, only top and bottom, no vertical welds. Something about closing it in on 4 sides causes a bunch of stress when it cools and it will have a tendency to crack later on at the welds.

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Agreed.
I bit the bullet and signed up for a AI search repository where I could query four at the same time, then do a comparison.
After several question/answers I realized a horizontal fish is better for the load distribution, and far more practical due to the existing gusset overlapping the front 1/2 of the mount and the existing fish from the frame mods by Centurion.
The consensus analysis agreed.

4. Consensus Points​

Across all four responses, the following points align:

• A centered horizontal fish plate is not feasible due to the existing gusset.
• Reinforcement must still occur, but via alternative methods.
• Load spreading is essential to avoid frame cracking at the new hanger.
• Existing frame modifications introduce risk, uncertainty, and complexity.
• Any added reinforcement should consider:
  • proper plate thickness
  • bolt grade (if bolted)
  • good welding practices (if welded)

That works out best, as I already have a piece of 3/8" steel 2" wide.
I'll install 1- 6" long piece in front and behind each forward mount for a little extra support.
I can only access the outside of the frame for welding, and only get clear welding access to the middle in order to get a clear view of the top welds, just barely, turning my head sideways and pressing the helmet into the truck body.
I don't want to chance any blind welds.
Well now, that takes care of the first two out of eight hangers.
With luck this one day axle swap should be done by early February? lol

 

[WMO4IDI]

Certified welder here (CWB Mig, Flux & Stick, all positions, 23+ years)

I'd be more worried about that shotty (illegal) weld on the frame. It was done with a stick, vertical down hand with a lack of deposition (undercutting). The reinforcement plate behind it weakens the frame more than anything with those vertical welds.

Your best bet would be to grind the outside weld flush and add a 3/8" trapezoidal shaped plate over it with a few grade 8, 1/2" minimum bolts to reinforce it.

As mentioned above, the holes can be plugged & re-drilled. An aluminum backing plate can help you avoid "keyholing" while filling them, just knock it off after with a hammer & chisel afterwards and if you're feeling fancy, clean the backside with a die grinder.

I've seen a lot worse, you got this!

 

[03wr250f]

you got better advice than i could have given for the frame repair

as far as the skys bracket and the spacer goes on a stock truck you press out the frame jig nubbin that was used for holding the frame to the assembly line

the only reason they use the spacer is to give it rotational stability, and to give you something to clamp against, because if you use the factory spring hanger holes (f350 ) the lower edge of the bracket hangs 1/2"!lower than the frame

if you have the clearance i dont see why you cant move the bracket up provided it doesn't hit the body. given the curve in your frame you might have to even use a angled shim to match curve