Structural Questions

[drcomanche]

I have a few questions and since they're all related, I put them under one thing here.

Question 1:  First of all, and be honest with me here, how stupid of an idea is it to fix my floors to the edge of the frame rail interiors and then have a boltable plate that goes over top of the frame channel? I know it would allow water in(not that the old floor didn't already) but they get wet anyway and I think being able to have access to the inside of one of the most critical areas is pretty useful. I'm thinking welding the bolts from under the frame rail lip and then having a good sized plate overtop. I have no idea how this will effect the overall strength of the unibody, or if my plating the frame will have any effect on that. I can't imagine that the old floor lended much structural advantage. 

 

Question 2: How much support is need to take the place of the torque boxes? I know no one will have an exact answer, but I'm open to some opinions on how to replace the rigidity they offered. I am welding in 3 steel square tubes from my solid rock rails to the frame in roughly the places they are at(with the addition of one more). Will that be enough?

 

 

Question 3:   There are some braces right along the seem of the frame rail inside. They seem to be integral in holding the spot welded seem together. My intention with the truck is to weld that seem completely and then plate across it. So the question is, are they necessary after the bits and pieces are welded on? I want to get the rust out from underneath them, but that's proving difficult and I don't want it to come back later due to poor preparation. It also lets me put a more stable plate for the skid plate bolts to weld onto. Or maybe cutting just the bottom segments out and leaving the side(and welding them up too). They don't seem to be well attached on the bottom bit.

 

The braces in question

 

[Jeep Driver]

Of course I'm not going to give you a satisfactory answer, that's a given. 

 

I suspect that tooling is at question here?

In my case I have some custom body work aspirations of my own, I'm spending a lot of time studying from the masters. Guys who build custom cars/trucks from scratch, it's from that POV that any answer I would give would come from. 

 

My answer would be to put it back exactly like you found it, once restored, then consider adding strength. 

As I'm finding out myself, metal forming is an art and it's expensive, tooling is expensive. 

 

Just my opinion, Ironmanfab is the only one who is truly taking a stab at structural integrity, take a look at his longarm/4link set up, pretty damn nice (barring that awful blue paint). 

[drcomanche]

Yeah, I know it's kind of a toss up. A bit like playing with fire when you start tearing into frame parts. The only real fabrication I'll be doing is the outer sleeve and plating(accept for the floor, but that's not a big deal). I do have the added issue that some parts just aren't salvageable, and some are blocking vital areas that need to be accessed. Just testing the waters and seeing what people think and what's possible.

[Pete M]

the top cap of the frame (above the floor) is frequently discarded and not replaced

[AZJeff]

On 8/18/2018 at 10:40 AM, drcomanche said:

I have a few questions and since they're all related, I put them under one thing here.

 

Question 2: How much support is need to take the place of the torque boxes? I know no one will have an exact answer, but I'm open to some opinions on how to replace the rigidity they offered. I am welding in 3 steel square tubes from my solid rock rails to the frame in roughly the places they are at(with the addition of one more). Will that be enough?

 

 

How large are the braces you are running from the rock rails to the "frame" rail?   If they are 2" square tube or bigger, those can replace the torque boxes, provided you actually tie those braces not only to the frame rail, but to the floorpan as well.   The torque boxes are intended to tie the rocker panel area of the cab to the "frame" rails.  Your braces would accomplish the same thing, as long as they are big enough and located in a similar position along the length of the "Frame" rail.

[AZJeff]

On 8/18/2018 at 10:40 AM, drcomanche said:

I have a few questions and since they're all related, I put them under one thing here.

 

Question 3:   There are some braces right along the seem of the frame rail inside. They seem to be integral in holding the spot welded seem together. My intention with the truck is to weld that seem completely and then plate across it. So the question is, are they necessary after the bits and pieces are welded on? I want to get the rust out from underneath them, but that's proving difficult and I don't want it to come back later due to poor preparation. It also lets me put a more stable plate for the skid plate bolts to weld onto. Or maybe cutting just the bottom segments out and leaving the side(and welding them up too). They don't seem to be well attached on the bottom bit.

 

The braces in question

 

Those look to be some sort of doubler used to tie to sections of the "frame" rail together.    It would say having a piece in that area that performs that function is probably structurally critical.   If you are worried about the area between those doublers and the bottom of the "frame" rail,  you can do a few things:

 

1.  try to etch the area between the two pieces with some sort of acid to remove any existing rust.  Then THOROUGHLY neutralize the acid and allow it to dry.   Then apply POR15 into the joint to allow that specialized paint to convert the remaining rust into a neutral state.

 

2.  cut ONLY the bottom surface of the frame rail off, and clean the bottom of those doublers of any rust.  Then weld on new steel of at least the same guage or heavier on the outside.   You can also go in and weld those doublers to the new bottom surface of the frame rail from the inside.  You might need to make some holes in those doublers before installing the new bottom of the frame rail, and then do some plug welds between the doublers and the new bottom surface.

 

3.  remove the existing doublers from inside the "frame" rail, and clean the floor of the frame rail in the area you say cannot be reached now.  Then make new doublers from appropriate guage metal, and weld them into the frame rails inside.

 

Whatever approach you choose, don't just remove those doublers and call it a day.  Those are pretty important in that area.

[drcomanche]

14 hours ago, AZJeff said:

How large are the braces you are running from the rock rails to the "frame" rail?   If they are 2" square tube or bigger, those can replace the torque boxes, provided you actually tie those braces not only to the frame rail, but to the floorpan as well.   The torque boxes are intended to tie the rocker panel area of the cab to the "frame" rails.  Your braces would accomplish the same thing, as long as they are big enough and located in a similar position along the length of the "Frame" rail.

They would be 2 or bigger. The 2 forward braces are in a position where they pop up through the floor boards, so they would be directly welded. The rear one would have the upper area of the cab, which is it's own boxed in frame "rail" of sorts, and the stock torque boxes on the inside of the frame.

 

14 hours ago, AZJeff said:

Those look to be some sort of doubler used to tie to sections of the "frame" rail together.    It would say having a piece in that area that performs that function is probably structurally critical.   If you are worried about the area between those doublers and the bottom of the "frame" rail,  you can do a few things:

 

1.  try to etch the area between the two pieces with some sort of acid to remove any existing rust.  Then THOROUGHLY neutralize the acid and allow it to dry.   Then apply POR15 into the joint to allow that specialized paint to convert the remaining rust into a neutral state.

 

2.  cut ONLY the bottom surface of the frame rail off, and clean the bottom of those doublers of any rust.  Then weld on new steel of at least the same guage or heavier on the outside.   You can also go in and weld those doublers to the new bottom surface of the frame rail from the inside.  You might need to make some holes in those doublers before installing the new bottom of the frame rail, and then do some plug welds between the doublers and the new bottom surface.

 

3.  remove the existing doublers from inside the "frame" rail, and clean the floor of the frame rail in the area you say cannot be reached now.  Then make new doublers from appropriate guage metal, and weld them into the frame rails inside.

 

Whatever approach you choose, don't just remove those doublers and call it a day.  Those are pretty important in that area.

I was going to cut them out, but not all the way to the seem, and only the bottom parts. They aren't attached to the bottom in any way, just kind of free floating a quarter of an inch above(with a bunch of rust between). No matter what I do, the vertical pieces would have a full weld on the inner frame rail and the outer seem would be a full weld, too. Then, on top of that, the frame rails would be sleeved around that area, and plated on the rest of the truck.

[AZJeff]

1 hour ago, drcomanche said:

They would be 2 or bigger. The 2 forward braces are in a position where they pop up through the floor boards, so they would be directly welded. The rear one would have the upper area of the cab, which is it's own boxed in frame "rail" of sorts, and the stock torque boxes on the inside of the frame.

 

I was going to cut them out, but not all the way to the seem, and only the bottom parts. They aren't attached to the bottom in any way, just kind of free floating a quarter of an inch above(with a bunch of rust between). No matter what I do, the vertical pieces would have a full weld on the inner frame rail and the outer seem would be a full weld, too. Then, on top of that, the frame rails would be sleeved around that area, and plated on the rest of the truck.

If you are sleeving the frame rails already, then I think you will be good to go.

[zomeizter]

Don't be scared to tear into the structure, go for it, just ensure you beef up on the critical supporting areas. It is very good to mimic what the factory did but there's always room for improvement/overkill. Clean the rust well before you weld and if possible, keep water intrusion in check, seal everything with welding or pucky.