Nothing Special's '71 Bronco

[Nothing Special]

If it goes under the Atlas to be the skid plate then I think it has to sit lower than if it is just reinforcement. So what if it was two parts - the one I show that is wider than the frame rail by ~2", and a skid plate that bolts onto that with spacers that drop it down enough to go under the Atlas.

The ~2" lip, sticking in, is to bolt to. But that also means it'll have to go lower than if it was just the width of the frame.

On the other hand, if the strap was just the width of the frame but was thick enough I think you might get by with two holes in it to bolt to. That would minimize the drop in the strap, but then you'd have even more of a need for spacers to get the skid plate under the Atlas.

I really appreciate the different ideas, and now is a good time to get them out. But I'll warn you that I'm not going to put much more detailed thought into it until I get closer to actually building it. Right now my mind's moved on to getting the axle out, getting the radius arm mounts back to stock and getting the new axle modified and in place. Then after I have it sitting on its own tires again I'll get back to the skid plate and reinforcing the frame.

That said, I will think about it a little more now. I'm envisioning the skid plate being tight against the bottom of the fame rails to maximize ground clearance there, and dropping down as needed to clear the transfer case. Of course I also want smooth transitions on the bottom of the skid plate so it doesn't act as a grappling hook, grabbing hold of every rock it touches. So we'll see if what I envision ends up materializing. But if it does, the skid plate will be close enough to the frame rail to be the reinforcement (whether it can be attached well enough to be the reinforcement is a different still unanswered question).

[Nothing Special]

In my Home Movies thread Gary asked:

....

So, when do you head to Moab? What changes are you making before then? Not that this is the thread for that, but...

That may not be the thread for this, but this thread is, so...

The plan this winter / spring is a pretty major redo of the front suspension (among other things). The goal that started all of this is getting my radius arm mounts up higher. I lowered them a long time ago to fix my caster problems, but they are now a limiting factor. I high-center on them pretty frequently. But raising the radius arm mounts isn't something I can just do. I don't know if you're familiar with the concept of a snowball in projects like these??? So the way it goes is...

Raise the radius arm mounts to gain clearance.

But that makes the transfer case the lowest point (with no skid plate). I can clock the transfer case higher, but it will hit the frame rail. So...

I need to notch out the frame (and then reinforce it obviously) to make room for the transfer case.

Also my front driveshaft U-joint angle is currently maxed out, so moving the transfer case front output higher means I need to move the other end of the driveshaft higher too. I plan to do that in two ways.

I'm not sure what lift I currently have. I think it's about 3.5", but possibly a bit more. That gives me room for at least 35" tires, maybe 37". But Lesley tells me that I'm not going bigger than 33" tires if I want her to keep coming with me. So I'm planning on putting a shorter lift on it, maybe 1.5" - 2.5". That will hurt my breakover angle a little, but I'll gain closer to 4" - 6" from the radius arm mount change, so it's still a big net gain.

But that won't get my U-joint angle low enough, so the other change planned is to rotate the differential forward to raise the pinion. In addition to improving the U-joint angle in the double Cardan joint at the transfer case that will also let me get the angle in the single Cardan U-joint at the diff closer to zero, which will help with the driveline vibration I now have in 4WD.

However rotating the axle forward will mess up my caster even more than just raising the radius arm mounts will. And remember, I did that to fix a caster problem originally. So the plan now is to cut the inner "C"s off the axle ends and turn them back to fix the camber.

By the way, doing all of that to the front axle begs the question "why not switch to a high pinion diff?" I've thought about that, and while it would be good for U-joint angles, driveshaft clearance and gear strength, "they say" that you need at least a 4" - 6" lift to get a high pinion diff to clear the oil pan. Lesley doesn't want the Bronco to be any higher so that much lift isn't an option, so I'm sticking with the low pinion.

Oh, and putting a skid plate under the transfer case seems like a good idea now too.

(I'm sure you have no experience with scope creep like that!)

... and yes, in the post above I did say "new axle." Because even though I previously said...

.... By the way, doing all of that to the front axle begs the question "why not switch to a high pinion diff?" I've thought about that, and while it would be good for U-joint angles, driveshaft clearance and gear strength, "they say" that you need at least a 4" - 6" lift to get a high pinion diff to clear the oil pan. Lesley doesn't want the Bronco to be any higher so that much lift isn't an option, so I'm sticking with the low pinion....

... I'm going to try to put a high pinion axle in it. In more conversations on an early Bronco forum I've now heard that 3.5" lift is enough for a high pinion, and I'm pretty close to that. Also I've heard at least once that it's the oil pan of the C4 automatic that's the issue, not the engine oil pan, and I don't have a C4. Looking at what room I have I can't imagine I'm going to have trouble with any interference with the oil pan or the NV3550 trans.

So today I got these:

I really only wanted one, but the first axle the junk yard pulled had water in it so they stripped it down to find out what it looked like inside. The gears were rusty, so they pulled another one. That wasn't the right one* (fortunately I talked with them before they shipped it) so they found another that was correct and said they'd ship that. But since I had told them that I really didn't care if the gears were rusty I guess they decided to sent the first housing to me as well. Anyway, I got everything i expected and more, so soon it will be time to start putting a high pinion axle together!

* And on "the right one," Up through 1975 F-100s and F-150s (if 150s existed yet) had drum brakes in front. In '78 and '79 they had cast axle tubes that had the wedges integrally cast with the tubes, so you can't cut them off and weld them back on. So '76 and '77 are "the right years" to get. You get all of the parts needed to put disk brakes on and tubes you can more reasonably modify. Plus I think the '76 - '77 are the largest diameter, thickest wall tubes, so you also get the strongest housing.

And yes, even though I already have disk brakes on my stock axle, I need new parts for this one. My Bronco came with drum brakes, and the easiest way to convert to disks in front is to use a combination of aftermarket parts and parts off a Chevy truck. While I might be able to put my old knuckles on the high pinion Cs, using all '76 - '77 F-150 parts makes for a simpler system. And it also gives me stronger outer axle stubs than the '71 Bronco parts.

 

[Gary Lewis]

... and yes, in the post above I did say "new axle." Because even though I previously said...

.... By the way, doing all of that to the front axle begs the question "why not switch to a high pinion diff?" I've thought about that, and while it would be good for U-joint angles, driveshaft clearance and gear strength, "they say" that you need at least a 4" - 6" lift to get a high pinion diff to clear the oil pan. Lesley doesn't want the Bronco to be any higher so that much lift isn't an option, so I'm sticking with the low pinion....

... I'm going to try to put a high pinion axle in it. In more conversations on an early Bronco forum I've now heard that 3.5" lift is enough for a high pinion, and I'm pretty close to that. Also I've heard at least once that it's the oil pan of the C4 automatic that's the issue, not the engine oil pan, and I don't have a C4. Looking at what room I have I can't imagine I'm going to have trouble with any interference with the oil pan or the NV3550 trans.

So today I got these:

I really only wanted one, but the first axle the junk yard pulled had water in it so they stripped it down to find out what it looked like inside. The gears were rusty, so they pulled another one. That wasn't the right one* (fortunately I talked with them before they shipped it) so they found another that was correct and said they'd ship that. But since I had told them that I really didn't care if the gears were rusty I guess they decided to sent the first housing to me as well. Anyway, I got everything i expected and more, so soon it will be time to start putting a high pinion axle together!

* And on "the right one," Up through 1975 F-100s and F-150s (if 150s existed yet) had drum brakes in front. In '78 and '79 they had cast axle tubes that had the wedges integrally cast with the tubes, so you can't cut them off and weld them back on. So '76 and '77 are "the right years" to get. You get all of the parts needed to put disk brakes on and tubes you can more reasonably modify. Plus I think the '76 - '77 are the largest diameter, thickest wall tubes, so you also get the strongest housing.

And yes, even though I already have disk brakes on my stock axle, I need new parts for this one. My Bronco came with drum brakes, and the easiest way to convert to disks in front is to use a combination of aftermarket parts and parts off a Chevy truck. While I might be able to put my old knuckles on the high pinion Cs, using all '76 - '77 F-150 parts makes for a simpler system. And it also gives me stronger outer axle stubs than the '71 Bronco parts.

Cool! I'm subscribed. Now where's that popcorn-eating emoticon...

On the frame/skid plate, I think it is good to get several ideas in mind up front and then you can think about them as the project progresses. Sometimes things will fall into place and you'll said "Yep, that will work."

[FuzzFace2]

If it goes under the Atlas to be the skid plate then I think it has to sit lower than if it is just reinforcement. So what if it was two parts - the one I show that is wider than the frame rail by ~2", and a skid plate that bolts onto that with spacers that drop it down enough to go under the Atlas.

The ~2" lip, sticking in, is to bolt to. But that also means it'll have to go lower than if it was just the width of the frame.

On the other hand, if the strap was just the width of the frame but was thick enough I think you might get by with two holes in it to bolt to. That would minimize the drop in the strap, but then you'd have even more of a need for spacers to get the skid plate under the Atlas.

I was talking of boxing in the opening to the inside of the frame making like a pocket the case would fit into like it dose now. Think of it like the 460 oil filter notch on the frames to clear the filter but a little more square. I think this would add back some strength to the frame.

Then the skid plate from side to side to add more strength.

Not knowing just what you have going on there on the skid plate & edge of frame maybe you could add angle iron welded to the outer edge (could point down) that maybe the bolts would go through as that should also add strength.

The Jeep YJ mounts the trans / transfer to the skid plate that runs side to side and is bolted to the bottom of the frame. The only thing they did wrong was use nut certs and years later when you have to drop everything the nut certs would spin so you would then need to cut the bolt(s) off and figure a way to bolt the plate back on.

How do I know this you ask? My son went through this on his.

I also told him once the nut certs were out to make the holes bigger so a normal nut would fit in the hole and weld it in place. Then when putting it back together to never seize the bolts.

I think he only did 1 like that dont remember what he did on the others?

Dave ----

[Nothing Special]

I was talking of boxing in the opening to the inside of the frame making like a pocket the case would fit into like it dose now. Think of it like the 460 oil filter notch on the frames to clear the filter but a little more square. I think this would add back some strength to the frame.

Then the skid plate from side to side to add more strength.

I'm definitely planning on that. Stealing Gary's sketch from a few posts back, I'm planning on welding small plates at the top and sides of the cut-out (all three of the thin black lines). Those plates will be welded to the cut edges on the inside face of the frame and to the inside of the outer face, as well as to each other where the top and side pieces meet. I might also weld a vertical plate in from the bottom of the cut up to the top piece I will add. But I agree with Gary's point that all of that won't entirely make up for what cutting the lower flange lost. So hopefully I can figure out how to do that with the skid plate.

https://forum.garysgaragemahal.com/file/n117541/Bobs_Frame_Stiffener.jpg

Not knowing just what you have going on there on the skid plate & edge of frame maybe you could add angle iron welded to the outer edge (could point down) that maybe the bolts would go through as that should also add strength.

I'll file this with ideas to think about when I'm back to thinking about this.

The Jeep YJ mounts the trans / transfer to the skid plate that runs side to side and is bolted to the bottom of the frame. The only thing they did wrong was use nut certs and years later when you have to drop everything the nut certs would spin so you would then need to cut the bolt(s) off and figure a way to bolt the plate back on.

How do I know this you ask? My son went through this on his.

I also told him once the nut certs were out to make the holes bigger so a normal nut would fit in the hole and weld it in place. Then when putting it back together to never seize the bolts.

I think he only did 1 like that dont remember what he did on the others?

Dave ----

Yeah, I won't be using nutserts!

I don't want to use the skid plate as the trans mount crossmember. I want to be able to take the skid plate off without worrying about supporting anything else. I've definitely seen it done that way, but it's not what I want to do.

 

[Bruce moose4x4]

I was talking of boxing in the opening to the inside of the frame making like a pocket the case would fit into like it dose now. Think of it like the 460 oil filter notch on the frames to clear the filter but a little more square. I think this would add back some strength to the frame.

Then the skid plate from side to side to add more strength.

I'm definitely planning on that. Stealing Gary's sketch from a few posts back, I'm planning on welding small plates at the top and sides of the cut-out (all three of the thin black lines). Those plates will be welded to the cut edges on the inside face of the frame and to the inside of the outer face, as well as to each other where the top and side pieces meet. I might also weld a vertical plate in from the bottom of the cut up to the top piece I will add. But I agree with Gary's point that all of that won't entirely make up for what cutting the lower flange lost. So hopefully I can figure out how to do that with the skid plate.

https://forum.garysgaragemahal.com/file/n117541/Bobs_Frame_Stiffener.jpg

Not knowing just what you have going on there on the skid plate & edge of frame maybe you could add angle iron welded to the outer edge (could point down) that maybe the bolts would go through as that should also add strength.

I'll file this with ideas to think about when I'm back to thinking about this.

The Jeep YJ mounts the trans / transfer to the skid plate that runs side to side and is bolted to the bottom of the frame. The only thing they did wrong was use nut certs and years later when you have to drop everything the nut certs would spin so you would then need to cut the bolt(s) off and figure a way to bolt the plate back on.

How do I know this you ask? My son went through this on his.

I also told him once the nut certs were out to make the holes bigger so a normal nut would fit in the hole and weld it in place. Then when putting it back together to never seize the bolts.

I think he only did 1 like that dont remember what he did on the others?

Dave ----

Yeah, I won't be using nutserts!

I don't want to use the skid plate as the trans mount crossmember. I want to be able to take the skid plate off without worrying about supporting anything else. I've definitely seen it done that way, but it's not what I want to do.

I read your not thinking a whole lot on strengthening the frame But I wanted to give you my thoughts.

Cut a heavy piece of angle or another section of frame. make it long enough to span the hole you cut out, I would make it as long as you could to go inside the frame rail with the back towards the outside of the frame and along the bottom of the frame. Drill or cut some holes in the outside of the frame and along the bottom and plug weld the angle to the frame. once ground down on the outside of the frame no interference with the side tank. You might have to radius the corner of the angle iron to get it to fit snug against the interior frame wall. That is why I mentioned using another piece of frame rail that has the radius. If you need a piece I have some old frame rail pieces laying around I could cut to your size and send you.

Looking forward to seeing the conclusion of this build. If you ever get back to SMORR let me know, I only live 30 miles from there.

[Nothing Special]

I read your not thinking a whole lot on strengthening the frame But I wanted to give you my thoughts.

Cut a heavy piece of angle or another section of frame. make it long enough to span the hole you cut out, I would make it as long as you could to go inside the frame rail with the back towards the outside of the frame and along the bottom of the frame. Drill or cut some holes in the outside of the frame and along the bottom and plug weld the angle to the frame. once ground down on the outside of the frame no interference with the side tank. You might have to radius the corner of the angle iron to get it to fit snug against the interior frame wall. That is why I mentioned using another piece of frame rail that has the radius. If you need a piece I have some old frame rail pieces laying around I could cut to your size and send you.

Looking forward to seeing the conclusion of this build. If you ever get back to SMORR let me know, I only live 30 miles from there.

I'm not quite following you. Are you talking about putting steel inside the original frame rail? If so, that sounds challenging, and I'm not sure it buys me anything. I've got room for a plate on the outside, just probably not for a C-channel with the opening to the outside. And what I need to do is replace the beef I had to cut out of the bottom flange. But I can't do that by just putting new metal there, I need the cut-out for my transfer case. So I'm thinking something like Gary sketched will be my best bet. Then it's a question of how to integrate that with the skid plate.

[Bruce moose4x4]

I'm not quite following you. Are you talking about putting steel inside the original frame rail? If so, that sounds challenging, and I'm not sure it buys me anything. I've got room for a plate on the outside, just probably not for a C-channel with the opening to the outside. And what I need to do is replace the beef I had to cut out of the bottom flange. But I can't do that by just putting new metal there, I need the cut-out for my transfer case. So I'm thinking something like Gary sketched will be my best bet. Then it's a question of how to integrate that with the skid plate.

Yes an angle inside the frame rail plug welded like you did your rock sliders. With the angle inside would create no interference issues. You could then box the hole you cut like you planed.

[Bruce moose4x4]

16504176274521555276090.jpg

Yes an angle inside the frame rail plug welded like you did your rock sliders. With the angle inside would create no interference issues. You could then box the hole you cut like you planed.

The pic is not rotated correctly. Did that on my phone, But maybe it will be a little clearer.

[Nothing Special]

The pic is not rotated correctly. Did that on my phone, But maybe it will be a little clearer.

Thanks for the picture. It's definitely good to have more stuff to think about.