Big Blue's Transformation

[ArdWrknTrk]

I was thinking KC-135, but we are on the same page.

I am paranoid about safety, and there is no way I want that trailer hitch to be anything less than what I have now, which is a commercial hitch. It has six 1/2" bolts holding it to the frame while the to-be bumper/hitch will have eight 14mm bolts which are .55" in diameter. So we are gaining a bit there.

And to Jim's question about how to secure the swing arm, I'm back to this approach. The pin latch may be this 1/2" Dia Plunger Premium 'POP' Pull Pin from Amazon, although I'm open to others. Not shown, but it'll ride up a piece of UHMW plastic and drop into a hole in it as a safety latch.

But the bolt will take a bit more thinking. It is a 1/2-13 bolt with a nut Loctited on it to prevent it from coming out, and just enough threads protruding to fully engage a nut welded to the bumper. However, I think I want there to be a top and bottom support so the bolt won't have a chance of coming into the nut at an angle, so will redesign that. But, I want it to be open so that there's no way for water to be getting into the swing arm past the bolt.

Anyway, that's where I am at the moment, but welcome all suggestions, comments, and upgrades.

There's not much depth (chord) to your hitch crossbar that I can see.

At least in comparison to my hitch.

I personally wouldn't trust much tongue weight no matter the 1/4 x 2 1/2 strap going forward on the lower lip of the frame rails.

I could fold that strap flat with a small sledge.

Yes, I do not care how stiff the 1" plate is, bolted to the existing bumper mounts.

As far as I'm concerned you're relying entirely on the shear of the last 5" of the frame (or whatever the distance of the forward-most bolt is)

Everything (bumper, tire mount, hitch and whatever is attached to the hitch has a simple pivoting load path between those two bolts. or maybe between the forward bolt and the point where the weld between the 1" plate and the bottom strap ends.

Get someone to model it.

I don't think that tiny bit of frame is nearly as strong as you think it is.

[Gary Lewis]

There's not much depth (chord) to your hitch crossbar that I can see.

At least in comparison to my hitch.

I personally wouldn't trust much tongue weight no matter the 1/4 x 2 1/2 strap going forward on the lower lip of the frame rails.

I could fold that strap flat with a small sledge.

Yes, I do not care how stiff the 1" plate is, bolted to the existing bumper mounts.

As far as I'm concerned you're relying entirely on the shear of the last 5" of the frame (or whatever the distance of the forward-most bolt is)

Everything (bumper, tire mount, hitch and whatever is attached to the hitch has a simple pivoting load path between those two bolts. or maybe between the forward bolt and the point where the weld between the 1" plate and the bottom strap ends.

Get someone to model it.

I don't think that tiny bit of frame is nearly as strong as you think it is.

Jim - While I don't fully understand everything you said I do understand the overall meaning. Which is basically what I've been worried about as well - the strength of the connection to the rear of the frame, and the strength of that bit of the frame itself.

Your point is that there's not much leverage on the rear of the frame where the two bolts in the side and the two bolts in the bottom are. So regardless of how strong the piece on the bottom is, whether angle or strap, everything is keyed to the last few inches on the frame. Right?

Unfortunately I've not figured out a way to go forward to catch the 3rd bolt hole in the bottom of the frame where the current trailer hitch bolts. The frame bends down just ahead of the 2nd hole, the one you can see near the spring hanger, so no piece of straight material is going to work.

Let me take some more pics today as well as some measurements. That will give me a better understanding of what we are dealing with. And maybe we can come up with a way to make it stronger.

And I'll ask my engineer nephew to see what he thinks. Perhaps he can model it or suggest an upgrade.

[Gary Lewis]

Jim - While I don't fully understand everything you said I do understand the overall meaning. Which is basically what I've been worried about as well - the strength of the connection to the rear of the frame, and the strength of that bit of the frame itself.

Your point is that there's not much leverage on the rear of the frame where the two bolts in the side and the two bolts in the bottom are. So regardless of how strong the piece on the bottom is, whether angle or strap, everything is keyed to the last few inches on the frame. Right?

Unfortunately I've not figured out a way to go forward to catch the 3rd bolt hole in the bottom of the frame where the current trailer hitch bolts. The frame bends down just ahead of the 2nd hole, the one you can see near the spring hanger, so no piece of straight material is going to work.

Let me take some more pics today as well as some measurements. That will give me a better understanding of what we are dealing with. And maybe we can come up with a way to make it stronger.

And I'll ask my engineer nephew to see what he thinks. Perhaps he can model it or suggest an upgrade.

Ok folks, here's one of Jim's points explained. I think. And I hope that the red dimensions show up.

That point, which is well made, is that the current plan gives away a whole bunch of leverage. If you assume that the pivot point is the rear bolts of the tow eye and trailer hitch, which are ~ 1 1/2" forward of the rear of the frame, then you have one bolt that is 3" and another that is 6" farther forward. That's not much leverage.

To this point I've been giving up the bolt hole that is 11" farther forward, and that distance means that it has about 3x the leverage of the one that is 6" forward. The next post will lay out an approach that I hope will take advantage of that leverage.

Also, another thing to note while we are here is that the current hitch is made of 1/4" plate, and that it is 3" tall about where the "11" is, and those dimensions determine its strength, which has been adequate.

In addition, note that the frame turns down just forward of the middle bolt. That puts the forward bolt hole ~1/2" below the rear two holes.

[Gary Lewis]

Ok folks, here's one of Jim's points explained. I think. And I hope that the red dimensions show up.

That point, which is well made, is that the current plan gives away a whole bunch of leverage. If you assume that the pivot point is the rear bolts of the tow eye and trailer hitch, which are ~ 1 1/2" forward of the rear of the frame, then you have one bolt that is 3" and another that is 6" farther forward. That's not much leverage.

To this point I've been giving up the bolt hole that is 11" farther forward, and that distance means that it has about 3x the leverage of the one that is 6" forward. The next post will lay out an approach that I hope will take advantage of that leverage.

Also, another thing to note while we are here is that the current hitch is made of 1/4" plate, and that it is 3" tall about where the "11" is, and those dimensions determine its strength, which has been adequate.

In addition, note that the frame turns down just forward of the middle bolt. That puts the forward bolt hole ~1/2" below the rear two holes.

Ok, let's try this on for size/strength. And please critique, upgrade, or comment.

First, here's a view of the original plan showing how the receiver is welded to the cross piece and the cross piece is welded to the tow eye as well as the piece of angle. And all of those joints are fish plated.

And now, here's Plan D. It is basically the same as the Original Plan but the angle gets turned so the 3" extends down instead of in, which makes it as strong as the current hitch, and it gets repositioned to the inside of the tow eye and directly below the frame. That way it'll clear the spring hanger.

And I've modified the drawing to show the radius of the frame (1/2") and the angle (1/8") to show that there is some clearance for a weld. Plus, I've shown how the angle will be cut and re-welded to handle the 1/2" offset of the front hole.

And remember that this is all one assembly. The receiver and the tow eyes are both welded to the 1/4" thick bumper in both the front and rear. And the receiver is welded to the cross piece, which is also welded to the angles and the tow eyes and fish plates.

So with the 3" x 1/4" angle taking the place of the current hitch I think the whole assembly is stronger than the current hitch, and much stronger than the current bumper.

Thoughts?

[Gary Lewis]

Ok, let's try this on for size/strength. And please critique, upgrade, or comment.

First, here's a view of the original plan showing how the receiver is welded to the cross piece and the cross piece is welded to the tow eye as well as the piece of angle. And all of those joints are fish plated.

And now, here's Plan D. It is basically the same as the Original Plan but the angle gets turned so the 3" extends down instead of in, which makes it as strong as the current hitch, and it gets repositioned to the inside of the tow eye and directly below the frame. That way it'll clear the spring hanger.

And I've modified the drawing to show the radius of the frame (1/2") and the angle (1/8") to show that there is some clearance for a weld. Plus, I've shown how the angle will be cut and re-welded to handle the 1/2" offset of the front hole.

And remember that this is all one assembly. The receiver and the tow eyes are both welded to the 1/4" thick bumper in both the front and rear. And the receiver is welded to the cross piece, which is also welded to the angles and the tow eyes and fish plates.

So with the 3" x 1/4" angle taking the place of the current hitch I think the whole assembly is stronger than the current hitch, and much stronger than the current bumper.

Thoughts?

Not to sidetrack things, but after getting the bumper back on I had a little time and energy left so decided I'd try my hand at boring out the big hole on one of the tow eyes. The holes weren't round nor smooth, and I wanted them to be both. But it isn't easy to set up on the mill as there's really no center.

Here's a shot of both of them and I think you can tell which one I've bored out. And you can see an area of the top one that is rough. The one I bored out was worse and I had to take it out to 1.160" from roughly 1.050" to get it cleaned up. I don't think the size matters, and I think it'll clean up nicely.

[Bruce moose4x4]

Not to sidetrack things, but after getting the bumper back on I had a little time and energy left so decided I'd try my hand at boring out the big hole on one of the tow eyes. The holes weren't round nor smooth, and I wanted them to be both. But it isn't easy to set up on the mill as there's really no center.

Here's a shot of both of them and I think you can tell which one I've bored out. And you can see an area of the top one that is rough. The one I bored out was worse and I had to take it out to 1.160" from roughly 1.050" to get it cleaned up. I don't think the size matters, and I think it'll clean up nicely.

What about moving the main plates inside the frame rail and run them farther back, could even catch a few of the hanger bolts.

[Gary Lewis]

What about moving the main plates inside the frame rail and run them farther back, could even catch a few of the hanger bolts.

Good question, but there's a riveted-in crossmember at the back of the fuel tank, which is about where the spring hanger is, and there's no way to get past it on the inside of the frame. That's why I have the plates on the outside.

So, what are your thoughts about Plan D?

[Bruce moose4x4]

Good question, but there's a riveted-in crossmember at the back of the fuel tank, which is about where the spring hanger is, and there's no way to get past it on the inside of the frame. That's why I have the plates on the outside.

So, what are your thoughts about Plan D?

If your not going to use your receiver hitch that is on there? Could you cut the top of the frame mount off and make it the angle and move it to the opposite side? Then you might be able to use all three mounting bolts then?

[Gary Lewis]

If your not going to use your receiver hitch that is on there? Could you cut the top of the frame mount off and make it the angle and move it to the opposite side? Then you might be able to use all three mounting bolts then?

I actually thought about that, but I've promised it to Scott.

And, Plan D does use all three of the lower bolt holes on the bottom of the frame on each side. So instead of the hitch using six bolts it'll really be using ten, including the four on the side of the frame holding the tow eyes on.

[ArdWrknTrk]

Ok folks, here's one of Jim's points explained. I think. And I hope that the red dimensions show up.

That point, which is well made, is that the current plan gives away a whole bunch of leverage. If you assume that the pivot point is the rear bolts of the tow eye and trailer hitch, which are ~ 1 1/2" forward of the rear of the frame, then you have one bolt that is 3" and another that is 6" farther forward. That's not much leverage.

To this point I've been giving up the bolt hole that is 11" farther forward, and that distance means that it has about 3x the leverage of the one that is 6" forward. The next post will lay out an approach that I hope will take advantage of that leverage.

Also, another thing to note while we are here is that the current hitch is made of 1/4" plate, and that it is 3" tall about where the "11" is, and those dimensions determine its strength, which has been adequate.

In addition, note that the frame turns down just forward of the middle bolt. That puts the forward bolt hole ~1/2" below the rear two holes.

I'm back to where I can reply, and I'm going to try and get a new phone tomorrow (if the storm doesn't interfere)

Plan D does start to make up for the depth you lose from the existing hitch.

The cut on the left is not going to get you back to horizontal, it's going to double the pitch of the first pie slice.

It's the dimension from where the bolt is through the frame to the very bottom that counts with current hitch.

The bolts act in shear for tugging loads but in tension for tongue weight and other vertical loads.

So the full lever arm is from the ball, but the resistance is from the rear bolt to the front bolt.

Having that bolt forward makes a big difference.