Rear Bumper/Spare Tire Mount Thoughts

[grumpin]

Turns out I can type, albeit slowly. But I can TurboCAD almost as well as w/o burned fingers. And today I got the trail jack drawn up and properly placed. Turns out that there is just enough room between the tire and the tailgate.

And, with some testing I got it where it doesn't obscure the tail light and doesn't hit it when the swing arm is fully open. But that wasn't the case initially.

It fits pretty well just ahead of the spare. And, by removing the top end of the jack it doesn't stick up in the air - although I don't have a pic to prove that.

Anyway, check it out in Projects, or even better on the webpage.

Very cool!

And the front end should be on the ground when you sit in it...

[Gary Lewis]

Very cool!

And the front end should be on the ground when you sit in it...

The 4 x 6" bumper was going to be something like 96 lbs by itself, so a 4 x 5" should be 80 lbs. The swing arm, including the angled pieces, is going to be pushing 100 lbs. I think the tire and wheel will go 85 lbs as the tire alone is 62 lbs. And the jack is 26 lbs. That's almost 300 lbs and doesn't include several things.

And all of that weight is well behind the rear axle, so the rear may be down a bit and the front up.

[grumpin]

The 4 x 6" bumper was going to be something like 96 lbs by itself, so a 4 x 5" should be 80 lbs. The swing arm, including the angled pieces, is going to be pushing 100 lbs. I think the tire and wheel will go 85 lbs as the tire alone is 62 lbs. And the jack is 26 lbs. That's almost 300 lbs and doesn't include several things.

And all of that weight is well behind the rear axle, so the rear may be down a bit and the front up.

 

All kidding aside, I think that's good for the lighter end of the truck, especially off roading.

[Gary Lewis]

The 4 x 6" bumper was going to be something like 96 lbs by itself, so a 4 x 5" should be 80 lbs. The swing arm, including the angled pieces, is going to be pushing 100 lbs. I think the tire and wheel will go 85 lbs as the tire alone is 62 lbs. And the jack is 26 lbs. That's almost 300 lbs and doesn't include several things.

And all of that weight is well behind the rear axle, so the rear may be down a bit and the front up.

 

All kidding aside, I think that's good for the lighter end of the truck, especially off roading.

I agree. The tire was already there, and the jack had to go somewhere, and the old bumper and brackets come off. So maybe 1/2 of the weight is additional. And with the weight of the 460, aux battery, winch & winch bumper up front, it isn't all bad to hang this off the rear.

[Steve83]

I had planned to design it to carry a 44" tire... But that puts the top of a 31" tire 12" above the top of the tailgate...

It doesn't take much to make the wheel mounting points adjustable. Either several holes so you can move the lug studs; or a sliding plate for the studs to raise/lower the spare; or several places to bolt the studs' plate to the arm.

The tire carrier is 2 1/2 x 1/4" square tubing.

That's VERY overbuilt. The tube doesn't need to be nearly as wide (horizontally) as it is tall (vertically) because there's not nearly as much force applied horizontally. And the wall doesn't need to be 1/8"; with the right design, 1/16" would be enough.

The swivel is a piece of 2" tubing w/a .120 wall, which will give .010" clearance.

...I'll add a grease fitting...

I don't think 1/100" is enough to ensure the tube will fit over the mount. With 1/4" clearance (total), you could wrap a 1/8" sheet of teflon between them, which would be much more-durable, without collecting dirt or staining the back of the truck like grease will.

Another common hinge (the precursor to the RockStomper hinge) is a spindle & hub that fit the truck (so they can be used as spares in an emergency). If it's a 4WD truck, the hub can have a manual hub lock that also fits the truck as the only catch for the swing arm.

...a little ramp on the bumper, perhaps made of nylon...

In addition, there will be a tab on the arm close to the left end that will catch the bumper so it can't swing too far and hit the tailgate.

If you put a block at the end of the ramp, the arm won't be able to go past. But the hard plastic lubrication is a good idea that you should continue throughout the design. I used it on my grinder stand:

https://supermotors.net/getfile/965222/thumbnail/grinderstank.jpg

Further, I want to put a little catch on the bumper that will pass through a hole in that tab and automatically hold it to the bumper. ... I know that sounds like a belt and braces approach, but that's me.

I still think you should make the automatic catch your MAIN catch, and the difficult one (wing bolt, or whatever) your backup (only for when you know you won't need to get in the t/g for a while).

...I hit it with my leg.

Then put all the catch mechanisms on the arm, going into the bumper.

Also, I have to figure out how to prevent the carrier from pivoting all the way around and slamming into the side of the truck.

Limit cable, or a boss sticking up from the bumper that interferes with the arm near the taillight; or both.

Your design has a lot of extra weight on it. The arm going along the bumper to the other side, and the angle going back up to the spare are redundant. If you use a rectangular tube more like the bumper (e.g., 1 x 3 x 1/16"), it will bear the weight as a simple angled arm coming up from the pivot. The only reason to have anything parallel to the bumper is to mount the catch, and that doesn't need to be as heavy since it will only receive torque - no weight. If you don't like that look, you could run a short piece horizontally along the bumper about to where it will be hidden by the spare, then turn it up to the mounting lugs.

The factory tire carrier on my early Bronco swings around and hits on the side of the vehicle.

It was designed to. There was an optional bracket so it could be bolted to the side of the truck (with the spare mount flipped over the top bar) allowing the t/g to be left open while driving (particularly at low speeds, as on a farm).

...steel and not cast. I could turn it down in the lathe to get a reasonable diameter.

You could also turn the inside of any common Sch.40 steel tube so the bearings would fit into it, and not use the trailer hub. That's essentially what the RockStomper hinge is.

But I'm not happy with the lights... So, if you have some to suggest...

Flexible LED strips are inexpensive on eBay, and can be mounted to a simple flat horizontal lip above the license plate, glowing down onto it. Then you can put any lights that fit between the top & bottom of the plate, and the inside of the wheel. But I wouldn't wire those up to the normal reverse lights because they'll blind other drivers. I'd make them off-road-only. For bright reverse lights that work on- & off-road, mount them under the bumper so they can't possibly shine or glare upward at vehicles behind you.

https://supermotors.net/getfile/885817/thumbnail/02lights.jpg

...a hi-lift jack mounted on the arm.

I wouldn't do that, even though I know it's common.

The only reason the spare is going on the swing arm is because it takes up too much of the bed, and you don't want it hanging down. Neither of those limitations applies to a high-lift because it's so skinny. Put it in the bed, or inside the bumper, or jacked into a locking position on the bumper. It doesn't need to swing, so I wouldn't add that weight.

[Gary Lewis]

I agree. The tire was already there, and the jack had to go somewhere, and the old bumper and brackets come off. So maybe 1/2 of the weight is additional. And with the weight of the 460, aux battery, winch & winch bumper up front, it isn't all bad to hang this off the rear.

Steve - I see I have a response from you, but will address it in my next post.

Bill - Thanks for the measurements. I've added your info to the spreadsheet, shown below, and I think we can make these conclusions:

• The factory bumper holes are a given distance from the top and rear of the frame, although exactly where remains to be seen.

• Given the differences between frames (see below), it isn't going to be possible for one attachment method to fit all frames if you have it attach to the bottom of the frame as well as the normal bumper attachment holes.

• There aren't any "stock" holes in the bottom of the frame. Darth's don't match BB's, even though they appear to be from a very similar hitch that attaches at three points per side. And the receiver that was on Dad's truck attached with only two bolts per side, and in very different locations.

Given that, the only way to make the bumper universal is for it to only attach to the bumper attachment holes. So I called my nephew, who is mechanical engineer, and he says that those 4 bolts are adequate. However, it isn't enough overkill for me so I'm going to have a piece of 1/2" thick by 2 1/2" wide strap welded to the bottom of the tow eyes and drilled to match the holes in BB's frame - as shown in the latest drawings on the Project page. That way the bottom of the frame takes the up/down forces and the side of the frame takes the sideways forces.

But, that arrangement will only work for RCLB F250HD's or 350's, as they share a frame. And the frame on other trucks will either be too tall or too short for these tow eyes to end flush with the bottom. So, if this design were to be made commercially there would either have to be different tow eyes for each frame or we would have to dispense with the strap at the bottom.

Anyway, I think my overall design is done. But I still have some details to work out. For instance, the latches, plural. And how to mount the Rigid Chase light, which I'm pretty sure I want as it'll give me a strong backup light, which these trucks badly need, without embedding trailer lights in the bumper - which I don't want to do.

[85lebaront2]

Steve - I see I have a response from you, but will address it in my next post.

Bill - Thanks for the measurements. I've added your info to the spreadsheet, shown below, and I think we can make these conclusions:

• The factory bumper holes are a given distance from the top and rear of the frame, although exactly where remains to be seen.

• Given the differences between frames (see below), it isn't going to be possible for one attachment method to fit all frames if you have it attach to the bottom of the frame as well as the normal bumper attachment holes.

• There aren't any "stock" holes in the bottom of the frame. Darth's don't match BB's, even though they appear to be from a very similar hitch that attaches at three points per side. And the receiver that was on Dad's truck attached with only two bolts per side, and in very different locations.

Given that, the only way to make the bumper universal is for it to only attach to the bumper attachment holes. So I called my nephew, who is mechanical engineer, and he says that those 4 bolts are adequate. However, it isn't enough overkill for me so I'm going to have a piece of 1/2" thick by 2 1/2" wide strap welded to the bottom of the tow eyes and drilled to match the holes in BB's frame - as shown in the latest drawings on the Project page. That way the bottom of the frame takes the up/down forces and the side of the frame takes the sideways forces.

But, that arrangement will only work for RCLB F250HD's or 350's, as they share a frame. And the frame on other trucks will either be too tall or too short for these tow eyes to end flush with the bottom. So, if this design were to be made commercially there would either have to be different tow eyes for each frame or we would have to dispense with the strap at the bottom.

Anyway, I think my overall design is done. But I still have some details to work out. For instance, the latches, plural. And how to mount the Rigid Chase light, which I'm pretty sure I want as it'll give me a strong backup light, which these trucks badly need, without embedding trailer lights in the bumper - which I don't want to do.

A couple of items, first Darth is a CCLB (not that I think they made any CCSB models in the Bullnose models) and also a DRW model if that made a difference in the frames. Second the 4 3/8" dimension is as close as I could measure since the bumper is attached right now.

On the bolts, they are some big Metric bolts on Darth, on the pre 1985 models they may be SAE bolts.

[Gary Lewis]

I had planned to design it to carry a 44" tire... But that puts the top of a 31" tire 12" above the top of the tailgate...

It doesn't take much to make the wheel mounting points adjustable. Either several holes so you can move the lug studs; or a sliding plate for the studs to raise/lower the spare; or several places to bolt the studs' plate to the arm.

The tire carrier is 2 1/2 x 1/4" square tubing.

That's VERY overbuilt. The tube doesn't need to be nearly as wide (horizontally) as it is tall (vertically) because there's not nearly as much force applied horizontally. And the wall doesn't need to be 1/8"; with the right design, 1/16" would be enough.

The swivel is a piece of 2" tubing w/a .120 wall, which will give .010" clearance.

...I'll add a grease fitting...

I don't think 1/100" is enough to ensure the tube will fit over the mount. With 1/4" clearance (total), you could wrap a 1/8" sheet of teflon between them, which would be much more-durable, without collecting dirt or staining the back of the truck like grease will.

Another common hinge (the precursor to the RockStomper hinge) is a spindle & hub that fit the truck (so they can be used as spares in an emergency). If it's a 4WD truck, the hub can have a manual hub lock that also fits the truck as the only catch for the swing arm.

...a little ramp on the bumper, perhaps made of nylon...

In addition, there will be a tab on the arm close to the left end that will catch the bumper so it can't swing too far and hit the tailgate.

If you put a block at the end of the ramp, the arm won't be able to go past. But the hard plastic lubrication is a good idea that you should continue throughout the design. I used it on my grinder stand:

https://supermotors.net/getfile/965222/thumbnail/grinderstank.jpg

Further, I want to put a little catch on the bumper that will pass through a hole in that tab and automatically hold it to the bumper. ... I know that sounds like a belt and braces approach, but that's me.

I still think you should make the automatic catch your MAIN catch, and the difficult one (wing bolt, or whatever) your backup (only for when you know you won't need to get in the t/g for a while).

...I hit it with my leg.

Then put all the catch mechanisms on the arm, going into the bumper.

Also, I have to figure out how to prevent the carrier from pivoting all the way around and slamming into the side of the truck.

Limit cable, or a boss sticking up from the bumper that interferes with the arm near the taillight; or both.

Your design has a lot of extra weight on it. The arm going along the bumper to the other side, and the angle going back up to the spare are redundant. If you use a rectangular tube more like the bumper (e.g., 1 x 3 x 1/16"), it will bear the weight as a simple angled arm coming up from the pivot. The only reason to have anything parallel to the bumper is to mount the catch, and that doesn't need to be as heavy since it will only receive torque - no weight. If you don't like that look, you could run a short piece horizontally along the bumper about to where it will be hidden by the spare, then turn it up to the mounting lugs.

The factory tire carrier on my early Bronco swings around and hits on the side of the vehicle.

It was designed to. There was an optional bracket so it could be bolted to the side of the truck (with the spare mount flipped over the top bar) allowing the t/g to be left open while driving (particularly at low speeds, as on a farm).

...steel and not cast. I could turn it down in the lathe to get a reasonable diameter.

You could also turn the inside of any common Sch.40 steel tube so the bearings would fit into it, and not use the trailer hub. That's essentially what the RockStomper hinge is.

But I'm not happy with the lights... So, if you have some to suggest...

Flexible LED strips are inexpensive on eBay, and can be mounted to a simple flat horizontal lip above the license plate, glowing down onto it. Then you can put any lights that fit between the top & bottom of the plate, and the inside of the wheel. But I wouldn't wire those up to the normal reverse lights because they'll blind other drivers. I'd make them off-road-only. For bright reverse lights that work on- & off-road, mount them under the bumper so they can't possibly shine or glare upward at vehicles behind you.

https://supermotors.net/getfile/885817/thumbnail/02lights.jpg

...a hi-lift jack mounted on the arm.

I wouldn't do that, even though I know it's common.

The only reason the spare is going on the swing arm is because it takes up too much of the bed, and you don't want it hanging down. Neither of those limitations applies to a high-lift because it's so skinny. Put it in the bed, or inside the bumper, or jacked into a locking position on the bumper. It doesn't need to swing, so I wouldn't add that weight.

Steve - Thanks foe the detailed response. I'll try to address each one, but I'm sure to miss something. And, let me say from the outset that you may be two or three revisions back on the design.

• I have the tire carrier drilled and tapped for 3 bolts of both the 5-lug and 8-lug Ford pattern, so shouldn't that be enough? The bumper is specific to these trucks.

• As for the swing arm, the final plan has the horizontal piece as a 3 1/2 vertical x 2 1/2 horizontal tube with 3/16" walls. The extra height significantly increases the torsional rigidity, which is needed as the jack is only 1/4" from the tailgate, albeit down close to the swivel/hinge.

• The new swivel is a Mega Spindle with tapered roller bearings.

• I have blocks at the end of the swing arm on the left, and on the right end of the bumper to ensure the thing can't hit the body. Both blocks are 1" wide by 1 1/2" deep steel welded to the bumper, so should be sufficient. But I would like to incorporate some Teflon to prevent the powder coat from being rubbed off and rust starting.

• I agree on the latches. And I'm still looking for the right ones, plural, there. I want something automatic and then something that pulls the arm down so it cannot bounce.

• Yes, the whole thing is overbuilt. But that's the way I like to build. That way I have the peace of mind that the receiver is more solid than the current one. That the swing arm won't flex. The frame won't bend, etc. It'll weigh more than it needs to weigh, but I'm ok with that.

• On the lighting, I think I've settled on the Rigid Chase. It is expensive, but it ticks all the boxes in one go. However, I'll have to see if the backup light part is too bright, as you suggested. If so I can add a switch to disable that part until it is needed.

• Jack: I like that it just fits on the arm. And with the new spindle and the design of the arm it won't be too much weight there. But, I do need to provide a way of locking it on.

Anyway, I really do appreciate your input - even if it doesn't look like it. You've helped significantly in this quest, but I think I'm happy with the design at this point - even though it is overbuilt.

However, I'm still looking for latch ideas. And, I'm seriously considering a backup camera as an option to this.

 

[Gary Lewis]

A couple of items, first Darth is a CCLB (not that I think they made any CCSB models in the Bullnose models) and also a DRW model if that made a difference in the frames. Second the 4 3/8" dimension is as close as I could measure since the bumper is attached right now.

On the bolts, they are some big Metric bolts on Darth, on the pre 1985 models they may be SAE bolts.

Yeah, I thought about the CCLB, but they didn't make a short bed - although Jonathan is.

And I understand the problem of measuring with a bumper in place. I think I'll pull the one off BB soon and make SURE I have the dimensions correct. I don't think this new bumper is going to flex very easily.

BB's bolts are SAE. I know 'cause I put new ones on. But the original ones may have been metric. I'll check the bolt hole sizes.

[Steve83]

...5-lug and 8-lug Ford pattern, so shouldn't that be enough? The bumper is specific to these trucks.

I was only talking about adjusting the mounting height for different spare sizes.

...the torsional rigidity, which is needed...

I don't think it'll be as twisty as you seem to think. Particularly if you make it LIGHTER instead of heavier, and SHORTER instead of longer (across the back of the truck).

...something that pulls the arm down so it cannot bounce.

A simple bullet-shaped pin that stabs into a socket in the bumper face will accomplish that, without much weight, complexity, or wear.

Yes, the whole thing is overbuilt. But that's the way I like to build. ... It'll weigh more than it needs to weigh, but I'm ok with that.

I like building things overstrength, but building them overweight makes them weaker (at the mounting points, where the weight has to attach to the truck); and puts more wear on the truck; and reduces braking/accelerating/steering performance; and costs more for no more benefit. So there are many good reasons to keep it as light as it can be, without losing any strength.

...even if it doesn't look like it.

As long as you keep replying to my posts in this thread, I'll assume you're at least considering the points I'm raising. If you stop replying to me, I'll quit posting in this thread, but I won't be offended.

And, I'm seriously considering a backup camera as an option to this.

They're remarkably cheap & effective. I just put one in the '04 CV I swapped my mother into. It's wired into the big touch-screen radio I put in it.

https://supermotors.net/getfile/1138982/thumbnail/20180824_102127.jpg

https://supermotors.net/getfile/1138891/thumbnail/20180819_140111.jpg

Finding a place for the camera will take some effort, but it'll probably be easier than finding room for the display.