Jump to content
Bullnose Forums

Rear Bumper/Spare Tire Mount Thoughts


Gary Lewis

Recommended Posts

I see no major flaws. Personally I think having to turn a screw out and then back in again would be more effort than I'd want to do to open the tailgate. I don't see a great way around that with your goals and constraints. And of course it's not me that needs to do it, so take it for what it's worth.

And a thought from someone else's design (maybe that early Bronco I linked before?), I read that someone wanted the spare tire as far to the left as possible. He thought it would be less in the way of visibility if it was right behind the driver. I'm not sure if I completely agree wit hthat, but it makes some sense to me at least. To see behind you the middle is probably most important. And for lane changes you want to be able to see over the right end of the gate, but to the left you're going to look out the side window. Anyway, just a thought. If you chose to do that (and I'm not saying you should), you could mirror it to put the pivot on the driver's side, and move the tire as far over as you could without the tire hitting the bed when it swings open. (Might give you room for the DeStaco clamp on the end again?)

Thank you for the review!

I've thought about it long and hard, and I don't think I want to move the tire from the center. The main reason is that I have the jack mounted on top of the swing arm and with the current position of the tire in the center the jack, w/o the bit on the end, just stops at the top of the tailgate. But, if the tire moves to the side it'll change the angle of the upper swing arm and the jack will stick way up in the air.

And, I do plan to put a rear-view camera on the truck. I don't like the idea of having the spare tire behind the bumper and just waiting to be the first thing that hits - and then it will hit the tailgate. On the other hand, it isn't nearly as far back as many I've seen on the road as people frequently use a spare tire carrier that goes into the receiver, and those put the tire typically another 6" to 12" further aft. So my approach isn't as bad, but I still want the camera.

As for the screw, it is fiddly. But, I don't think I'll be opening the tailgate all that much to make it a real pain. And, the knowledge that it is very secure and won't be coming loose is worth it to me.

Having said that, I won't need to use the screw except when getting on the road as the pin-latch should provide good retention while parked. But just not good enough to make me comfortable when driving.

Link to comment
Share on other sites

  • Replies 111
  • Created
  • Last Reply

Top Posters In This Topic

...one manufacturer of spindles for swing arms such as this was emphatic that you must cinch the swing arm down very firmly...
It's probably a consideration for that mfr.'s spindle. But if you use a Ford spindle (like the ones on the front of your truck, or a similar 4WD truck), that consideration becomes irrelevant. A spindle strong enough to hold the ENTIRE TRUCK up is certainly reliable enough to hold a swinging spare DOWN.
...if the clamp is on the right end of the swing arm. And if you place the clamp there the tire would have about 20:1 leverage advantage on it.
Again: irrelevant if you use a stock 4WD hub lock designed to take the torque from the engine (~200 lb-ft) multiplied through the trans (~6:1), t-case (~3:1), & diff. (~4:1); total ~15K lb-ft. The weight of the whole arm & spare assembly should be (far) less than 200 lbs, so its COM would have to be 70' from the pivot (if it were pivoting horizontally, so subject to gravity) to equal the potential load on the hub lock when it's on a real truck.
...thereby closing the triangle.
That's more of a design choice than an engineering consideration. Having a triangular arm in this application does not improve strength or strength-to-weight.
...a metal/metal contact which I'm trying to avoid.
Easy to design out later with a piece of UHMW self-adhesive tape, or a thicker panel screwed on.

But a significant weak point in your design is the catch...

With a round pin (regardless of the hole shape), the whole load essentially rests on a line along the axial surface of the pin, which presses against the stop (the hole in the top of the bumper). That's high-wear, no matter what the material. A vastly-stronger (lower-wear) design is a pawl: a moving prismic shape with a large® surface area in-contact with the stop. Look at the latch on the doors in your house. Just remember that it needs AT LEAST as much wearing surface on its attachment (swingarm) side as on the stop (bumper) side. So imagine a vertical rectangular tube with a rectangular steel bar inside wrapped in plastic low-friction tape. The bottom end of the bar is angled (ramped) so it rides up the top corner of the bumper, and then drops into a rectangular hole, giving a rectangular (vs. linear with the round pin) wear surface. The farther it drops into the bumper, the more vertical slop (bounce) it tolerates, BUT the deeper (fore-aft) it has to be for its ramp surface to have a workable slope. The wider it is, the less wear it will experience, exponentially (~1/4 the wear at double the width) for each material.

The handle for the latch (regardless of shape) does not need to be near the latch itself - it's cheap & easy to add a small operating rod (or flexible sheathed cable) from a conveniently-placed handle down to the latch pin, hidden behind the spare. Common plastic replacement bearings for any vehicle door latch operating rods are cheap & available to reduce wear & noise.

Link to comment
Share on other sites

.... But if you use a Ford spindle (like the ones on the front of your truck, or a similar 4WD truck), that consideration becomes irrelevant....

Again: irrelevant if you use a stock 4WD hub lock designed to take the torque from the engine (~200 lb-ft) multiplied through the trans (~6:1), t-case (~3:1), & diff. (~4:1); total ~15K lb-ft....

Interesting! However I'm thinking there's too much slop in a locking hub to hold the carrier tight enough for even my standards (and Gary sure seems to have a lot higher standards than me on things like this). But as a latch it would be plenty strong.

As to the spindle strength, I wouldn't doubt it either. But it does mean that the end of the bumper would need to be strong enough to take the entire load rather than being able to share it with the latch point.

On your later point about the line contact of the pin latch, I don't think that's a concern in Gary's design because the bolt is what will be holding it while driving.

Link to comment
Share on other sites

.... But if you use a Ford spindle (like the ones on the front of your truck, or a similar 4WD truck), that consideration becomes irrelevant....

Again: irrelevant if you use a stock 4WD hub lock designed to take the torque from the engine (~200 lb-ft) multiplied through the trans (~6:1), t-case (~3:1), & diff. (~4:1); total ~15K lb-ft....

Interesting! However I'm thinking there's too much slop in a locking hub to hold the carrier tight enough for even my standards (and Gary sure seems to have a lot higher standards than me on things like this). But as a latch it would be plenty strong.

As to the spindle strength, I wouldn't doubt it either. But it does mean that the end of the bumper would need to be strong enough to take the entire load rather than being able to share it with the latch point.

On your later point about the line contact of the pin latch, I don't think that's a concern in Gary's design because the bolt is what will be holding it while driving.

Wow, guys! Lots to think about. Let me try to go point by point:

  • Spindle: I'm pretty sure that a Ford spindle will be much too tall. I actually started trying to use a light-duty boat trailer spindle that I happen to have, and it was too tall. And I'll bet that the Ford spindle will be even taller. The issue is where the top of the spindle is with respect to the tail light. The spindle I have in the plans is just tall enough to cover the reflector that is below the backup light, and the trailer spindle would have covered the backup light. So I would expect that a Ford spindle would be into the tail light itself, and I don't want to do that.

    Plus, the trailer and Ford hubs are cast and wouldn't be good to weld to. I consulted my fabricator friend on that one, and he nixed a cast hub. But we even looked at bolting to a cast hub and couldn't make it work. Fortunately, there are at least two companies making spindles specifically for swing arms, and they have steel hubs and are short enough to clear the lights.

    But, I will say that all of this saddens me as I really did want to use Ford parts where I could. :nabble_smiley_cry:

  • Lock: I love the idea of using the hub lock! That's absolutely cool! But, I agree with Bob that the slop would be too much for this application.

  • Triangle: Yes, this is a choice. And I want the triangle closed so there's no give. Obviously there are two ways to design it w/o closing the triangle. One is to omit the vertical piece, and to do that would then focus all of the tire's weight via the lever arm of the upper tube on its weld to the lower arm - not something I want to do as I'm pretty sure it would crack the weld in short order. The other way, by eliminating the upper, angled, arm does away with the jack's mounting point.

  • Metal/Metal: Yes, I'll prevent that with a piece of UHMW between the two parts. I just need to remember to space the stop back to keep the swing arm parallel with the bumper in the closed position when the UHMW is there.

  • Pin Latch: This is the red ball-handled latch that will be used when the truck is stationary. And I agree that there are stronger designs. But, as Bob pointed out, it is not intended for use while driving. In addition, it will be latched into a block of UHMW, and the latch I've selected is probably as strong as the block.

  • Clamp: As shown above, this is the T-handled bolt that will clamp the swing arm down to prevent bouncing as well as ensure it doesn't move rearward. In the illustration above I had a major error as I didn't include the upper support for the T-bolt. So, as drawn, rearward pressure on the swing arm will try to bend the bolt. But with the upper support in, meaning that the t-bolt passes through two pieces of steel which are inches apart, rearward pressure is trying to shear the bolt, which isn't likely to happen given the 1/2" size thereof.

    Having said that, I'm still struggling with that screw as the clamp. And, if it is to be a screw, where should it be? One idea is to make the screw a lot longer so the T is easier to reach. Another is to use some form of a quick-turn fastener so there doesn't have to be a lot of twisting. Or, leave a hex head on it and stash a ratcheting wrench nearby with a magnet. (There are copious tools in the toolbox up front, but that wrench would be handy.)

    Or, use some type of over-center latch to pull the arm down to the bumper. But, I can only put something that is no more than 1/2" high on top of the bumper or the tailgate will hit it. :nabble_anim_confused:

Anyway, please keep those ideas, suggestions, and critiques coming in. Paraphrasing "it takes a village", it takes a forum to design a bumper. :nabble_smiley_wink:

 

Link to comment
Share on other sites

Wow, guys! Lots to think about. Let me try to go point by point:

  • Spindle: I'm pretty sure that a Ford spindle will be much too tall. I actually started trying to use a light-duty boat trailer spindle that I happen to have, and it was too tall. And I'll bet that the Ford spindle will be even taller. The issue is where the top of the spindle is with respect to the tail light. The spindle I have in the plans is just tall enough to cover the reflector that is below the backup light, and the trailer spindle would have covered the backup light. So I would expect that a Ford spindle would be into the tail light itself, and I don't want to do that.

    Plus, the trailer and Ford hubs are cast and wouldn't be good to weld to. I consulted my fabricator friend on that one, and he nixed a cast hub. But we even looked at bolting to a cast hub and couldn't make it work. Fortunately, there are at least two companies making spindles specifically for swing arms, and they have steel hubs and are short enough to clear the lights.

    But, I will say that all of this saddens me as I really did want to use Ford parts where I could. :nabble_smiley_cry:

  • Lock: I love the idea of using the hub lock! That's absolutely cool! But, I agree with Bob that the slop would be too much for this application.

  • Triangle: Yes, this is a choice. And I want the triangle closed so there's no give. Obviously there are two ways to design it w/o closing the triangle. One is to omit the vertical piece, and to do that would then focus all of the tire's weight via the lever arm of the upper tube on its weld to the lower arm - not something I want to do as I'm pretty sure it would crack the weld in short order. The other way, by eliminating the upper, angled, arm does away with the jack's mounting point.

  • Metal/Metal: Yes, I'll prevent that with a piece of UHMW between the two parts. I just need to remember to space the stop back to keep the swing arm parallel with the bumper in the closed position when the UHMW is there.

  • Pin Latch: This is the red ball-handled latch that will be used when the truck is stationary. And I agree that there are stronger designs. But, as Bob pointed out, it is not intended for use while driving. In addition, it will be latched into a block of UHMW, and the latch I've selected is probably as strong as the block.

  • Clamp: As shown above, this is the T-handled bolt that will clamp the swing arm down to prevent bouncing as well as ensure it doesn't move rearward. In the illustration above I had a major error as I didn't include the upper support for the T-bolt. So, as drawn, rearward pressure on the swing arm will try to bend the bolt. But with the upper support in, meaning that the t-bolt passes through two pieces of steel which are inches apart, rearward pressure is trying to shear the bolt, which isn't likely to happen given the 1/2" size thereof.

    Having said that, I'm still struggling with that screw as the clamp. And, if it is to be a screw, where should it be? One idea is to make the screw a lot longer so the T is easier to reach. Another is to use some form of a quick-turn fastener so there doesn't have to be a lot of twisting. Or, leave a hex head on it and stash a ratcheting wrench nearby with a magnet. (There are copious tools in the toolbox up front, but that wrench would be handy.)

    Or, use some type of over-center latch to pull the arm down to the bumper. But, I can only put something that is no more than 1/2" high on top of the bumper or the tailgate will hit it. :nabble_anim_confused:

Anyway, please keep those ideas, suggestions, and critiques coming in. Paraphrasing "it takes a village", it takes a forum to design a bumper. :nabble_smiley_wink:

https://shop.opticsplanet.com/freespirit-recreation-overlander-trailer.html?_iv_code=3H1-TND-TRFY-TROV200&utm_source=google&utm_medium=cpc&utm_campaign=plusbox-beta&gclid=Cj0KCQiAi57gBRDqARIsABhDSMorg3TwrOMr4ajQIf0WGm2qO-gArVNVUkz_fQBgQ7A3Ae0y2r5b0WgaAjn-EALw_wcB

:nabble_smiley_whistling:

Link to comment
Share on other sites

Grumpin - You think I need to go with a trailer instead of a bumper w/a tire carrier? Just leave the spare in the back? :nabble_anim_confused:

Oddly enough, the guy that's going to build the bumper makes off-roading/excursion trailers.

Link to comment
Share on other sites

Grumpin - You think I need to go with a trailer instead of a bumper w/a tire carrier? Just leave the spare in the back? :nabble_anim_confused:

Oddly enough, the guy that's going to build the bumper makes off-roading/excursion trailers.

Here's another link to another early Bronco thread. I haven't looked at it very closely,but it's specifically about custom tire carrier latches. You might find it helpful.

http://classicbroncos.com/forums/showthread.php?t=288715

Link to comment
Share on other sites

The issue is where the top of the spindle is with respect to the tail light.
Not if the spindle is recessed down into the bumper, or if the spindle points down (eliminating the possibility of a hub-lock latch).
...cast and wouldn't be good to weld to.
I'm pretty sure they're forged steel, and are fine for welding. But you wouldn't actually need to use a real hub - just a (weldable) steel tube to fit the bearings into, with splines (which can be VERY sloppy & coarse) for the hub lock to grab.
...the slop would be too much for this application.
Not if you position the arm against the stop, and then adjust the hub lock's angular position to eliminate the slop before welding its splined axle stub to the bumper.
...the upper tube on its weld to the lower arm...
But there's no need for a lower arm - just an angled arm from the hub up to the spare mount, at the angle needed for the jack stowage. No triangle; no bracing; no extra weight/cost/complexity - just an arm to support the spare's & jack's weights.
...I'm pretty sure it would crack the weld in short order.
Only if ALL the welds are going to crack. If you think you (or your welder) can lay down a good bead, then you can lay a good one there.
...it is not intended for use while driving.
I'm still trying to (not-so-)subtly encourage you to use a SINGLE latch that does the whole job.
...into a block of UHMW...
That wouldn't WEAR away, but it would DEFORM far more-rapidly than steel-on-steel. Plastic is too soft for such a concentrated load - it still needs to be spread out over a large flat surface.
Link to comment
Share on other sites

Grumpin - You think I need to go with a trailer instead of a bumper w/a tire carrier? Just leave the spare in the back? :nabble_anim_confused:

Oddly enough, the guy that's going to build the bumper makes off-roading/excursion trailers.

I'm impressed with what you're doing and the planning. That's more tongue in cheek of what I would do, if I could afford it, because I'm not patient enough! Trying to be funny!

And I went back and read the first post to see why you're not using the bed. Makes sense, room for gear.

Link to comment
Share on other sites

Grumpin - You think I need to go with a trailer instead of a bumper w/a tire carrier? Just leave the spare in the back? :nabble_anim_confused:

Oddly enough, the guy that's going to build the bumper makes off-roading/excursion trailers.

I'm impressed with what you're doing and the planning. That's more tongue in cheek of what I would do, if I could afford it, because I'm not patient enough! Trying to be funny!

And I went back and read the first post to see why you're not using the bed. Makes sense, room for gear.

Bob: Thanks for the link. Those guys were going through many of the thought processes I/we've been going through - and coming to many of the same conclusions.

And, they were using/thinking of the same clamps I've been looking at, three of which are shown below. The top one below is from Smittybilt. I know 'cause I held one in my hands yesterday at 4WD Parts when I took Janey in so she could shop for a few gifts for me. It is part #76856-05. But, it doesn't really appear as something the sell on their website, so I'll have to call them - if I can figure out how to use it.

But, I haven't figured out how to use any of those. The limitations are significant, and include that I don't dare put anything more than 1/2" high on top of the bumper or the tailgate may hit it, and the big spare tire prevents placing something in the center. But, it would be easy if the lower arm went all the way across. :nabble_anim_confused:

81_5.jpg.95088425001d1eeed70e627e5656bfbf.jpg154_0708_04_z2bjeep_tire_carrier_shootout_fab_fours2blatch.jpg.e3478759fa553012ea1dcdb41bedf17a.jpgR2125-full.jpg.a33106120d24c2e1d3aa5b729b50206d.jpg

Steve: I haven't gotten a mind's eye view of how the spindle could be used upside down, nor easily recessed into the bumper. But that's sorta moot as even if the hubs aren't cast, and you may be correct, they'd take a hole bunch of machining to get down to the diameter that would fit - if that is even possible given the size of the bearings. And to make a hub is more machining than I want to do - especially since I'm hoping to make this something that can be built commercially and/or by others.

So I'm not going to use a Ford spindle. Instead I'll be using one of the commercially-available spindles meant for this purpose as they'll fit w/o obscuring the tail light and don't require a lot of modification. None, in fact.

As for the swing arm, I'm going to use a closed triangle. I want a stop/rest on the far side of the swing arm that takes the load off of the spindle and ensures there are no rattles, and that is much easier to do if the arm has a component that is a fraction of an inch above the bumper.

And, I'm going to have two latches - one that is easily used while "in camp", and one for traveling that is very positive that ensures the whole contraption cannot move in any direction. Just what that positive latch will be is what I'm struggling with, and that's where I'd like to have help.

Grumin: A trailer would be easier in many ways, but it will also be more expensive, cut down on the already-dismal MPG, and would have to be dropped before heading out on many of the trails. But, it is something that I did consider before embarking on this quest. :nabble_smiley_wink:

Link to comment
Share on other sites


×
×
  • Create New...