Frame extension/Bumper mount

[Fenderfour]

I've got an old Japanese firetruck with a step bumper on the back. There is a bunch of junk welded to the frame to support the bumper and I want to clean it up and add a more "normal" bumper.



additionally, the frame box section is an odd size, probably metric.

I also need to extend the frame 12" to the frame to accommodate a camper.

I'm thinking about welding a plate to the end of the existing frame like so:



And then adding the 12+ extension to the bumper, and a mating plate on the end of the extension. There will be recovery eyes on the bumper in line with the frame rails.



What do y'all think?

 

[ExpoMike]

In my opinion, the two angle iron pieces are not going to do anything and are a waste. What you really need is to sleeve the box frame back at least 12" from the end of the frame. Ideally box tubing would be best but you could use C channel. You might need to fabricate these items (box tube or C channel). You might find some box tubing that could slide over the outside of the frame rails. It would also be easier to weld your "box tube" if you sleeve it on the outside of the frame, instead of trying to sleeve it inside.

 

[Fenderfour]

In my opinion, the two angle iron pieces are not going to do anything and are a waste. What you really need is to sleeve the box frame back at least 12" from the end of the frame. Ideally box tubing would be best but you could use C channel. You might need to fabricate these items (box tube or C channel). You might find some box tubing that could slide over the outside of the frame rails. It would also be easier to weld your "box tube" if you sleeve it on the outside of the frame, instead of trying to sleeve it inside.

Thanks for the reply.

Yeah, the angle isn't doing squat. It's a leftover from the firetruck step bumper. They welded the ******** out of it, all around the periphery, looks like a fat arc weld. I'm trying to not disturb the weld since it is so intrusive. Lots of cutting/grinding/patching. A sleeve requires me to remove it, but you are the second person who recommends a sleeve, so i guess I'll have a go at it.

 

[Fenderfour]

Adding length to accommodate a LONGER camper seems to be a hot spot of frame failures likely because the internet will always give the answer you want.

Japanese stuff tends to be engineered for the task .... PERIOD... unlike North American stuff which tends or TENDED to be over bilt with less regard for overall weight.

Me, I'd be inclined to stick to the original dimensions of that Japanese Fire Truck..... guaranteed the manufacturer never intended it to be modified. For me the challenge would be to build without adding weight or length.

Thanks for the input.

I mean, in generalities, sure. The frame of the base truck is fully boxed. It's beefier than almost any domestic I've seen. From my research, it's a Land Cruiser 7x series frame with a DOKA van cab on top. I'm pretty sure it's rated 1.25 tons, even though it's smaller than my '21 Subaru outback. Different versions of this same truck were rated up to 1.75 tons, it comes from an era when Toyota only had one frame for it's "light" trucks. Later, they split the model into Dyna, HiAce, and ToyoAce, roughly aligning to use/loading

Pic for reference


The total finished length of the camper will be less than the step bumper currently is. The step bumper is mostly diamondplate pop-riveted to the bed with that z-shaped angle support welded to the frame. That's why there is angle iron welded to the frame in the sketches in my first post. The base truck bed is from a 7X series land cruiser.

In total, the step bumper is ~18" longer than the frame. I want to remove the crappy angle iron and add a more robust, shorter, and straight extension.

 

[Ozarker]

I think I'd just trim off the step, build a frame from the bottom at the rear, 45' up toward the back, put plate down at the back of the bed, full width, basically a shelf bracket.

Are you trying to put a slide in camper on that?

If you're building the camper on the back I'd just cut that step off, the departure angle isn't great even after losing the step.

 

[Fenderfour]

I think I'd just trim off the step, build a frame from the bottom at the rear, 45' up toward the back, put plate down at the back of the bed, full width, basically a shelf bracket.

Are you trying to put a slide in camper on that?

If you're building the camper on the back I'd just cut that step off, the departure angle isn't great even after losing the step.

I'm planning a custom build from the frame up, not a slide-in. Not sure how I will mount the box to the frame, as I still need to test frame twist.

 

[Ozarker]

I'm planning a custom build from the frame up, not a slide-in. Not sure how I will mount the box to the frame, as I still need to test frame twist.

Then if you're talking the bed off, building a box on the frame, just cut that stuff off from the back of the original frame.

Your box can go back further than the frame, like this;



Side entrance will give you a better floor plan as well.

 

[rruff]

I also need to extend the frame 12" to the frame to accommodate a camper

In your figure the 12" extension is just for the bumper... or do you intend to mount the camper to that section?

 

[Fenderfour]

In your figure the 12" extension is just for the bumper... or do you intend to mount the camper to that section?

Hope to use it to mount the camper. I also want strong recovery points and a solid base to mount a bike rack back there.


Sent from my iPhone using Tapatalk

 

[rruff]

Hope to use it to mount the camper. I also want strong recovery points and a solid base to mount a bike rack back there.

Are there recovery points you can use on the existing frame, and can you mount the camper to the existing frame? My camper extends ~20" past the frame and the bumper a couple more. The bumper is on the light side and the only load is the step for getting in and out. Recover points are on the beefy hitch which is in the stock location and bolts to the frame.

Bikes are not heavy. If you have a side entrance you could mount the bikes to the camper itself, which might be easier.

You say that the frame is heavy duty, but just be aware that a large load with a CG behind the rear axle can be problematic. If it's fully boxed I very much doubt you'd have an issue with solid attachment.

What sort of camper are you planning?

 

[Fenderfour]

Are there recovery points you can use on the existing frame, and can you mount the camper to the existing frame? My camper extends ~20" past the frame and the bumper a couple more. The bumper is on the light side and the only load is the step for getting in and out. Recover points are on the beefy hitch which is in the stock location and bolts to the frame.

Bikes are not heavy. If you have a side entrance you could mount the bikes to the camper itself, which might be easier.

You say that the frame is heavy duty, but just be aware that a large load with a CG behind the rear axle can be problematic. If it's fully boxed I very much doubt you'd have an issue with solid attachment.

What sort of camper are you planning?

There are no good recovery points on the frame. I think the end was simply lopped off to add the step bumper. I'm currently fabbing a simple beefy bumper with receiver and it will connect with the frame extension to add recovery points in line with the frame.

Bikes are "Light", but my Mountain bike is ~35 lbs, my SO's is ~30, and the rack is 50, so it's a fair amount of weight cantilevered off the back.

I am planning a side entrance pop-up camper. The width of the door is the primary reason I need to extend the frame. I can't fit a door in front of the rear wheels, so I'm adding it aft of the rear wheels. I also want to stay under 7'6", as I'm hoping to ship this rig over seas at some point.

I am very aware of the issues loading aft of the rear wheels. Having the entry back there requires me to keep it open. All of the heavy stuff (batteries, water, fuel, etc...) will be in the forward section.

Here's a sketch that I use to plan the CAD model:



I want to keep it as small as possible. Just a bit of living space and a bed.

I guess if I went with a rear entry floor plan I could make the whole thing shorter, which isn't a terrible idea. I could improve the departure angle. I was hoping to store a spare back there, but it might be worth it.

I'm pretty sure the camper will not have any fancy articulated mounts. As I said before, it's a landcruiser 7X series frame. I've done some preliminary flew tests and seen no movement, which makes sense since the rear wheels are so close to the cab. I need to load it a bit more and get the wheels higher before I'm sure to mount it directly. Earthroamer does a baby RV on the landcruiser frame without an articulated mount, so maybe it will work?

Someone is going to pop in here and ask why I'm not using SIP Panels. It's because I don't need the insulation, and I don't want a 2"+ thick wall. I can weld an aluminum frame, skin it with DiBond and save a lot of weight and cost.

 

[rruff]

Love your rig!... it's just enough space to be comfortable, and be easy to maneuver and capable of going anywhere.

Your rear overhang isn't bad at all, less than I expected.

I hate putting nice bikes outside. I don't know if you've looked into it, but you could maybe angle the rear of your camper and put them at the same spot, only indoors....?

Pretty certain you'd have no need of articulating mounts. If you are attaching your bed to the cab you may want to check if the cab has rubber or poly mounts and do something similar with the camper.

If you wanted some insulation and like it cheap, DIY panels using 1" XPS would fit the bill. Wet layup... and you could embed 1" square fiberglass tubes in the wall for supports and hard points. A little insulation can help a decent amount in sunny-hot, and cold conditions. Just a thought; what you are planning will work also. Were you planning on using 5000 series tubing or 6061?

 

[Fenderfour]

Thanks. I'm definitely going for functional, not luxurious.

I've been carrying the bikes on the outside of my subaru for years. I think they will be ok. I will probably get a cover for them when I'm out in the truck.

I was planning to add 1" xps on the inside, I can route channels in the XPS to run wire/hose as needed. The XPS should fill the void between frame members. I will add a quilted insulative material like Thinsulate to the inside to cover the XPS and the frame members.

Will look into poly mounts. Might replace the cab mounts as well so it's all new and working properly.

Planning to use 6061. The extra strength is worth the cost, I think.

Thanks for all the input/feedback rruff.

 

[rruff]

I thought people used 5000 series alloy when welding because it isn't heat treated, but I see that the welded zone gets weak regardless. 6061-T6 square tubing is readily available, but 5000 series is rare.

 

[Fenderfour]

There is a lot of colloquial knowledge when it comes to materials. Welding a heat-treated material doesn't ruin it. At most, it returns it to an annealed state, but even that is unlikely since the annealing process for aluminum requires holding the material at a critical temperature for hours. For 6061, you need to hold 775 degrees for 2-3 hours.

"Yield" is the point at which the material will bend. "KSI" is a measurement of force = 1,000 PSI (Pounds per Square Inch)
5052-O (annealed, most common) yield = 13ksi.
6061-T6 yield = 35 ksi
6061-O (annealed) yield = 12 ksi

Worst case, the welded areas of 6061-T6 are -almost- as strong as the 5052. We know that a few seconds of welding doesn't anneal the 6061, that it will be in-between 12 ksi and 35 ksi. Folks have done the research, and the typical strength of welded 6061-t6 is around 22ksi (yield).

I thought people used 5000 series alloy when welding because it isn't heat treated, but I see that the welded zone gets weak regardless. 6061-T6 square tubing is readily available, but 5000 series is rare.