Hitch ball through crossmember?... Maybe..

[sixbennetts]

Would this be dangerous? There's already holes there, 2 of them bigger than the hitch ball shaft. Would one more hole hurt?

Thinking about using a hitch ball as the front attachment for a 2500lbs camper, as part of a 3 point mount.

Question 2. Where exactly on the frame is the best place to attach the other 2 parts of a 3 point mount? I thought I read that the best place was just in front of the rear spring hangers.

Thanks!

ps. Thanks for the frame drawing, found it here.

 

[SkiFreak]

I am pretty sure that when the engineers at Fuso designed the FG chassis they never planned on the cross members taking the loads you are proposing.
Would I do this on my truck... NO.

You should also be mindful that installing a 3 point mounting system on a stepped chassis requires some serious attention to engineering detail, as you have twisting forces working on different planes.

 

[John M.]

I'm no engineer, but my instincts are that is not a good plan.

How about converting a 5th wheel saddle from a pickup truck to span the width and tie in to the rails in a way that spreads the load?

 

[sixbennetts]

So, I should sort of 'duplicate' that crossmember either in front of or behind the existing crossmember, making sure that the weight is on top of the frame rails, right? I guess that makes sense, seeing as there's less frame flex in that area compared to the back frame. I like the idea of a 5th wheel saddle from a pick up truck.

Attachment to the frame via U bolts and plates, of course. And yes, mounted high enough to allow the box to tilt side-to-side.

By using a hitch ball with a long shank, I'll be able to adjust the height a little bit up or down, but how high should it be above the frame so it doesn't hit? 3" or 4" do it? How high is everyone's box above the frame in the front?

And what's the best spot for rear 2 points, A, B, C, or D? Or somewhere in between?

 

[Aussie Iron]

Why try to reinvent the wheel. Three point mounts have proven to be a problem to many that have gone that way whereas spring mounts have given (next to) no failures that I have heard of.

Dan.

 

[SkiFreak]

Why try to reinvent the wheel.

I agree wholeheartedly with Dan on this one.

As much as 3 point mounts can work well, they are a lot more complicated, especially on a stepped chassis, where the flexing can be somewhat weird.
Spring mounts are relatively simple and will weigh less. If you design the subframe to also be supported over the length of the chassis, that should also eliminate any point loading.
Each to their own, I guess...

 

[SkiFreak]

I should probably ask... are you planning on having a passthru in your truck?

If you are, having the single pivot at the front may result in a lot of freedom of movement, which may affect the ability to keep the connecting sock in place.
If you're dead set on using a 3 point mount, you may want to consider having the single pivot at the rear, which I believe is the most common configuration anyway.

 

[yabanja]

I am a fan of the three point mount but feel it is important to build a siginificant subframe in between in order to strengthen the noodle like stock chassis for the reasons that SkiFreak mentioned above. If you must go this route- I would build as large a plate as possible out of 3/8" steel and bolt it to the crossmember with the hitch ball sandwiching it.

Allan

 

[sixbennetts]

2500lbs camper, so not a lot of weight. Plus, I'll be removing most of the trailer tongue, (shortening it), moving propane tanks to the truck frame, maybe even the fresh/gray/black water tanks, too.

I'm going to replace the trailer axle with something much more substantial, (box tube inside box tube), and use the trailer suspension as the other 2 points. With shocks, of course.


Camper will be a 16' off-road style with a heavier frame and fiberglass construction. I'll determine whether or not to go with springs over or under the axle, depending on how the hitch ball mount comes out on the front.

Oh, and no pass-through. Small campers are abundant up here in the Adirondacks, so if one breaks, it'll be easy enough to find another one. And we're not rock crawlers up here in the northeast. We're glorified dirt-roaders! Plus, we'll be using this on Sandy Neck and Race Point beaches for camping.

Pretty tame terrain.

 

[sixbennetts]

Yup, considering a long shank hitch ball with either a spring or urethane bushing under it.

Maybe even suspending the hitch ball between two springs across the frame rails. We'll see.

 

[dan85]

a guy close to me has done something similiar on his 2004 NPS300. Jump on the isuzu NPS series 4x4 facebook group and ask there he will pop up and send you a bunch of picture.

 

[sixbennetts]

I'm a visual thinker, so here's some thoughts. Hitch ball will have a urethane washer under it. Haven't decided whether ball plate will be bolted to the two crossmembers or welded, (they will be steel, now aluminum as shown). Urethane pads between plate and frame rails. Haven't decided which way the U bolts will go, probably nuts up so they'll be easy to tighten if it gets loose. Obviously, the trailer hitch itself will be shortened considerably to get the front of the camper as close to the cab as possible. If I measure correctly, I *might even get a couple spare tires between the camper and truck cab.

About the trailer's stock axle. Obviously, I'll replace it with something stronger, or maybe sleeve it with heavy wall tubing. But it will be square or flat rectangle in profile, not round. I'm also considering a simple underslung truss under the axle, depending on how wide the spacing is between the trailer springs compared to the truck frame width.

Where did we land on the A, B, C, or D on the first image, re: axle placement on the truck frame? I'm doing my reading here, and I thought I read the rear 2 points on a single-point-forward 3 point subframe should be just in front of the rear spring hangers. Sound right? Obviously, I *might have to move the trailer's spring shackles to meet that point.

 

[sixbennetts]

a guy close to me has done something similiar on his 2004 NPS300. Jump on the isuzu NPS series 4x4 facebook group and ask there he will pop up and send you a bunch of picture.

This one? Just joined, who do I look for?

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[sixbennetts]

Seller on ebay can do all kinds of urethane blocks/pads. No connection to seller.

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Probably source heavy U bolts at our local junkyard. They have tons of old trucks.

 

[dan85]

This one? Just joined, who do I look for?

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Yeah I saw your post in there pop up. the guy with the towball on the crossmember is Arnold who I think has already posted?