What Are the Frame Tabs Called That a 5th Wheel Pin Box Mount to?

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Question:

Hi, I have my small fifth wheel at a local welding shop to get a quote. A previous owner cobbled together a goose neck ranch style hitch to the fifthwheel. In doing so, he butchered the ttrailer framing tabs that stick down into where the pin box or goose box would bolt up to. First question, what are those frame tabs called. Ive seen Reese installation manual call them wing sets. Id like to know their correct name for sure. 2nd - are there different standards or only one standard reguarding wing set hole placement. I seem to be finding evidence there are straight down, or angle forward mounts wing sets and differing number of holes per side. My current butchered setup has only two holes per side, wallowing out. I measured 9.5inch between hole centerlines, 12inch between wings. Are wing sets normally welded on or bolted to the trailer frame? If the shop cant make me a new setup that prevents bucking, I might decide to put the money into a Reese hitch. Your thoughts?

asked by: David P

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Expert Reply:

Hey David, great questions! I'll answer them in the same order you asked them:

1 - There isn't an official name for those brackets that I know of. They are part of the trailer frame so I guess technically they are pin box frame brackets, but another common term for them is "wing brackets" since they look like wings without the pin box installed.

2 - There are different mounting hole patterns like you referenced and, consequently, there are different pin box sizes and weight ratings. Attached is a link to a helpful article about these measurements, but from what you gave me it looks like you have a mounting bolt pattern for a Fabex 560 pin box. This is an older pin box style and the only replacement we have for that is the Shocker 5th Wheel to Gooseneck Pinbox # SHK55MR, but this still has the gooseneck coupler so it wouldn't work if you're wanting to move to a standard 5th wheel hitch setup.

I recommend reaching out to the manufacturer of your 5th wheel hitch to verify which pin box number initially came with your RV and then you can use our article to have the weld shop install new mounting brackets if those are needed. Aside from that, it sounds like you're looking at a custom fabrication job so I recommend having a shop do the work that is familiar with this type of situation and is able to take into account all of the stress that comes with 5th wheel towing.

expert reply by: Jon G

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Dave P.

4/25/2024

Thanks Jon for an excellent reply and a great attached article. To date I have advice from two local welding and fabrication shops. Each has recommended I purchase a new goose box and I could hire them to repair or fabricate new frame brackets to accomodate the new goose box. I will need help deciding which goose box I should buy, based on what can be done with my existing butchered brackets, either removed and new frame brackets put in, or new material welded to the existing bracket stubs. Over the next few days I will be reviewing what I can to help me make this decission, and I would love to receive advice and assistance from you and others at etrailer. I can send photos and measurements and describe my needs. First of all, I want to use a gooseneck hitch coupling, not a fifthwheel coupler. My truck has the goose ball directly over the axle. My truck has an 8' bed and the current configuration required a goose coupler with an 8" offset. I do not want to bring the trailer closer to the truck so I suspect I'll need a longer goose box than what is on there, to accomodate for the task being done now by the 8" offset. I will reread the article you sent and come up with the measurements I am targeting, but I may need your assistance along with it. I am currently at the critical height minimum of trailer to truck rail distance. It is 7-8" (8" at furthest forward height, and 7 at furthest rear contact height. Theoretically I could change tires and possibly wheels to give slightly more, but it is an old trailer and while I am building it for cool use, I will need to control spending somewhere. I already had a local shop build me a 6" subframe to raise it, and you might see from my past orders it has some fancy electrical jacks and stabilizers on it. So, that's kind of an opening. I'm leaning toward a Gen-Y dampened hitch, but am open to any ideas for safety and minimizing bucking, and reasonable pricing. My current butchered brackets are 12.5" wide, so I asume that means I'm looking for a goose box that is 12.5" wide. But, if plate metal is welded to the bracket stubs so as to provide more mounting holes, that distance would narrow, as the material would need to be on the inside, rather than the outside where support fins are welded. And if my box becomes longer as I described, as exists with the current coupler 8" offset, in a tight turn it puts the goose box within swing distance of the bed rails, so it cannot be too tall at that point (frame brackets point). Thank Jon. What do you think?

Reply

David

4/26/2024

Hi Jon. Now I'm leaning more toward a Reese Goose-box, 16K (my trailer is small and light-weight, only 7500 lbs GVWR). I like the cushioning features on it better than the Gen-Y. But, upon measuring, I have the long pin/goose box. That is to say my butchered and cobbled together current pin/goose box is homemade, using a ranch goose-ball coupler, with an 8" offset. That setup does position the trailer to my truck appropriately. Measuring from the existing holes in the butchered trailer frame brackets, I'd like 36" from rear hole to goose ball, and 26.5 from front hole to goose ball. That is NOT measuring a diagnal, but indeed is a horizontal distance. That's due to the small trailer dimensions, the 8' truck bed and a desire to avoid an off-set ball, if at all possible. The vertical rise is also somewhat tall. From the bottom of the coupler flare (which is 3" below the ball top) up to the centerline of the in-use mounting holes, is 26". That is because the mounting holes are basically at the same level as the bottom of the house overhang, plus maybe 2" in stub height. I realize 36" is long, and 26" is tall, but that is based on my existing holes, which in essence are unusable due to the previous owner's modifications. What remains of the frame brackets could be used as stubs to weld to. I could then have a welding shop build new frame tabs, matching whatever configuration I need. Say for instance, match and make new frame brackets that are to spec for a Lippert 1621 frame bracket (or buy new ones if they are available), a bracket that the Reese 16K goose-box is designed to fit. For example, my existing brackets are spaced 12.5" wide. A Lippert 1621 is 12" wide. The remaining .5" could be taken up by welding in 1/4" steel to the inside surfaces of my frame bracket stubs and redrilled for Lippert 1621 hole spacing. These fabricated brackets could also be shaped and angled, so as to cant forward, perhaps as much as the 10" or so from existing rear hole, to the newly drilled rear holes, in an effort to further reduce the existing 36" length down to something closer to 26", as the hitch itself might require. Canting forward on a bracket angle would also help to remove the bracket from a bed-rail collision, angled forward, instead of straight down. Upon a tight turn, the angled portion would be closest to the bed-rail, not an otherwise tall bracket rear edge. These are some of my current thoughts. I wanted to kind of bring you up to speed. At this time, no answers or solutions are needed from you. But if you are interested, I could send pictures to help you visualize the current crazy setup. Just tell me how you'd like to receive them. Thank you!

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Jon G.

4/29/2024

@David Thanks for all of the insight! The Reese Goose Box # RP85FR would get you the adapter style you're wanting and provides multiple mounting holes for various setups, but it doesn't hit the length or height requirements you're wanting. Since you're going to have a welding shop help you with the installation I highly recommend consulting with them on this as they would be better suited to make decisions on a fabrication job like this. I would also make sure the welding place you're dealing with has done this type of work before. Welding metal together is one thing, but welding pieces together for the purpose of 5th wheel towing is another.

Reply

Dave

4/29/2024

@JonG Thanks Jon, good advice. I have been learning a lot lately and will next take this matter to the welding shop. Today I am leaning toward keeping the current setup, because it is the correct length and height, and improving on it. It consists of an Anderson Ranch Hitch with the coupler being an 8" offset, and a 12" coupler tube, as opposed to the Ranch Hitch parts I've been seeing with an 8" long coupler tube. The pin box itself is a homemade unit that has it's personal strengths and weaknesses. It has been working, but due to only 2 bolts per side, has been moving up and down slightly. I have redesigned it and added to it's reinforcement areas by installing cardboard cutouts into those areas (for professional shop/welder imagining and advice), drilled two new holes each side, to allow a 1.5" pin box drop, intend to drill and install two additional holes/bolts on each side (for a total of 4 each side), not in a straight line but in a modified Vee pattern to allow for increased strength of geometry. That can all be done on the remaining portions of the factory frame brackets. When all is said an done, I believe this will work well. No cushioned pin box, but rather the Ranch Hitch engineered for 24K GTWR / 6K tongue weight - while mine is a small light trailer, 7500 lbs GTWR and 1650 lbs tongue weight. I would not attempt such customization on a heavier fifthwheel trailer, but for this little unit, I believe I'm on the right path. Thanks for the shop professionals advice you offer. And for you help bantering this about.

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What Are the Frame Tabs Called That a 5th Wheel Pin Box Mount to?

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