MudChucker... your friends solution of 4x4 tubular risers is interesting.
CrazyCooter... Thank you for the idea about the MorRyde pin box, which has led me to their pin box identification and ordering page, which has provided a great deal of information.
Long Pin Boxes are between 25" and 29" from king pin to second row of bolts, with most of them being 29".
Medium Pin Boxes are between 16" and 23" from king pin to second row of bolts,
with the average being 18".
Short Pin Boxes are too varied and short enough not to bother trying to average.
The take away here is that as I suspected, some pin boxes are indeed too long, and would crash against the insides of my service boxes if my hitch plate were not high enough, even while those boxes are no higher than the sides of a pickup box. 49/2 = 24.5, so a 25" to 29" long pin box would crash! Ouch!
A medium pin box, which is up to about 23", would theoretically clear, depending on the geometry of the trailer mounted structure that the removable portion bolts to. I believe this is structure that Big Bird 2 is referring to cutting a 45 degree corner off of the back side of, in the post he made while I was typing this one. The average medium pin box of 18" would clear.
A short pin box would laterally clear without issue, but then the vertical clearance becomes a problem, as pinboxes in general seem to adjust down and out, not just down.
Down and out brings up an entirely different clearance issue... the diagonal clearance between king pin and left or right tail light at the corners of the truck bed. One of the benefits of an outward adjustment is the ability to lengthen tailgate to FW riser (aka drop wall) clearance.
Being that my truck is a cab chassis with a 40 gallon aft axle fuel tank, the distance between rear drive axle centerline and rear bumper is a little bit longer than that of a pick up truck with only a midship fuel tank. Specifically, if the king pin were postioned dead center at 0" from drive axle centerline, then I require 72" clearance to the rear corners of the bed, which themselves are 56" from the ground.
Having a medium or short pin box could reduce the FW riser to TV tailgate corner clearance.
This is quite frustrating, how the overhangs of fivers are so short. With a 60" cab to axle distance, I'm not worried about crashing the back window. I'm worried about swing clearance on the side boxes, and simultaneously, swing clearance as the bumper and tail light corners sweep in front of the fiver dropwall.
I have the standard 64" clearance between rails so I am OK, you have a tough situation. Maybe you could invent the first left/right slider?
fred
Big Toe,
Please note from the pic, that the pin box only moves vertically between bolt locations. It does not move down and out as you think. Also, why wouldn't an auto slider hitch with a medium length pin box work? The auto slider will give you extra clearance at the corners of the service bed while turning and the medium length pin box will not hit the sides of the service bed.
You won't find a slider hitch with the low profile you need. This is the same problem I had. But most service bodies do not have a structural crossmember above the axle or near it. So, I cut a section of the diamond tread plate floor out and recessed it to accommodate the height of a standard profile hitch.
* This post was
edited 07/29/12 04:24pm by Dayle1 *
Larry Day
Texas Baptist Men-Retiree Builders since '01
'03 GMC 2500HD D/A EC SB, Jordan controller, custom RKI bed/hitch, TF 45gal tank, grey Speedliner
'11 CrossRoads Cruiser CF32MK loaded Rig Photos
Mine is 27.5" from the center of the king pin to the edge of the pin box. It angles up from there. An eight foot bed does not really require an extended pin box so it could be switched but short box trucks are going to want to have the extended pin box.
Thank you for pointing out the vertical only adjustment of the pin box Fred posted.
There are however, some pin boxes that I have seen that are called "Telescoping". I noticed them back when I was taking measurements at an RV lot that was a couple hours drive away (where I ignorantly did not think to measure horizontal length) but I did not know at the time that they were termed "Telescoping" until I read the MorRyde hitch identification document.
Apparently the telescoping type of pin boxes can telescope "down and out" at either 34 degree, 45 degree, or 72 degree pitches. I don't remember the brand of fiver that the RV lot I visited sold, but that manufacturer seemed to use a lot of the telescoping variety.
This is PRECISELY why I put the question to all of you, because of skewed perception that limited experience can yield. That particular RV dealer may not have a representative sample of typical fivers that have pin boxes that do not telescope, but only adjust up and down soley. So I'm glad you pointed out this distinction.
I looked at your photos, but see more of your trailer than your truck. I'd love to see more of your truck. I'll keep poking around there.
I'm quite curious if there were any stiffeners welded to the underside of the diamond plate portion you cut out. I'm also curious how you managed drainage from water filling the bed in rainstorms with your cut out, the platform underneath, and how concentrations of water pouring down directly above the pinion bearing of the axle were redirected.
Maybe installing your hitch behind the axle with the shorter pin box could be your answer for both issues?
Mine is located 3" behind the axle as with my longer wheelbase, it only took about 90lb off the front axle which we needed anyway since I was a few 100lb over.
I AM NOT A MECHANICAL ENGINEER. Pardon if I look at the extending the pin issue from another angle... seems to me you're asking for trouble from a torque perspective. When you're on the road, especially a bumpy road, if the length of the pin is extended, it can't help but increase the torque on the frame welds from the pin box back to the 5th wheel overhang to the main body of the trailer.
NOT a M.E. so pardon my comment if totally invalid.
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....Who cares.I have my TH AND my toys 
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