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Adding Seatbelts to Cargo Area - Help Wanted for Planning!

Wire Fox

Well-known member
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Location
Indianapolis, Indiana
I'm still not running, but I do want to add seatbelts to the rear as an important safety upgrade for when I am. I plan to make continued use of the fold-down troop seats whenever practical. I'm reading plenty of information showing that side-facing seats will never have the same level of protection as a forward- or rear-facing seat, due to the excessive whiplash forces; however, I want my potential passengers to have at least some element of safety for at least a low-speed collision or a quick maneuver to at least prevents them from being thrown from their seat.

I don't see any practical way to get them into a three-point seatbelt, so I'm limiting this to being a basic retention 2-point seatbelt. My initial reading (based off of DIY RV camper types) shows that additional seatbelts are typically bolted through the floor or directly into structural framework, which makes sense. One number I heard thrown out for hardware sizing was 7/16", which also sounds reasonable (and I would use in grade 8). I think that it would probably be best to just put in about two sets of seatbelts on each side of the HMMWV, since they could be bolted through the fender. I'd like to copy the design used for the upper support bracket of a rear seat 3-point belt, as I trust AM General's engineering a bit more than my own.

So, what I'm looking for... does anybody have any dimensions and information about that 3-point bracket? I'd like to know how thick it is and the width of the U-channel that they used to prevent the seatbelts from tearing through the sheet metal. As well, I'd like to hear any suggestions if anybody might have another way to do this. I just think that this is a pretty cool way to retain seating for an extra 4 people with a reasonable amount of safety, without sacrificing the cargo capabilities that I want to keep. I most often only will have 1 other person and they will enjoy the passenger high-back with 3-point belt, but I don't want to have to completely deny having more than 1 passenger.

HMMWV cargo seatbelt diagram.jpg
 
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Wire Fox

Well-known member
1,252
161
63
Location
Indianapolis, Indiana
Doing a search awhile back for a seat belt bolt for a M1008 it came up that factory bolts are grade 12.
Are you sure that wasn't a metric grade 12.9? I'm not aware of any SAE/ASTM spec grade higher than 8. It's worth noting that metric grade 12.9 and SAE grade 8 are roughly the same. Thanks.
 

riderdan

Member
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18
Location
Central Kansas
Are you talking about the gold-colored pieces in this picture?
setbelt.jpeg

<edited> Looks like I don't have them any more. My truck didn't have the rear belts when I bought it but the reinforcement pieces were already under the fender.

Can you find the paper templates for installing them? Those would have the measurements.
 
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Wire Fox

Well-known member
1,252
161
63
Location
Indianapolis, Indiana
You guys are right, it is those gold ones in that picture. Good thinking on the template, I should be able to find that in a TM somewhere and will help me figure out dimensions and confirm fastener sizes. Juanprado, I'll keep that in mind, as that's a good price. I'm not ready to jump yet, especially since that bracket might not work until I'm sure I've got the right dimensions figured out.
 
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