what did you do to beef up that rear bumper for tow point duty?
Honestly, nothing. I positioned my D-links *just* inside of each frame rail for optimum load transferal to the frame, anytime I pull from them 99% of the load goes straight to one frame rail, the rest has to transfer sideways through the bumper to the other frame rail, I feel this is defiantly better than if I had put them outside the frame rails, and a tiny bit better than if I had put them in-line with the frame rails. This way the other frame rail at least knows that there is a load, I have seen a truck where they were pulling on 1 frame rail and they ended up sliding it forward. If you were to look at that frame from above or below it is now a parallelogram instead of a rectangle. I'm relying on the bumper to act as a cross member as well, a job which I think it is up to. Other than that I made sure the bolts were in good condition and made sure my welds had good penetration.
I think sooner then later its gonna end up pulling your bumper off.
Thank you for your concern, but I don't think I will pull my
rear bumper off, if I'm stuck bad enough that I feel there is a danger of pulling it off I will tie into the frame for that pull. I know I will never pull the
front bumper off. If someone wants to suggest that I am in danger of shearing six 1/2" grade 8 bolts with a 4400 lbs truck then.... IDK, but I sincerely doubt that will happen.
*IF* anything ever comes apart on the rear bumper I have
chosen my weakest link to be the bumper-to-frame union, which there is 2 of. This is so when I reach the point of something failing the first thing that will happen is one side of the bumper will come off the truck. My experience has been that things like this will bend and not all four bolts will fail at the same instant. There will at least be a moment of warning (and a noise?) before the whole pulling assembly (winch?towrope?) comes undone. This gives you a second to either let off with your pulling device, and/OR duck and cover, hehe.
For the rear bumper to come undone two 1/2" bolts have to shear. I know that metal strengths come into play here but to have a quick look at it...
Two 1/2" bolts have a shear area of 0.1963 sqr inches, (remember there is two perside, =4)
ONE 5/16" winch cable has a tensile area of 0.0767 sqr inches.
So two bolts have more than double the area of metal that has to fail compared to the cable that I do 90% of my recovery work with.
So even if the frame-to-bumper bolts don't prove to be the failing part, I think the bumper itself is next in line. Again, it has been my experience that things like this yield before they completely fail, giving the people (that pay attention anyways) some warning. There is the heavy drawbar section (1/4" plate?) that mounts to the frame rails. If this is the part that fails it will bend before it comes apart, thus letting me know. I sized the D-links bigger than the frame-to-bumper bolts because I don't want to have D-link's or clevis's (or parts of either) becoming bullets when winching.
*IF* I manage to mangle/ruin this bumper, I will be forced to build something on-par with my front bumper, then there will be no more trouble.
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