Bumper Building, Day 2

Sunday morning I returned to the Eastern Shore for day two of building my rear bumper for the Scout. While this was my second day, technically it was Brian’s third or fourth, because he had worked hard to get his ready for our trip to Hatteras back in September. Here’s a picture of what his looks like, completed:

Now, a little history: We built the design around a hinge we found online, which was rated for 3000 pounds and built for hanging fence doors. With that in mind, we decided to mount the hinge to the face of the bumper and have the swingarm come off the front, vs. a pole hinge on top. The reason for this was to keep the pivot of the arm closer to the middle of the bumper instead of the top of the far corner, and to allow for more clearance between a lowered tailgate and the top of the bumper.

What wound up happening was that there is a lot more vertical play in the hinge than we’d anticipated—it looks like it was designed to carry a heavy vertical load in tandem with one or more identical hinges, but never to deal with shear loads by itself. When it’s pulled free from the receiver, it immediately droops by about 1.5″ under the weight of itself, a Hi-Lift, and spare tire. This is, as you might imagine, not optimal. We decided to move forward with the design and materials we have, and if we come up with a better solution, grind it off and replace it.

On the other side, we cut down a section of 2.5″ box tube and added a trailer pin to close the swingarm.

To mount to the body, there are two standoffs of 2.5″ box mounted to plate, using the four holes from the OEM standoffs. We also welded angle support to the backside of the frame to beef up the mount point.

Provisions for a Hi-Lift are on the swingarm; Brian drilled bolt holes and welded two supports to the underside for the jack to rest on. I’m going to swap ends with my mount so that the foot of the Hi-Lift is on the hinge side.

So. Yesterday’s labor started with two angle grinders and a lot of noise. With three people working, we had all outside surfaces clean, deburred, and straight in about an hour.

It was during the grinding portion that I discovered the main tube is tuned to a high A#, according to the app on my iPhone.

The first things we did were to tack in the endcaps on the main tube, then put the Hi-Lift notches in place. We’re having a pro lay in the full welds; this is all just for placement and transport.

We moved on to the top swingarm, measuring and correcting for clean 90° angles. Once we’d straightened it out, it got tacked into place. Then we measured and tacked in the side supports to brace everything together.

Once the arms were in place, we measured (again) for the diameter of the spare tire (mine is 32″, Brian’s is a 31″) and added a few inches for clearance, then welded a mounting plate to the standoff, tacked that to the vertical arm, and added a 45° gusset directly below.

After taking a break, we cleaned up a little bit and got things ready for mockup. First, my OEM bumper had to come off, which took some PBBlaster and air tools. Then, we clamped the OEM standoffs to ours and drilled out the holes. Next, we mounted the new standoffs temporarily and then lifted the new bumper into place, supported by a single 2×4″. After careful measurement, marking with a sharpie, location of a fire extinguisher, and a few Hail Marys, we tacked the standoffs to the back of the bumper tube.

Looks good!

By this time, we were pretty tired, I was facing an hour and a half ride home over the bridge, and anything else we wanted to do would take some serious consideration. The hinge is the big question; we’re thinking about alternatives to the mechanical problem, or changes in the geometry (angling the hinge slightly upward to account for droop).

And, on the plus side: the manifold replacement surgery is holding strong, quiet, and smooth. It no longer sounds like a thundering herd of doom, and the cabin doesn’t stink of exhaust anymore.