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Fabricating And Installing A Custom Rear Bumper - Bump ’N’ GrindFrom the January, 2012 issue of Rod & Custom By Kev Elliott
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Over the years I’ve owned the Purple Pig ’49 Chevy, especially when it was on the road, I’ve always wanted to do something about the “plain” rear bumper. I felt it needed something a little more elaborate to add extra styling, as well as a little more chrome, to the rearend of the car. A few months ago, I stumbled across a mid-’50s Oldsmobile in my local late-model junkyard. After a few hours with wrenches and a hammer and chisel, the grille was mine for a paltry $18. I figured it’d make a neat addition to the ’49, with the exhausts exiting through the oval sections. The oval sections of the junkyard-sourced... The oval sections of the junkyard-sourced Olds grille line up with my tailpipes, but with it mocked in place it extends too far from the body. Time to trim it down! To make it more of a feature, as well as an attempt to slim it down a little, I decided to recess the rear panel and form it around the Olds grille. (That’s why the centersection of the panel and floor I installed last month weren’t fully welded, and why the latch mount was only tack-welded in place.) Once I had the center of what would become my new bumper mounted, I could tackle the ends of the bumper. My Miller Spectrum 375 X-Treme plasma cutter proved its worth in trimming the old Chevy bumper end sections to fit up against the Olds grille. Using the plasma took minutes instead of something that would have taken much longer to do neatly using a grinder and cut-off wheel, especially as I had to sneak up on the final cut, trimming small sections away until I achieved the fit and look I was aiming for. Holding a Sharpie against... Holding a Sharpie against a pencil and dragging the latter across the rear body panel gave me a cut line to trim the bumper. I took the opportunity to move the bumper ends closer to the quarter-panels, and also welded up the old mounting holes. With new side mounts welded to the backside of the bumper ends, all I have to do now is fabricate a couple of mounts to replace the old bumper brackets, between the quarters and the chassis. You’ll notice I mounted the Olds grille directly to the rear crossmember, rather than on brackets that would give a little. I did this for two reasons: mainly so the bumper wouldn’t move around and scratch the paint on the edges of the recessed rear body panel, but also, as the car is so low, and the bumper is its lowest point, if it ever gets hit, I have a feeling the bodywork will take the brunt of an accident, not the bumper, so there’s no need for it to be fitted on sprung steel brackets! Now I’m one step closer to completing all the sheetmetal welding, and rapidly approaching the body prep and paint stage. Finally!  I used my Miller Spectrum...  I used my Miller Spectrum 375 X-Treme plasma cutter to trim the bumper. This 30-amp machine will cut up to 3/8-inch mild steel, yet is fully portable. It does require an outside air supply though, which was capably handled by a Harbor Freight compressor.  The 375 X-Treme can be connected...  The 375 X-Treme can be connected to either 115V or 230V supplies simply by switching these plugs, the machine sensing which voltage is being supplied. The 230 V is required for cutting heavier-gauge steel.  The plasma cutter made light...  The plasma cutter made light work of trimming the bumper. I used a short length of 1x1-inch box section as a guide to follow the Sharpie mark, rather than freehand cutting.  With the excess cut away,...  With the excess cut away, the “bumper” was placed back against the rear body panel so I could mark where the sheetmetal needed to be trimmed.  Note the cut line marked on...  Note the cut line marked on the sheetmetal, though before I did this I marked a centerline on the body panel and the bumper.  Before I cut any bodywork...  Before I cut any bodywork away, I mocked up the complete bumper assembly using a rough-cut section of the bumper end piece. Though not fully trimmed or in the correct position, it gave me an idea of whether or not I liked what I was working toward before any further cutting took place.  The lower section of the rear...  The lower section of the rear body panel was cut away and clamped in place higher up, meaning I could now mock up the bumper again, with the centersection in its final location. I used racer tape to fill in the upper end section.  Moving the bumper into the...  Moving the bumper into the rear panel area meant I had to also remove the rear section of trunk floor. Here’s most of the panel I installed last month, now cut away again!  Before I mounted the center...  Before I mounted the center of the bumper I ensured it was level side-to-side ...  … as well as checking it was...  … as well as checking it was vertical. The ’49 is on jackstands, with the rear higher than the front, so I used an angle finder to measure the angle from horizontal of the door bottoms, then set the bumper up so the vertical faces of the oval sections were at the same 3-degree angle. This means they’ll be vertical when the car is on the ground.  Years ago I replaced the rear...  Years ago I replaced the rear crossmember with a 2x3x1/8-inch length of box section, with the intention of fitting a tow hitch. This crossmember is plenty strong enough to support the bumper, so I fabbed these brackets using the plasma cutter, and added a gusset for strength. The brackets support the Olds piece using its original mounting holes. The blue towel is protecting the ceramic coating on the exhaust tips.  With the center of the bumper...  With the center of the bumper now solidly mounted, I could trim the rear body panel for a butt-weld, while maintaining an even gap between the body and the bumper. I reused the lower piece with its return lip, and used magnets to hold it in place while tack-welding.  The EMS trunk floor section...  The EMS trunk floor section was then reused to close the open section of trunk floor, once I’d trimmed the step off it, which previously dropped down to meet the return lip on the rear panel. The top of the bumper recess is now flush with the floor.  After tack-welding the rear...  After tack-welding the rear panel in place, and before I removed the bumper center again, I marked the curve I needed to trim at each end on the stepped section of floor, removed it with a cutoff wheel and dressed it with a rotary file in a die grinder.  The curved end pieces of the...  The curved end pieces of the recess were formed in this shrinker/stretcher from Summit Racing, using the stretcher jaws.  With the bumper section bolted...  With the bumper section bolted in place once again, the curvature could be perfectly matched before the new section was tack-welded in place. I took advantage of the gap in the panel for access to seam-weld the new section to the stepped floor.  Another small filler section...  Another small filler section closed off the panel, again using a magnet to align the sections while tacking. All these pieces were butt-welded.  Not the prettiest right now,...  Not the prettiest right now, and with a little extra planning I wouldn’t have needed to add the small filler pieces above the curved sections, but it’s all back in one piece. Now to break out the grinder.  With the welds dressed, I...  With the welds dressed, I cut the ends from the old gravel pan, as I still wasn’t entirely sure what I was going to do at the ends of the bumper.  The ’49 had a three-piece...  The ’49 had a three-piece rear bumper, so to free the end sections the rivets had to be ground down and then punched out.  With the stock bumper end...  With the stock bumper end trimmed to fit the Olds piece, and moved closer to the body, it looked like this when mocked in place.  I cut a section of 2x1-inch...  I cut a section of 2x1-inch box section C-channel, drilled it, and welded a 3/8-inch nut on the rear, then welded the assembly to the rear of the bumper end to form a new mount.  A Unibit was used to drill...  A Unibit was used to drill the rear quarter to accept the bolt.  Here’s what the mount looks...  Here’s what the mount looks like from the inside. I’ll fabricate a new bumper bracket to go from here to the chassis, so the ends of the bumper aren’t simply bolted to the sheetmetal.  My Millermatic 211 handled...  My Millermatic 211 handled welding the sheetmetal as well as the 1/8-inch bumper material, both on 115 V, though as with the plasma cutter, the 211 can be used on 115 or 230 V, simply by switching the plug. Welding steel over 3/16-inch requires 230 V.  Looking across the car you...  Looking across the car you can see how the top edge of the bumper ends align with the outer edge of the centersection. Note, I also welded the bumper boltholes closed, though since we showed you how to do this last month, I’ve skipped that step.  Now the bumper ends are closer...  Now the bumper ends are closer to the bodywork, I’ll shave the top edge to match the curvature of the quarter-panel.  Though this looks fine in...  Though this looks fine in bare steel, I can’t decide whether the remaining gravel pan sections should be painted or chromed. Or should I section the bumper ends and roll the top over into a plate where the gravel pan is, making the whole assembly one piece? That’d mean lowering the reveal on the quarters, but might look best. Hmm …
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