Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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Rick, welcome to the Forum!
Which avenue it will take to repair your '72 endura core support, will depend on how extensive the rust out is.
The mildest rust outs only effect the body bushing holes in the lower U channel of the original core support. This is a very typical problem on '68-72 Pontiac Abody & '69-72 GP coresupports. Over the last 3 decades, have disassembled well over four hundred Pontiac A & GP's of this vintage. Even 25 years ago, most Southern '68-72 Pontiac donor core supports showed some rot out in the bushing holes. On a few instances, I've replaced the entire u channel with one out of a donor that the top plate had suffered irreparable damage. On quite a few others, I've cut out a rectangular area in the rusted core support channel with either my small airsaw or my Ryobi (Dremel) cutoff tool & wheels. Next cut out a replacement piece out of scrap 18 or 16 gauge metal & then buttwelded the replacement piece in with the MIG. The first core support I repaired this way, a friend actually used a stick welder, just took more grinding. Installed correctly, & carefully buttwelded with the MIG, after careful grinding, the repair is invisible. Once the replacement piece is welded in I'll use a hole saw to properly relocate the hole. Will then come in with a die grinder bit, & elongate each of these recreated bushing holes so each hole is slightly oval shaped. This is how the holes were originally, to allow for some side to side adjustment.
When rust outs have been worse, have repaired several original coresupports that were blown out bad below the battery tray area of the drivers side upright. These were in local's driver type LeMans & GTO's & I was able to repair them, as had parts coresupports out of cars that had been popped down the front passenger side, wrinkling the top plate & rendering the coresupport good for nothing but parts pieces.
The worst condition rotted out original coresupports require more intensive action. Have been through this process, now, coming up on a dozen times. This last method of repair is by replacing the entire upright or damaged top plate...
Mentioned this years ago on PY boards... on one of my HO cars, the '71 T-37 Coupe, the previous owner from the late '80's gave up on finding a nice FRP (fiberglas) header panel & butchered the leading edge of the original '71 core support with an airsaw so a '72 LeMans (Metal) header panel could be attached. To reinstall the correct '71 FRP header panel back on the T's coresupport, I ended up drilling out all the spotwelds of the notched top of the original rustfree coresupport. Next I did the same on a '71 V8 coresupport that had a nice top, but was blown out bad down by the battery tray area. When doing this, I use a small 1/16" -3/32" diam drill bit to predrill the center of each spot weld. Next, I come back with a spring loaded hole saw style spotweld cutter. By carefully taking the donor top off, drilling from the bottom side, this will only leave the small pilot holes in the top of the core support plate. This yields the desired top plate with the small round plugs (nubbs) that have to be ground off on the underneath side of the top plate. The same will be the case with the flange areas on the coresupport upright. After all these nub like plugs are carefully ground off with the angle grinder, the top plate can be carefully positioned & carefully plug welded to the core support upright from the bottom side. After epoxy primer & a light coat of high build, I'll apply a little amt of spotputty to each small hole then lightly sand each area, before another coat of epoxy primer. This "top swap" technique can also be used when taking any of the three cosmetically different '71 or '72 "GTO" top plates off rusty core supports & welding them to donor uprights. As time allows, have several '70 GTO, '71 endura, & '72 endura coresupports that I will be restoring. Over the years I've resisted throwing away coresupport donor uprights & even recently, out in yards, have actually pulled a few more coresupports just to get the top plates off them.
Hope this helps, best to you with your '72!