If you have a cracked or broken gauge bezel in your 1967 Chevy Camaro, or a cracked doorsill plate in your '85 IROC-Z, this article applies to you. I just wanted to let you know that you can fix broken plastic instead of rummaging through wrecking yards or parts catalogs to find replacement parts.
I learned these tricks as a mechanic at GM. Our customers didn't always want to buy new parts, so we were able to save them a lot of money with repair. This repair doesn't hold up on high-stress pieces but works great on most ABS and plastic interior parts. I put this fix to the test on my '68 Camaro gauge bezel. The corner was snapped off, but luckily I had both parts. The fix has lasted 16 years of daily driving and abuse. Before you start, just know that this bonding patch method is ugly and requires building up about an 1/8-inch of material, so I suggest patching only the backside of the panel. The outward facing, visible surface can be repaired with a little glue, filler, primer, and paint.
To do this, you'll need easily obtainable products such as super glue, fiberglass mat, sandpaper, and some baking soda. The baking soda gives the super glue some extra meat to help make the repair more solid. Zip Kicker is the key ingredient, and will take a little more effort to obtain. It's sold in most hobby shops as a bottled liquid to drip on to repairs or in pump-spray can form. Zip Kicker is a super glue accelerant mostly used by hobbyists building and repairing radio-controlled vehicles and planes. A few drops make the super glue set up instantly. I highly suggest performing a test-repair on two pieces of junk plastic before trying it out on your prized parts. That way you'll know what to expect and will understand the bond ahead of time. You can also practice not gluing your fingers together.
Be sure to keep the visible side of the repaired area as neat as possible. The backside of the panel is where you do all the dirty work. Carefully glue the two parts of the crack with super glue. Scuff the backside around the repair with some 80-grit sandpaper. You'll have to make the surface very rough so the repair will have a good surface on which to bond. I usually use a razor knife to create a crosshatch pattern in the surface of the plastic, just for good measure.
This job will create nasty fumes, so do this in a well-ventilated area and take precautions necessary to protect your skin, eyes, and lungs.
Cut a small piece of fiberglass mat and place it over the roughed-up area. I've seen guys get away without using fiberglass mat, but I wouldn't try it for a long-term repair. Pour super glue on to the fiberglass mat and the surrounding area. If the fiberglass mat moves, reposition it with a twig or toothpick, not your finger. Before it dries, sprinkle a little baking soda into the glue and then spray the area with a little spritz of Zip Kicker. With some popping and cracking, and a little puff of smoke, the pieces are then bonded back together.
Now that the crack is fixed, you can leave the non-visible repaired area alone and work on getting the visible side of the panel looking good. I'm not trying to hide the ugly side of the repair; people won't see it, and grinding the fiberglass mat will weaken the repair.
You can usually purchase paints that match the proper interior colors for your Camaro from Classic Industries, Year One, or other restoration catalog sources. With some filler and some sanding, you can refinish the visible side of the panel and paint it the correct color.