I have 2 rear quarter panels in my possession, both supposed to be originals,what is the Original colour from GM supposed to be: grey or black? This would be for REplacements, and were they both availabe from GM, and maybe they changed suppliers? On an original car, what colour would the back of the panels be?
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Re: 72 rr quarter panels
Casper,
Original replacement fiberglass panels from GM can, depending on when originally purchased, could be both black and gray. Replacement panels prior to 1973 were black, later and current panels are gray. This date is not exact; phase-in of new manufacturing methods may have occurred over years.
More importantly, current replacements are SMC (sheet molded compound) rather than the original polyester based GRP. Polyester based bonding adhesive does not work for SMC; you have to use an epoxy based adhesive like Fusor. I would definitely use the "black" panel.
Examine the back surface of the panels for date codes; if they are GM replacements, I would expect them to be dated and have a stamped part number. The black, well, more like a dark charcoal gray, panel is original for '72. On original cars, the back side of panels exposed to the elements is usually "dirt" colored; they sandblasted the panels during assembly to enhance bond strength, and the rough surface will have in-grained dirt that cannot, in my experience, be removed.
Chuck Sangerhausen
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