It's not a question of "if" but "when." The factory-installed rubber body mounts (pads or cushions, depending on the year) on any Solid-Axle, Mid-Year, or Shark that has seen even moderate road time over the years will need replacing. The original components deteriorate from exposure to the elements, dirt, grime, grease, and oil. The old rubber will get hard and brittle, crack, and break apart. When that happens, the creaks and groans factor increases exponentially-and on '63-82s, where biscuit-like cushions are used, a collapsed cushion could, in extreme cases, cause the body to droop or sag enough to cause more than the normal stress cracking of the fiberglass body panels.
Mid-Years and Sharks, which employ very similar body-to-frame mounting arrangements on their essentially identical frame (with the major exception of the ends of the frames, for the body designs and various bumper mounting systems), use eight sets (two pieces per set, an upper and a lower) of cushions, four per side, to affix the body shell to the frame. Working from back to front, the first set (No. 4) is accessible from the fenderwell, just behind the rear tire. The second set (No. 3) is accessed through a small screw-on panel in the forward portion of the rear fenderwell. The third and fourth (Nos. 2 and 1) sets are both in the cowl area, and there is no direct body-to-frame support or attachment forward of the firewall-the entire nose section, including the hood and pop-up headlight assemblies, is suspended by where it's glued in place around the cowl.
The rear-most sets are the only ones that are even marginally visible. To check the condition of one of the rear sets, you really need to remove the tire and wheel, but with the rim and rubber out of the way, it (the cushion set) is hanging right out there in plain sight. And you can figure that if it shows cracks and splits or other signs of deterioration (and it will), it's time to change all eight of 'em. You may as well do the job right.
We're not talking about a high dollar expenditure here. A stock-replacement-style rubber single cushion set sells for around $18. If you buy a complete kit, the eight sets of cushions, and new body mount bolts, nuts, washers, and shims, plus a pair of new body mount access covers (they go, one per side, in the forward portion of the rear wheel well), the total expenditure will be under $200. Our point is, don't scrimp on it. All of the components are readily available. For those who are planning on keeping their Shark for more than a few years and are aiming for an NCRS/Bloomington Gold sort of restoration, polyurethane bushing sets are available-for a lower price than the rubber repops-and the poly pieces should last for the life of the car.
Unless your Shark is from one of the dry southwest (desert) regions of the U.S., the original nuts and bolts will probably be thoroughly rusted in place and together, so plan on soaking all of them regularly, starting a week or so before the work is to be done, with some sort of rust dissolving/penetrating material or lubricant (WD-40, RustBuster, etc.). It'll make the job less difficult and less unpleasant. You can make the chore easier if you remove the seats, carpeting, carpet underlayment, left and right kick panels, and the ducting from behind the kick panels. If the carpet in the Shark is worn, or you've been thinking about adding a heat barrier kit to hold the interior temperature down to a light roast, this is the perfect time to do so.
Our subject car is an L82/four-speed '77 owned by Scott Norseth. This particular Corvette spent its first few years in New York before being relocated to the dryer climes of the left coast and sunny Southern California. That brief exposure to salted roads was just enough to cause corrosion on the body mounting hardware but, fortunately, not enough to cause a rusted frame, which is not an uncommon malady on vintage snowbelt Vettes.