Our ’60 Corvette’s last drive was down a dragstrip in 1973. Disassembling a barn-find Corvette brings surprises, both good and bad. On one hand, you may find some items in better than expected condition, while seemingly minor parts are in complete disrepair.
The C1 Corvette was never famous for being weather tight, even when they were new, so it came as little surprise that virtually every bolt inside the car was rusted solid, leading us to believe the car may have sat outside for some period of time. Body mounts, seatbelt brackets, convertible top brace bolts, and the seat mounting bolts were all completely rusted, well beyond the power of any penetrating oil. A prior owner had snapped off most of the bolts and in the process several of the tiny nut plates had been spun out of the floorpan, too. After removing the seat frames from the car, we tackled all the mounting points in the cockpit.
One look at the small pieces of riveted sheetmetal holding the 5/16-18 nuts to the bottom of the floor and we knew there must be a better way. Now, I’m no engineer but I do know that spreading the mounting force over an area 1 1/2 by 7/8 inches is pretty minimal. The plan was to not only replace the mounting points but make them stronger in the process.
The end result was seat mounts much stronger and safer than what originally came in the car. In fact, we liked it so much we decided to tackle the seatbelt attachment points and body mounts as well.
1. After removing the seat cushions you’ll find the seat frames. The seat frame is bolted to small nut plates riveted to the fiberglass floor at the factory. The bad news is that many times these bolts are rusted beyond removal.
2. After we removed the seat frame we unbolted the seat sliders from the frame to illustrate how the seats are held in place. Five out of the six bolts on each seat either snapped off from rust or the riveted nut plate came loose from the body, it is time for improved mounts.
3. This is the right front seat mount on the passenger side. Notice how a previous owner had snapped off the nuts. The mounting plate is sandwiched in a fiberglass channel so we must cut the top layer of the floor to remove the rusted nut plates.
4. After marking the cut lines on the floor, a die grinder and cutoff wheel made quick work of cutting the top layer of fiberglass. Take care not to penetrate the lower layer of fiberglass. Removing the top layer exposed two very rusty and very small nut plates.
5. The factory nut plates are pretty wimpy, barely 1 1/2 inches. They were very rusted so it was difficult to tell if the original metal was 14- or 16-gauge, but either way, we were determined to do better.
6. We spent a little time completely cleaning out the seat mounting channel in preparation for our new seat mounting plate.
7. Before we put the nut plate in position for the final time we decided to strengthen the bottom of the cavity. There was a hole that went all the way through the bottom panel that allowed moisture to migrate into the area so we cut a piece of fiberglass weave and glassed it to the lower floor panel.
8. We cut a piece of 2x9x1/8-inch cold roll steel for a mounting plate. After locating the holes we TIG welded, using our Miller Syncro-Wave 200, two 5/16-18 nuts to the backside of the plate.
9. It always pays to run a tap through the nuts after welding to ensure good, clean threads. As you can see, this mount incorporates both boltholes and is substantially stronger than the small factory nut plates.
10. The new nut plate extends 2 inches under the uncut floor in each direction. We decided to use fiberglass to hold the plate in position in the channel.
11. Before we could fiberglass the nut plate into the channel we gave two 5/16-18 bolts a liberal coating of anti-seize and threaded them into the nut plate. This prevents fiberglass resin from filling the threads on the nut plate.
12. After the fiberglass resin and mat had cured we removed the bolts from the mounting plates. As you can see, this will be a much stronger mounting plate than the factory offering.
13. With the nut plate glassed in place, we put the top layer of the floor back in place in preparation for more fiberglass work. Some sanding was required to ensure the top was perfectly flush.
14. Once again, the bolts were threaded into the nut plates prior to laying down two layers of fiberglass mat and resin. Satisfied that we had repaired and improved the front mounts we turned our attention to the rear mounts.
15. The rear seat mounts simply mount through a single floor panel with the factory nut plates riveted in place. We removed the nut plates, leaving us with four holes. Note the outboard mounts (left) have only one bolthole. Our replacement mount will make this a two-bolt mount.