In our last installment, we covered the engine, drivetrain, and brakes. we are busy working on the many remaining tasks for our project, but we thought we would cover one aspect of the interior that has drawn quite a bit of interest lately. There will be more on other interior features in a later installment.
If you like the style, comfort, and the ability of newer seats to grace your bottom in the manner to which it has now become accustomed, you may be considering upgrading/changing your seats. While there are aftermarket seats available, many folks prefer to use as many Corvette components as possible when modifying their cars.
Installing C5 seats is becoming a popular way to achieve those goals, but getting them to fit and mount correctly can be an issue. Having gone through that recently, we thought we would share the approach we took to install them in a '63 coupe. We found some C5 seats on eBay, and the ones we have seen range from nearly new and perfect to those that will require reupholstering. The ones we found were a little worn, but since we planned to reupholster them anyway, there was no need to pay the price for perfect seats.
We chose to eliminate the power seat motors in order to lower the seats, eliminate the weight and wiring involved, and simplify the installation. To remove the power mechanism requires removing the seat bottom upholstery and foam in order to get at the four mounting bolts. At least that's what we did since we couldn't figure out a way to get at the bolts easily as they go into the power unit from the top of the seat frame. It isn't difficult at all, and you can put things back the way they were by reinstalling the hog rings at the rear of the seat and retightening the drawstring used to secure the seat-bottom upholstery.
For the installation, the main issues that need to be addressed are: seat height, seat rake, mounting, adjustability, and upholstery color match.
Seat Height: Installing C5 seats with their power adjusters in place can raise the height enough that you can hit your head on the ceiling of a coupe. The mechanism also weighs about 20 pounds each so you can save 40 pounds by eliminating them. If you want to retain the power feature, another approach is cutting and lowering the floors, but we didn't want to go that route.
On a convertible, you might find the seat headrests taller than you like, although we don't believe they are much taller than a midyear with the headrest option once the power seat assembly has been removed. If that is an issue for you, the seatbacks could be cut down somewhat to a height you prefer. If so, you will also likely have to move the seatback lock to a lower position. In a coupe, we didn't find height to be an issue.
Seat Rake: We found it helpful to raise the front of the seats so the angle of the seat bottom will help keep us in place and avoid the feeling of sliding forward.
Mounting: There are two areas to address here: Manual seat tracks can be fitted to the C5 seat frames, and the seat tracks need to be securely mounted to the floor.
Adjustability: Even without the power motors, the C5 seats retain their seatback adjustment. Most folks will also want to be able to adjust the forward and rearward position.
Seat Upholstery: You may be able to find seats which are fine; we've seen many on eBay. If you're lucky you might even find them in the right color to match your interior. If not, there are stock upholstery kits from a variety of sources, or you could go the custom route.
Seat Height: Replacing the power units with manual seat tracks from a '75-'77 Corvette will lower the seats enough to allow sufficient head room. These are usually readily available, and we found them on eBay. Other years may also work.
Seat Rake: we found that making four "risers" gives the right angle to make the seat bottom comfortable and hold you in place. These are positioned at the four C3 seat track mounting points for each seat. The front risers we used are 1 & 1/4-inches tall and the rears are only 1/4-inch tall. Depending on your height and personal preference, you may want to experiment to achieve the rake that feels best to you. All four are angled at 4 degrees to allow for the angle of the seat tracks. We used 1-inch-diameter solid aluminum for the risers. Each riser has a 3/8-inch hole in the center for the mounting bolts, which are 3/8-inch x 6 Allen (socket) head bolts. The front bolts are 2-inches long, and the rears are 1 inch in length.
The seat risers also provide another function by allowing the clearance needed for the mechanical adjuster mechanism arm on the seat track, as well as clearance for the cables used for the seatback adjustment.
Mounting: There are two areas requiring mounting: the manual seat tracks to the seat frames and the seat tracks to the car floor. The former is accomplished using the risers and bolts mentioned previously. The locations of the new holes you need to drill and tap are shown in the accompanying diagram. Basically, you need to drill and tap two new holes at the front underside of the seat frames, which are 1 & 9/16-inch in from the outer edge of the seat frame and spaced 14 & 3/4 inches from the rear mounting holes. The rear mounting holes use two of the holes now occupied by the innermost rivets that are at the rear of the seat frame. The easiest way to remove the rivets is to use the appropriate size punch and drive the inner portion of the rivet inward. Then, drill the rivet center with a 1/4-inch drill bit to remove some of the rivet head and cut the head of the rivet off using a sharp chisel. The inner portion of the rivet will go inside the seat framerail, but those pieces can be extracted through the center hole in the crossbrace. We used a vacuum to suction them out. Then we drilled the hole with a 5/16-inch drill bit and tapped the holes for the 3/8-inch x 16 socket bolts.
Once we had the seat tracks mounted, we installed the seats in the car to get the position we wanted, making sure we had the seat tracks fully to the rearward position and marked the holes we will need to drill through the floor. Midyears have a steel plate riveted underneath to accept the stock seat mounting bolts, but we found the holes didn't line up, and we preferred to increase the thickness of the mounts. We made three new plates for each seat from quarter-inch-thick steel, which were bonded to the underside of the floor. A single front plate is used for both front seat track bolts and measures 17-inches long by 1 & 1/4-inches wide. Two smaller plates were used for the rear seat track bolts to better fit the contour of the floor which measures 3 & 1/2-inches square.
Adjustability: With the seats and seat tracks in their proper position, we now have full fore and aft travel. We also have the seatback adjustment to get the seatback at a comfortable angle. Since we have already set the seat rake, we now have comfortable and supportive seats that also fit and look great in our midyear.
Seat Upholstery: In our case, the seats we found were worn, but we needed to change to match the colors we are using anyway. We purchased nine full leather hides of two tones of grey to achieve a more modern look. But we wanted to retain the same basic '63 patterns and style for the seats and door panels. We also had our logo digitized and embroidered on the seat headrests.
As usual, there are many ways to go about any project, and you may find your own method for this installation. After looking at a variety of methods, we found this approach gave us the height, comfort, and adjustability we wanted.
Although we have test fitted the seats, we aren't at the point where the interior is ready for our final seat installation. In the meantime, we hope the accompanying photos and descriptions are helpful if you are considering installing C5 seats in your midyear.
As we write this, we have 90-plus items remaining on our latest punch list, so we've a long ways to go on our project. We hope you've enjoyed what you've seen thus far.