C5 Corvette seats are great. They offer excellent lateral support, tilt forward and backward with enough range to make almost any driver comfortable and have all the different inflatable support areas to keep the car comfortable for long-range road trips—like the 1,000-mile weekend we just did in our Sebring Silver 1998 coupe, La Bala. Unfortunately, and you knew this was coming, they also have two common mechanical problems, not counting routine wear-and-tear of the leather and foam. The way to figure out which of the problems you have is to ask yourself if your seat slides or rocks.
The first problem, sliding, results from the chintzy bushings in the drive gear that moves your seat forward and backward. They tend to pummel themselves into shards and mix with the drive gear grease to create a peanut-butter like slurry, leaving a quarter-inch or so of fore-and-aft play in the seat that you notice every time you stop. More accurately, every time the car stops because you usually stop moving forward about a second after the car does.
The fix consists of replacing those bushings inside their housing, which is bolted to the floor side of the seat track and through which the drive gear passes. The repair kits usually come with four new bushings, enough to do one seat. While it’s not a job for a careless person, it’s not too complicated and can be done in about an hour or so.
The second, rocking, problem is considerably more involved. The seat mechanism that raises and lowers the seat does so by rotating a pair of cross-shafts mounted to the seat track (one in front, one in the rear). Each cross-shaft has a pair of brackets on it that bolt to the seat frame and are mounted on an eccentric to the shaft, so that rotating the cross-shafts raises or lowers the brackets and therefore the seats. Needless to say, the cross-shafts themselves are subject to an inordinate amount of strain, and the cast-aluminum flanges into which the cross-shafts mount are a known weak spot. When they break, repairing the damage involves removing the entire seat track assembly from the seat frame, so it’s major surgery.
Because the simpler (and likely more common) job is the sliding one, we’ll start with that, and then move on to the more complex one. Corvette Central provided two kits for this article: one that will fix the sliding problem for one complete seat and another that will replace one broken flange to fix the rocking problem. If both flanges are broken on a given seat, you’ll need two kits. If only one side is broken you’ll need to know which side to order for since there a left and a right side kit.
The first order of business is seat removal. Move the seat backward, exposing the front seat track cover, and raise the seat as high as it will go, front and rear. Remove the seat track cover by first prying its small head forward, which will then let you pull the whole thing out of the seat track cover. If it’s too stubborn for your fingers, (gently) use a screwdriver. With the retainer out, slide the seat track cover forward off its mounting tab on the seat base, exposing the 15mm nuts that hold the seats to its four studs. Once those are off, moving the seat forward will expose the rear mounting studs. With all four nuts removed, disconnect the electrical connector mounted to the side of the seat track just inside the door sill. The multi-pin connector is attached to the track on the same small grey plastic bracket we’re used to seeing everywhere else on the C5, so slide it off to remove it. The seat can now be lifted carefully out of the car, something you’ll find easier if you remove the Targa or convertible top first.
Once the seats are out, start the track disassembly by putting the seat upside down on your work bench, making sure you first pad the work surface so it won’t damage the seat.
It’s important to know that the drive gears (the two long threaded rods that move the seat forward and backward on its tracks) are threaded in opposite directions from one another, so there is a definite right and left. The caged nut housings on both must be located in exactly the same place on the drive gear prior to reassembly, for obvious reasons. You can use tape to mark where the housings were on each shaft and carefully screw them back in the same place. Instead, we screwed one of the drive gear retaining bolts through both drive gear mount brackets, connecting both gears together so we could make sure the housings were perfectly aligned. We also kept the two T25 Torx bolts screwed into the right side housing so we always knew which side was which. Vette
This deceptively simple repair kit was supplied by Corvette Central and will fix the sliding problem. It comes with four new shims (enough to do one seat) as well as the two Torx wrenches to disassemble the seat track.
This is the seat side of the electrical connection you’ll need to undo to get the seat out. Notice the light grey mounting bracket located just behind the plug: the connector on the car side of the harness mounts to it. The wire retainer (the thin steel piece to which this plug is connected) needs to come off the seat track by gently prying one end out of the hole into which its tab fits, then lifting it off.
Removing the wire retainer will expose these two T25 Torx bolts that hold the caged nut housing in place on the floor side of the seat track. The drive gear (a long threaded rod mounted on the seat side of the track assembly) passes through the nut captured by the housing: when the gear turns, it moves the seat either forward or backward against the resistance of the housing.
This T40 Torx bolt passes through the flange we’ll be replacing to fix the rocking problem and into the bracket that secures the rear end of the drive gear. Removing it while the seat is still installed on the track can be difficult, and we resorted to slipping a pipe over the end of the wrench for leverage.
With the rear mounting bolt removed, the drive gear assembly can be removed from the rear of the seat track assembly. Note the caged nut housing on the left side of the drive gear and the drive gear mounting bracket on the right, at the end of the drive gear. The housing attaches to the floor side track, while the bracket bolts to the seat side.
This transmission cable connects the drive gear (into which it is still seated) with the transmission that turns it (from which it has been removed), which is on the left at the front of the seat track. It slips into matching square recesses on both the transmission and the drive gear and it can fall out easily. During reassembly make sure it is fully seated on both ends prior to screwing in the drive gear mounting bolt. If you can see the square part on either end of the transmission cable it’s probably not in far enough.
The source of the problem: note the black caged nut in its grey housing as well as the empty space on either side of the nut. That’s where the bushings should be. Pulverized fragments of the bushings are a small part of the gunk all over the assembly.
After removing the caged nut from the drive gear, carefully clean out all of its recesses before pressing in the new bushings, using a screwdriver to pry them into place, if necessary. Note that the nut has a “peak,” which must be kept toward the open side of the housing. The left- and right-side drive gears (and their matching caged nuts) are threaded in opposite directions from one another, so keep each on its correct side. Clean and lightly grease the gears before reassembly and make sure the housings are threaded to the same point on each drive gear so the seat tracks will line up.
Now for the rocking problem. On the rear underside of the seat, locate the drawstring that pulls the seat cover tight and untie it, then work the seat cover loose all around the base of the seat. Once it’s loose, either set the seat in its usual upright position or lay it on its side, so long as you can access the seat adjuster handle.
Remove the seat adjuster handle by using a small screwdriver to push in the metal clip visible in this slot while pulling the handle outward to free it from its splined shaft. Once the handle is off, remove the seat adjuster switch panel by unscrewing the screw located directly about the handle and the longer one at the front of the panel. Be cautious; these are 20-year-old plastic and may be fragile. Ask us how we know.
Unplug and remove the switch. We found it was easier to unplug the switch if we first took it out of the switch panel, which requires only gently prying back a couple of retainers. From the looks of the broken retainer and screw mount, someone’s already been inside this one. Now, set the seat upright and gently pull the seat cover and foam upward, exposing the aluminum seat structure that’s bolted to the track assembly.
The two front bolts (this is the passenger side) are easy; simply remove them. While we’re heard some seats have nuts here instead of bolts, ours had bolts. They screw directly into the brackets located on the front cross-shaft. Make a note of how the brackets are oriented so you’ll know how to reassemble them.
The rear two bolts are well back under the seat cover near the hinge. We pulled the foam and seat cover up enough to slip a hand underneath and put a socket onto the head of the bolt, then carefully slipped a 3/8-inch extension down through the hinge area of the seat cover until we could snap it into the socket and remove the bolt.
The body of the seat will now lay backward away from the seatback assembly, giving you access to the wiring and inflation components that need to be removed to finally free the seat from its bracket. This relay is held loosely in place on the wires supporting the seat foam and can be carefully lifted out of place without unplugging anything.
Disconnect the hoses that go from the inflator pump to the various bladders. We’ve already unplugged the light colored one in the lower left of the photo: the black one on the right remains in place. Release the latch and pull the plug directly downward off its long mounts.
This is the rear driver-side part of the assembly that lifts the seat. Notice the bracket to which the seat bolts, the cross-shaft that rotates the bracket up and down, and the flange into which the end of the cross-shaft is mounted. There’s a roll pin in the flange that retains the grooved end of the cross-shaft. Carefully drive it out, preferably with a roll pin punch that will keep from mushrooming the pin out and sticking it in its hole. We used one from gunsmithing supply house Brownell’s.
The flange is held on the seat track by a substantial rivet and the large T40 Torx bolt that holds the rear of the drive gear in place. Note this flange one isn’t broken yet, but it’s mostly a matter of time. If you haven’t already removed the drive gear as described above, do it now and replace the shims in the housing if needed. Grind the head off the rivet and drive it out with a punch. We suggest an air-powered hand grinder. You can do it with a Dremel, but we went through three abrasive wheels doing it.
The kit supplied by Corvette Central includes this stronger billet aluminum flange and a new roll pin, as well as the hardware to mount it to the seat track and four of the seat shims we covered earlier. Note that while the flanges are similar, there is a left and a right and you have to know which you need to order the correct kit. Grease the end of the cross-shaft prior to inserting it in the new flange, then drive in the roll pin in to lock the flange and cross-shaft together. We laid the flange on top of the head of a sledgehammer, using it as an ersatz anvil against which to hammer in the roll pin.
The new flange is mounted in place with this tower, bolt and washer. With the housing on the drive gear already inserted into the seat track and the drive gear partially in, set the tower over the drive gear as shown and slide the drive gear and tower into the track. Bolt the tower into place with the supplied screw through the hole once occupied by the rivet you ground out. Finish inserting the drive gear, but place the washer as shown between the drive gear mount bracket and the seat side of the track before inserting and tightening the T40 bolt that holds the bracket in place.
The new flange mounted in place. Reinstall the seat on the track, being careful to route all wiring and hoses the same way they were oriented before the seat came apart. You may find it’s easier to start the rear two bolts loosely by hand, then rotate the seat forward and tighten them once everything else is in place. Everything else is reinstalled in reverse order.
Photography by Jeremy D. Clough