Tech Tips: C3 Chevrolet Corvette

Meet the Expert:

R.J. Schmieder
Automotive Sourcing Manager
Eckler Family of Automotive Groups
5200 S. Washington Ave.
Titusville, FL 32780


GM added vacuum-actuated pop-up headlights to the Corvette in 1968 and they continued all the way through to 1982. Owners of these cars have had issues with slow-opening or falling headlights. 

As the Corvette ages, the headlights develop problems because the rubber deteriorates. Usually, the hose will crack around the attachment points on the headlight actuators, valves, tank or at the engine. Each connection needs to be checked and, if cracked, a small portion of the hose can be trimmed and then reattached to create a leak-free connection. 

The other area to address is at the headlight valves. These valves have a sponge-type material that allows air in. Over time they get filled with dirt, which restricts airflow and makes them slow to open. Address these areas and your headlights should function like new.

Tachometers on 1968-’74 Corvettes are cable-driven from the distributor. Just like a speedometer cable, the ends will wear and cause the tach needle to bounce or give an unsteady reading. Replacing the inner cable or just the complete cable and casing (Eckler’s Corvette part No. A3501) will resolve this problem. 

If your tach isn’t working at all, the problem most likely lies in the tachometer gears inside the distributor. Remove the small bronze coupler on the side of the distributor, then inspect both the small gear in the coupler as well as the distributor main shaft. If the small gear shows signs of wear, it’s likely the distributor main shaft will, too. 

To fix this, remove the distributor from the engine. Then replace the main shaft (part No. A2428 or 51154), small gear (part No. 25160) and coupler (part No. 27280). There is a small plastic button (part No. A2763) inside the distributor that will also need replacing. Do the job once, but do it right. 

Sagging outside-door-handle covers can be replaced, but this involves removing the inner door panel, removing all the rods and then unbolting the handle from inside. There is a much simpler way to solve this problem: Just purchase one of the handle springs (part No. A4302 or 55979). These great little inventions will put the handle cover in its proper place and look like new without all the work.

These springs are simply placed into the handle from the outside and cover the original spring. Once pushed inside the handle, the spring releases and pushes the cover up to its original position. They’re stainless steel, so they will last for many years.

C3 Corvettes are known for cooling issues. Replacing the radiator alone may not solve your problem. Inspect your fan shroud, fan blade and fan clutch. All these items can cause problems. Inspect for a good seal between the radiator and its support, and between the radiator and the fan shroud. Check that the fan clutch works properly, and make certain the radiator is clean inside the vanes. 

Many times all these items are okay, but the C3 Corvette changes the way you need to think about cooling. Air doesn’t enter from the front of the car, it enters from underneath. All cooling air is picked up off the road, pushed up into the front of the radiator and then through it. The one item everyone forgets is the spoiler (part No. A2983, A2993 or 40032). This was not put there for looks: It works. 

If no spoiler is installed, the air will pass under the car and never go through the radiator. It is a must to have either the original spoiler or even an aftermarket spoiler in place to keep things cool. 

Hood alignment issues are simple to fix. First, purchase several rubber hood alignment bumpers (part No. A2069, 41505 or 37720). Then adjust your hood to bring the highest portion of the hood level with the fender. This will cause the lower section to be lower still. 

Place some masking tape on the fender and across to the hood at each low spot so you know where to position these bumpers. Open the hood and measure the thickness of the hood edge. Place the hood alignment bumper inside the tray edge at the tape mark. Using the measurement of the hood thickness, measure down from the fender top edge and mark the inner surface.  

The hood alignment bumper will need to be trimmed to match the distance from the mark to the tray. Once it’s trimmed, place the hood bumper in position, lower the hood to touch and let it sit in the sun. Fiberglass flexes as it warms up, so the hood will slowly drop at the rear until it is in perfect alignment with the fenders. Do this for both sides and your hood will fit properly.

Meet the Expert:

Matt Gessler
Marketing Manager
Corvette Central
13550 Three Oaks Road Sawyer, MI 49125


Front and rear wheel bearings should have minimal play without adding drag to the wheel assembly. GM suggests .001 to .005 inch of movement. Do not preload the bearings: Tighten them while spinning the wheel until there is slight (12 lb.-ft.) pressure on the spindle nut. If the cotter pin hole is not aligned, move it to the loose side to install. Check adjustment play by moving the wheel a few times.

The rear wheel bearings should be held so that there’s close to .001 inch of play. These bearings are not adjustable except during servicing. Shims set end-play and require specific tools to service. If there is excessive play, expect to disassemble and replace the rear wheel bearings. While doing this, have the trailing arm bushings checked for deterioration.

For the best possible ride and handling on a C3, replace the rear leaf spring (composed of steel leaves) with a fiberglass mono-leaf spring. Using one will allow you to keep tire pressures at the recommended levels without the associated harsh ride.

Positive caster loads the spindle, making the wheels want to naturally position themselves straight ahead. This stance makes for excellent high-speed handling, but you should expect increased steering load as more positive caster is adjusted into the suspension. That’s one of the reasons the C3 Corvette has less positive caster than the C4-C6 Corvettes. The original equipment control arms will not allow more than 3.75 degrees of positive caster.

1968-’82 Corvette Performance Alignment Specifications:

Caster: positive 3.25 degrees (plus or minus 0.25). There should be no more than a 0.5-degree variation from side to side. To offset for crowned roads, set the left caster to positive 2.75 degrees and the right to positive 3.25 degrees. Some C3 Corvettes will allow positive 3.25 degrees while others may allow another 0.25 degree. The idea is to maximize positive caster. This change will require more effort during turning but allow the steering wheel to return to center more quickly.

Camber: negative 0.5 to negative 0.75 degrees front and rear. Track-only cars: negative 1.25 degrees front and rear.

Toe: positive 0.25-inch total for
both wheels.

Factory Settings

Caster: positive 2.25 degrees (plus or minus 0.25 degree). Decrease left side caster 0.5 degree for crowned roads.

Camber: 0 to positive 1.5 degrees

Toe: positive 0.125 to positive 0.25 inch.

The Corvette’s fuel tank is slightly higher than the carburetor to allow gravity-powered fuel feeding. It’s important to frequently check the condition of the hose at the fuel pump and tank. A leaking hose can empty an entire fuel tank overnight. Check the engine oil for fuel contamination if the fuel pump fails. Cars from 1968 to ’74 have fuel sending units at the bottom of the tank. These are more accessible, but they will not stop flowing fuel until the tank is empty.

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