Body Installation: C3 Corvette Restoration Guide (2023)

The rebuilding of your Corvette’s critical components has been a long process. After the body was repaired, painted, and sprayed with clear coat, the new paint was wet sanded and buffed with compound. The entire interior was cleaned and refitted with its new interior. Once the work was finished the completed body was stored in a safe, low-traffic area. You properly supported the body to avoid putting any unnecessary stress on it and cracking any of its fiberglass body panels. You left the completed and painted body on a dolly because that provides the most secure support.

This Tech Tip is From the Full Book “HOW TO RESTORE YOUR C3 CORVETTE: 1968-1982“. For a comprehensive guide on this entire subject you can visit this link:

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You are now ready to place the body onto the refurbished frame.

Power Brake Booster Installation

The power brake booster is mounted onto the firewall on Corvettes equipped with this option. Four nuts hold the booster in place and the master cylinder is attached to the front of the booster.

Master Cylinder Installation

Bench bleed the master cylinder before installing it to the firewall. First clamp the cylinder to a vise by using one of the two ears that are used to attach the unit to the firewall. Then remove the cover and fill it with clean brake fluid. Work the pushrod back and forth to force air from the outlets. Be careful not to damage the piston during this operation.

Remove all of the air before installing it into the car; using vacuum is the most effective way to do this. You can buy a master cylinder bleeder tool at your local auto parts store. With your tool in hand remove about 2 tablespoons of brake fluid from one of the discharge ports. Be sure to keep the reservoir full during this operation. When you are finished, seal off the ports with a cap or bolt to keep dirt out and fluid in during installation.

Mount the master cylinder onto the brake booster. If you do not have power brakes attach the master cylinder directly to the firewall.

The master cylinder is operated when the brake pedal is pushed. Force is transferred via a pushrod to the master cylinder piston, which moves forward. This force is applied to the primary piston spring, which moves a secondary piston forward at the same time. When these pistons move forward they cover the bypass holes and hydraulic pressure builds up actuating the pistons in the brake calipers. When the brakes are released the piston return springs force the fluid back through the brake lines into the master cylinder. At the end of the brake release excess brake fluid is returned to the reservoir through the bypass ports inside the master cylinder.

Steel lines connect the brass block to both sides of the master cylinder. A distribution block is not a proportioning valve; its function is to distribute the master cylinder fluid to all four wheels. It also measures line pressure difference under braking conditions to two separate braking systems. A warning light is connected to the block that illuminates a warning lamp on the dash if one of the braking systems fails.

Body and Frame Preparation

The frame has now been completely repaired and is free of damage and rust. The powdercoat finish will keep it this way for many miles. The suspension, brakes, and driveline components have all received attention and have been refurbished or replaced. All of the brake and fuel lines are new. With proper care, such as yearly flushing, they should provide excellent service. The gas tank and steering system have been installed, which completes the frame preparation process.

The frame is now ready for its Corvette body. This is where the industrial steel casters that were installed onto the dolly pay off. They rotate 360 degrees and make moving the body a breeze.

If you don’t have a lift, it is time to get some friends to help maneuver the body. One person at each corner of the car should have enough muscle power to lift the body and guide it into the correct position on the frame.

As I mentioned, both the coupe and convertible bodies are fitted with a steel frame called the birdcage. The fiberglass body panels are attached to this frame. The coupe is more rigid because a steel hoop is installed behind the passenger compartment that is secured to the windshield frame with a center steel support. This support is used to attach the twin roof panels.

Convertibles do not have this feature and great care must be taken when lifting these bodies. Having the doors installed on a convertible does provide some additional body support, but it’s best to take extra care.

At Van Steel the body was rolled into the lift area to begin the reassembly of the body to the frame. We used a four-point lift to complete this procedure. The four pads on the lift provide enough support to the birdcage to safely raise the body high enough to roll the frame under it.

It’s very important to position the lift pads on the very outside edges of the birdcage because there must be enough room for the frame rails to fit when the body is lowered onto the frame. Once the body is firmly resting on the lift pads, slowly lift it off its dolly. At this time, closely inspect the body to make sure it is sitting securely on the lift. If it is not secure, lower it back onto the dolly and reposition the lift pads until you are satisfied that it is secure.

After the dolly has been removed, roll the completed frame under the body. Double-check to make sure it is lined up correctly as you do not want to damage the newly painted fiberglass during the lowering procedure. Once the frame is in its correct position, place the body mount doughnuts into their correct location onto the frame.

Step-1: Move Body into Assembly Area

The steel casters that support the car are very maneuverable. It is always good to have friends on alert during your restoration process because you may need some help from time to time. Make sure the body is properly positioned and equally balanced on the dolly. Carefully and cautiously move the body across the shop floor on the dolly; everyone needs to work as a team. Be sure that the body does not slip off the dolly because you would not want to damage the body and crack the body work or the paint surface. Use extreme caution when using this method because of safety concerns.

Step-2: Locate Lift Arms

If using a lift, place the four lift arms onto the steel birdcage that surround the body. This birdcage is strong enough to support the body as long as the lift arms are placed correctly. It is important to lift the body evenly to eliminate any stress to the body panels during this procedure.

Step-3: Position Body Over Chassis

The bottom of the Corvette’s steel birdcage is under a lower panel that is usually covered with a trim piece or side pipes. This panel must be removed prior to lifting the body back onto the frame. Notice how close to the edge of the birdcage the lifting pads are placed. This was done to leave enough room to allow the body to be lowered onto the frame. If the pads are moved too far inward they hit the frame and have to be repositioned.

Step-4: Check Body Position

Make a final check to ensure that the body does not shift when it is lifted and to leave enough room to roll the frame under it. Once you are satisfied, roll the completed chassis into place beneath the body.

Body Installation

Confirm the body is securely sitting on the lift pads and then slowly raise the body high enough to clear the frame. Position the frame under the body and make sure all of the wires are out of the way. If a wire gets snagged, reassembly becomes more troublesome as you try to locate the broken connection. Make sure the body-mount doughnuts are still in the correct location. After this has been rechecked and everything is in order you can start lowering the body onto the frame.

Step-1: Identify Body Mounts

This diagram explains where each individual C3 body mount is fitted on all coupes. (Convertibles have an additional connection between mount No. 2 and No. 3 that is indicated by View A on the drawing.) Pay close attention to how the doughnuts and shims are located as each one is slightly different. The correct torque specifications are also indicated here. (Photo Courtesy Van Steel)

This 1973–1982 Van Steel bodymount kit includes all necessary partsand instructions to safely secure thebody to the frame. Van Steel alsooffers a 1968–1972 body mount kit.

Step-2: Connect Electrical Wires

It is very important to follow the GM body diagram when placing the mounts into their correctlocation on the frame. Some have their washers on the top while others do not. It all depends on the location. All of them must be installed onto the frame correctly prior to lowering the body. This body mount is fitted to the driver-side front bracket located under the front door. The attachment bolt is installed inside the body foot well where it is secured to the frame bracket after the body is lowered onto the frame. During the lowering process it is a good idea to routinely check to make sure that these doughnuts have not shifted. If they do, raise the body and reset the doughnuts. The left center body mount is identical to the one that is located in front of the door. If you have a convertible you need to install one additional doughnut on the frame. This one is located under the center of the door between mounts #2 and #3. Review Step No. 1 on page 161.

When the frame is in the correct location, lower the bodyslowly onto the frame. Only lift the body high enough toclear the highest obstacle on the frame to minimize therisk of the body falling off the lift pads.

As the body is being lowered onto the frame pay particular attention to the clearance in the engine compartment. The engine compartment on this generation Corvette is a very tight fit and any contact with an inner fender or firewall could cause extensive damage. Make sure no wires are hanging or have gotten caught on something that might rip or tear them from their mountings. We used a long-handle broom to snag the transmission shift cable that was laying underneath the car. We wanted to make sure it was on the driver’s side of the transmission as the body was lowered onto the frame. Failure to do this can crush or bend the cable so it is unusable. Do not be in a rush to complete this step. It is a good idea to lower the body a few inches and then stop to make sure the wiring and mechanical parts are clear.

Make room in the tight engine compartment by removing the air cleaner assembly. If you do, make sure the air intake on the carburetor is sealed so no stray part falls into it. This would be costly and time consuming to fix.

Connect the Steering

As the body is lowered onto the frame, pay particular attention to installing the steering column flexible coupling onto the steering gear. When the steering column reaches the steering gear, stop the drop while you line up each end of the steering column and the steering gear.

The shaft on the steering gear has a fl at flange on one side. It must be lined up to the flange inside the flexible coupling on the steering column. Work the two flanges back and forth until they are matched. Use a small hammer to gently tap the steering gear flange onto the steering gear shaft. When both units are coupled correctly tighten the bolts and resume lowering the body onto the frame.

Step-1: Align Steering Collar to Spline

Line up the steering column collar so it can be attached to the steering box spline. In addition position the brake lines to be installed onto the master cylinder.

It helps to have two people working on this task. One can turn the steering wheel while the other lines up the steering box with the steering column. These two parts need to be matched up as the body is being lowered onto the frame. The steering box spline has a fl at spot that helps it line up with the steering column collar.

Step-2: Seat Column on Spline

Once everything is lined up correctly, lightly tap on the steering column to seat it on the steering box spline. Make sure the fl at spot on the steering box spline is lined up correctly with the steering box collar before tightening the four bolts. These are 12-point 7/16-inch bolts that require the use of a 12-point socket to tighten them. Turn them until they stop. You want them tight, but be careful to not snap the heads off the bolts.

Install the Headlight Doors

Every C3 Corvette utilizes vacuum-operated headlight doors that retract into the nose when they are not in use. The engine provides pressure to the actuators. A manual override system is located underneath the steering column and the doors can be kept in the open position at the driver’s command. The vacuum system requires many lengthy rubber hoses to operate and a cracked or broken hose or connector can cause a vacuum leak in the engine.

Aftermarket Corvette suppliers, such as Lonestar Caliper Company, sell replacement headlight door parts.

Remove the Front Bumper Cover

If the bumper cover was installed onto your 1973–1982 car after it was painted to prevent it from wrinkling, remove it now. You need this extra working room to install the front bumper assembly that is hidden by this outside cover.

This step is not necessary for 1968–1972 Corvettes as they are equipped with a small bolt-on chrome bumper that can be installed easily.

Align Frame to Body

The frame and body have holes that are located near body mount #2 (see step 1 on page 161). To aid alignment place a rod through the hole in the lower door jamb and into the hole in the frame. This procedure keeps the body and frame in their correct front and rear locations. It also helps prevent any mechanical components from hitting various parts on the body as it is lowered onto the frame.

Once the body is on the frame measure the gap between the body and the frame. Both front and rear measurements should be the same on both sides of the car. You can shift the body by gently pushing on it until all of the measurements are the same.

Step-1: Lower Body onto Frame

Once the front bumper is removed, finish lowering the body onto the frame. Make sure that none of the rubber doughnuts have shifted out of place. If they have, slightly raise the body, readjust them, and lower the body back onto the frame.

Step-2: Align Body and Frame

Every frame has an alignment hole located behind mount #2 (see illustration on page 161). Its purpose is to line up the body, front to the back. (It also enables the fan and gas tank to align correctly during the body installation.) When these holes cleanly align, the body is properly aligned. Insert a socket extension into the hole to move the body forward and back or left and right depending on the adjustment required.

Measure the body/frame gap behind each wheel on both sides of the car. This helps verify that the body is square on the frame. The right and left sides should have the same measurements. They do not have to be precise but they should be very close.

Front Bumper Installation

As federal crash standards became progressively more stringent during the 1970s, Corvette engineers had to make the 5-mph crash bumper stronger. The 1973–1974 models are the lightest, while later models are stronger because they are fitted with more material.

The front bumper plays a vital role in securing the fiberglass nose to the frame. A metal support on the bumper is bolted to the nose on the underside of the body. This part of the front body is very heavy because it supports the weight of the headlights. The bumper brace helps to prevent cracks in the fiberglass. You might be tempted to omit this heavy metal part, but that is not recommended for street use as it does provide effective front-end protection in case of an accident.

Step-1: Assemble Crash Bumper

Corvettes built from 1973 to 1982 have some form of crash bumper attached to the front frame rails ahead of the engine and suspension. The bumper is concealed under a rubber cover. This 1980 Corvette uses a rubber egg crate material that serves as an energy absorption barrier in case of a sudden impact. It is attached to a steel frame with four bolts. Use a 5/8-inch socket to tighten and torque them to 60 ft-lbs. This unit bolts directly to the front of the frame to provide maximum strength. The center of the fiberglass nose is secured to the large black piece of metal in the center of the front bumper. Do not forget this bolt because the front overhang on these Corvettes is very long and breaks quickly if it is not attached to the bumper.

Step-2: Position FrontBumper

The bumper is an awkward component to install. It might be helpful to have a third person available to install the frame bolts while two people hold the bumper in place.

Step-3: Attach Front Bumper Brackets

Secure the bumper brackets to the frame with six bolts; use a 3/4-inch socket to attach them.

Here, two of the three 3/4-inch bolts and nuts per side are installed into the front frame rail. The missing third bolt will be inserted into the round black hole. Each one should be torqued to 75 ft-lbs.

One bolt attaches to the front bumper bracket from beneath the nose of the car. Be sure to include the rubber doughnut on top and a washer under the bolt. This bolt is very important to install because it prevents the nose from shifting or sagging. Use a 5/8-inch socket to secure to the body and torque it to 60 ft-lbs.

Secure the Body

When the body is resting on the frame and you have confirmed that the alignment is correct, insert the body bolts. (See step 1 on page 161 for the correct placements and torque specifications.) Before tightening them, it is a good idea to insert each one and turn it several times into the nut to make sure it lines up correctly. Once all bolts are started, tighten them beginning with No. 1 and moving toward the rear on each side of the car until they are all secured.

Fluid Level Check

You want to add the right fluid/ oils to the radiator, power steering, engine, brakes, automatic or manual transmission, differential, etc. Make sure these are all filled to factory specifications before you attempt to start your engine. This is also a good time to revisit your checklist to verify that all hose attachments and electrical fittings are connected correctly.

Brake Bleeding

The most common method to bleed your brakes is gravity (manual) bleeding. It is simple and effective but it requires two people.

The other method is pressure (or pedal) bleeding. This requires using diaphragm-type, mechanical pressure bleeding equipment that is usually found in repair shops.

All 1968–1982 Corvette are fitted with four-piston brake calipers that have bleeder valves on each side of the rear and one on the front caliper. Always be sure to use the correct brake fluid and never let the master cylinder run out of fluid or you will have to start the process all over again. When the system is finished bleeding, the pedal should be firm and not drop when you push it down.

Exhaust System Installation

All 1968–1974 Corvettes came from the factory with true dual exhausts. Each side of the engine had its own dedicated exhaust system that feeds into two large mufflers underneath the bumpers. Only 1969 Corvettes were available with the optional factory side-mounted exhaust system (N14) that exited under each door. Each of these pipes had a built-in muffler to help reduce the exhaust noise. You will know if sidepipes are installed on any other year except a 1969; they are not factory original. However, these pipes are very popular with C3 owners and a lot of cars have them installed. If the noise doesn’t bother you and your car is not being judged at an NCRS meet, enjoy them!

Corvettes built from 1975 to 1982 have two pipes that feed into one catalytic converter under the passenger compartment and then split back into two pipes that lead to the mufflers. These cars are equipped with an air pump that feeds air into the converter to help emissions. If you live in a state with emissions inspections, this system is necessary to pass the annual test.

Vacuum Line Connections

It is very important to carefully inspect every vacuum line that exits the engine. These lines should be soft and flexible when squeezed. If they are hard and brittle, they are old and prone to fail, so you need to replace them.

The basic system is fairly simple to troubleshoot. It uses vacuum from the engine to open and close the headlight doors. If your car is a 1968 to 1972 this system also operates the hideaway windshield wiper door.

Both doors actually have two subsystems: control and operating. After your car is reassembled and these systems do not work, troubleshoot each one separately. The control system opens and closes the headlight and windshield wiper door. The wiper door system (which was eliminated starting in 1973) contains the wiper door safety switch that is between the override and the wiper actuator relay. This relay prevents the door from closing until the wiper blades are in their parked position.

Wiper Doors

The wiper door system is very similar to headlight door operation. The main difference is that the headlight door system has two actuator relays and actuators compared to one for the wiper door. The other difference is that the headlight system does not need a safety switch to protect another system in case of failure.

Operation of the wiper system begins at the vacuum source, which is located on the intake manifold. The line goes through a filter and a check valve, then out of the lower fitting on the valve to the windshield wiper switch that is in the off position. When the wiper door is opened, vacuum is not allowed to reach the wiper actuator relay valve without vacuum present. A spring in the actuator valve pushes a diaphragm to open the wiper door. In effect all it is doing is routing the vacuum from the intake manifold to the actuators (vacuum motors) to open and close the doors.

If you have a vacuum leak that does not allow you to open your headlights or operate the wiper door your engine is probably running rough. You will have to find the leak and repair it.

Headlights

This system consists of vacuum hoses, vacuum hose filter, one-way check valve, headlight switch, manual override switch under the steering wheel, vacuum accumulator (storage tank), relays, and two actuators (vacuum motors). You need a vacuum gauge to troubleshoot the system.

Disconnect the headlight/wiper door vacuum line where it connects to the intake manifold with the engine running. Connect a vacuum gauge directly to the manifold outlet. The engine should produce 18 to 20 inches of mercury according to the gauge. If you discover a 2- to 3-inch drop anywhere in the system, you have a leaking hose. If your car has a high-performance cam with excessive valve overlap, your vacuum reading is much lower; as a result the headlights slowly open if they are working correctly.

If your lights or wiper door is not opening, isolate the system to find the leak. If you have both wiper and headlight systems unhook the wiper door circuit and plug it with a golf tee or something similar. If it is too hard to reach, lower the panel under your steering column and plug the wiper override hose by disconnecting it from the switch.

Be sure to check the amount of vacuum coming into and out of this switch before proceeding. Make sure there is only one path back to the source of the vacuum (intake manifold) when testing an individual line.

If a reading is within 2 to 3 inches, that particular vacuum line is fine. If there is a significant drop, troubleshoot that line to find the leak. If all the vacuum lines are close to specifications and the doors are staying open, it indicates that a diaphragm has a hole in it and is leaking.

The actuators have a springloaded diaphragm inside and operate with vacuum. If the actuator is not getting vacuum, that relay stays in the up position at all times. A C3 Corvette with one light up and the other one down has a leaking diaphragm.

Reservoir and Actuators

The reservoir is easy to test. Remove both of the lines that go to the actuators. Plug one of the outlets where you just removed the lines and put your vacuum gauge on the other side and check the reading. If it is below the normal operational range, the reservoir is leaking.

On all 1973–1979 Corvettes the vacuum reservoir is in the round cross member underneath the headlights. This cross member has three fittings: one on the driver’s side and two in the center to provide vacuum to the headlight relays.

If the reservoir is within specification, check the two headlight actuators. Test them the same way you checked the rest of the system until the part that failed is located.

Air Conditioning System

If your car is equipped with air conditioning and no seals were broken during disassembly, return the compressor to its bracket on the engine. Take the system to a shop that specializes in air-conditioning services and repairs if you are not familiar with it.

Most of the parts are available from Corvette aftermarket supply houses. Many auto parts stores stock rebuilt compressors at a reduced price. You can even buy duplicate factory stickers to paste onto rebuilt compressors.

C3 Corvettes were produced with two types of air conditioning systems. The original A6 compressor was an axial-flow unit that used R-12 freon for refrigerant. R-12 was banned due to environmental concerns and was replaced with R-134 refrigerant.

Later C3 Corvettes began using a rotary A/C compressor that was lighter and more efficient but still used R-12 as refrigerant. If the system was left intact when the car was dismantled, it can be quickly reinstalled onto the engine.

However, if the system was removed and has been open to the atmosphere for an extended time, a number of parts must be replaced before it is recharged. Some of these parts include the drier/accumulator, expansion valve, condenser, and maybe even the compressor. Older C3 Corvette A/C systems must be converted to use the new R-134 refrigerant.

Odds and Ends

Now it is time to connect the battery and turn on the electrical system. It is a good idea to test anything that is powered by electricity by turning it on. This includes dash lights, interior lights, headlights, taillights, and radio. You need to make sure your tunes work.

Look closely at all hoses to make sure they are tight and all fluids are filled to factory specifications. Leave the hood off until you have run the engine for a while so you can check for leaks or loose connections.

Add some gasoline and turn the engine over a few times to make sure no gas is leaking anywhere.

The only remaining items to be installed are the rear bumper, hood, and the trim rings on the wheels.

T-Top Adjustments

C3 Corvette coupes were fitted with two removable T-tops. They were designed to be stored behind the seats or on an optional luggage rack. From 1968 to 1977 only fiberglass roof panels were available. In 1978 new laminated glass roof panels were introduced (option code CC1) and became a popular addition.

The 1968–1977 T-tops had dual pull-down latches to hold them in place. One latch was located at the front of the top and one was at the rear. Two pins were inserted into the T-bar and the outside latches secured the tops to the birdcage. In 1978 the rear latch was eliminated and replaced with a movable pin that was part of the standard anti theft alarm system.

The roof panel gap (down the center of the T-bar) should be no more than 1/2 inch wide. The tops should sit 1/16 to 1/8 inch from the roof behind the seats. Loosen the retaining bolts and move both tops until you get the correct measurements. Tighten the attaching points with the roof in place.

The glass roofs are designed to sit 1/8 inch higher than the rear roof. They should not be adjusted lower than this as they might break from stress.

Use an 8 x 10-inch sheet of paper to determine if your tops are fitting snugly onto their gaskets. Put the paper on the gasket and install the roof. If the paper slides out easily from between the two, the top needs adjustment. Repeat this process until the paper cannot easily be pulled out.

Road Test

Art Dorsett’s completed 1980 Corvette was given a 20-minute road test to check its brakes and fluid levels, and to verify that the transmission shifts correctly. The engine temperatures and oil pressure were all normal. This car passed the road test successfully and it was sent to the alignment shop to receive a fourwheel alignment.

Final Cleaning

You are joining a unique club as a Corvette owner. The majority of owners take pride in how their car looks, and it is not unusual to see them cleaning their cars on a Saturday afternoon. Detailing your Corvette can be a very complex task, starting with deciding which products to use. There are a large number of brands being sold over the counter, and each one claims that it is the best on the market. The final decision on the best one to pick rests on you. Talk to your friends and other Corvette owners to get their opinion on the best products. Today simple waxes have expanded to glazes, cleaners, polishes, sealers, etc.

Written by Walt Thurn and Posted with Permission of CarTechBooks