As discussed in Chapter 1, the C3 Frame design was carried over from the 1963–1967 C2 Corvettes. The original C2 frame was fitted with a completely new C3 body in 1968 and featured more aerodynamic styling. The knife-blade upper front end that housed the headlights in the C2 was replaced with a lower and smoother nose on the C3. This greatly reduced the car’s tendency to lift at high speeds and it became a much more stable sports car. At the rear a small spoiler helps to keep the rear planted to the pavement.
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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This new Shark design proved to be very popular with Corvette owners, and that popularity helped to keep this car in production in various forms for 14 years. The body changes were subtle during its entire production run. Minor styling changes were made to the 1968–1972 models, including door handles, side vents, and exhaust tips. In 1973 an injection-molded urethane bumper cover, new hood, and front fender vents were installed on the Corvette. In 1974, a rear crash bumper was introduced. A large rear window was added in 1978 and new front and rear bumper covers were added in 1980; these remained to the end of production in 1982.
The original C2 frame design was very robust yet inexpensive to produce, and many C2 parts interchanged with the C3. The frame is a boxed-steel design and almost identical from 1968 to 1979. The 1980–1982 Corvettes were fitted with different rear frame rails to accommodate the new aluminum rear axle housing, but the rest of the frame is similar.
To control costs Corvette engineers used many existing front suspension components from the standard GM passenger car line. Up front, stamped-steel upper and lower control arms, supported by coil springs, were installed. Rubber bushings reduced noise and vibration. A transverse leaf spring rear suspension that uses stamped-steel trailing arms is unique to Corvette. While this front and rear design is much heavier than on newer Corvettes, it has proven to be trouble free.
When restoring a Corvette body and frame, pull the engine and transmission because it opens up a lot of working space and allows you to easily disassemble and inspect the rest of the frame’s components.
Carefully remove all of the components from the frame and make a parts list. Each removed part be cleaned and inspected to determine if it is reusable. If it is not, a replacement part should be added to your purchase list. If the old part is reusable it should be bagged, tagged, and stored.
The downside of the boxed design is that it tends to collect water and salt in the inside of the box in critical strength areas. If this is not managed correctly the frame becomes heavily corroded and rusts.
You should closely inspect the frame rails in front of the back wheels because this area typically experiences heavy corrosion. Another spot to carefully inspect is behind the front wheels. This area accumulates a large amount of road moisture and is slow to dry out.
However, some frame corrosion is not catastrophic. If you locate some trouble spots that were not visible during your inspection they can be repaired. This is because almost any part of the C3 frame is available from aftermarket suppliers. It is worthwhile for aftermarket suppliers to keep producing these parts because of the cars’ popularity. Suppliers such as Van Steel are equipped with a frame jig that allows them to check the frame’s measurements against factory specifications. Rusted parts can be removed and new replacement sections can be welded back in with no loss of strength.
The C3 frame holds all of the working parts that give the C3 strength and performance. Careful inspection and disassembly of each part helps determine what to replace, refurbish, or reuse. Remember that suspension, steering, and brake assemblies are put under tremendous stress during spirited driving. It’s vital for your safety that you replace any worn or damaged parts with new or refurbished parts. It is money well spent and will provide many miles of enjoyable and safe driving.
Engine and Transmission Removal
After all of the fuel lines and electrical connections have been removed start removing the engine, transmission, and driveshaft from the frame. They are connected with two forward motor mounts and the two bolts below the rear of the transmission. The driveshaft is connected with bolts at the differential and a yoke at the front of the driveshaft. Connect a hoist onto the engine prior to unbolting any of these components to prevent damage.
After the engine and transmission have been removed, use a four point lift or a floor jack to lift the frame and place it on safety stands. This allows access to the parts on the top and bottom of the frame that need to be removed. Once the frame has been securely lifted off the garage floor, remove the wheels. Inspect the suspension for damaged, bent, or broken components prior to removal. This is a good time to take photographs and make notes on what you discover.
Front Suspension Removal
The C3 front suspension design is very similar to that of other passenger cars of that era. The upper and lower control arms are stamped steel and are secured to the frame with bolts, brackets, and bushings. A coil spring is located between the upper and lower control arms. A cast-steel steering knuckle is secured to the control arms with ball joints. The knuckle holds the wheel spindle, wheel bearings, brakes, steering, and anti-roll bar fittings.
When disassembling the suspension take great care as the coil spring is compressed and under pressure. You cannot allow the compressed spring to slip because it could cause serious injury.
The front shocks are located inside the upper and lower control arms in the front suspension. The are secured with three bolts and because of the way the suspension is designed, the opening in the lower control arm limits the size of a replacement shock. Pay particular of the shocks during the removal process. Make sure any replacements that you are considering fit into this opening before ordering new ones.
Anti-roll bars help prevent the Corvette from leaning too severely during hard corning. Large bars on the front and rear reduce this tendency, but can produce a harsher ride if they are too stiff. Spring rate and shock absorber damping also determine your car’s ride quality. Think carefully about how you will be using your Corvette. For example, will you use it as a daily driver, weekend cruiser, autocrosser, or a road racer at your local racetrack? Your decision impacts how stiff or soft you want your suspension to ride. The base suspension from the factory is the softest; the F41 or FE7 optional suspensions are the firmest.
Small-block Corvettes were equipped with front anti-roll bars if they were not ordered with the optional F41 or FE7 sport suspension packages. Big-block cars featured a rear anti-roll bar. The rear bar improves handling in tight turns and is usually a worthy addition if your car is not equipped with one. Many aftermarket performance companies offer a wide variety of replacement anti-roll bars. A good size to start with for a C3 is a 1-1/8- inch bar in the front and a 3/4-inch bar in the rear. This size is a good compromise between a reasonably compliant ride and precise cornering capabilities.
Smaller front bars increase body roll but produce a smoother ride. However, if you are happy with the way your car handles and it is not equipped with a rear anti-roll bar stick with this setup, but install new rubber bushings.
Corvettes built between 1968 and 1975 were equipped with manual or power-assisted steering (N41). Starting in 1976, the base price was increased to include this option as standard equipment. However, 173 Corvettes delivered in 1976 did not have power steering. All 1978–1982 Corvettes were equipped with N41 as part of their standard equipment.
The manual steering system is connected on each front suspension knuckle with a tie rod end. A series of rods are connected and one rod is connected to the steering box swing arm. It is secured with a 3/4-inch nut and held in place with a cotter key. Cars equipped with power steering have an additional hydraulic ram that is connected to the frame for support and needs to be removed from the frame during disassembly. A power valve is connected to the steering swing arm and is also secured with a 3/4-inch nut.
The steering box is located on the left side of the frame rail right behind the upper control arm. This heavy unit is attached to the frame with three bolts. Most of these boxes usually need an overhaul to eliminate play in the steering caused by high mileage or spirited driving.
This is a perfect time to look into buying a refurbished unit. Many specialty shops can rebuild your old unit or exchange it for one that has been refurbished.
All C3 Corvettes are equipped with four-piston disc brake calipers in the front and rear. A 1/4-inch hose feeds fluid to the calipers, which are held in place with two bolts at each wheel. These calipers left the factory without stainless-steel inserts and were prone to rusting and leaking early in their life. In 1965 an aftermarket vendor developed a process to insert stainless-steel sleeves into each piston cylinder, which pretty much solved this leaking problem. If the brakes are not leaking, they probably have these inserts. Refurbished calipers feature stainlesssteel inserts along with new pistons, seals, and gaskets.
Front Steering Knuckles
Each front suspension upper and lower control arm is connected to a steering knuckle at the top and bottom. This knuckle serves several purposes: braking, steering, and connecting the suspension. These sturdy units rarely need replacing unless they are bent or the spindle is rusted or damaged.
After the knuckles have been removed, carefully inspect them for any fl aws. Replacement units are available. Be sure to save all of the bolts and mark them accordingly.
Front Suspension Spring Removal
Step-1: Position Frame and Floor Jack
Place a floor jack under the lower control arm. Raise the floor jack. This prevents the coil spring from coming loose during suspension disassembly. Leave about 1 inch of clearance between the jack and the lower control arm. This allows room for the suspension to clear the upper ball joint when the bolt is loosened. Leave the upper ball joint nut on the stud to prevent the spring from exiting its spring cradle. Double-check to make sure the frame is properly secured. The next steps are easier if the engine is installed or several helpers are sitting on the frame to add weight.
Step-2: Remove Ball Joint
After removing the cotter pin from the upper ball joint nut, use a 3/4-inch wrench to loosen but not remove the nut from the ball join Strike the front suspension steering knuckle with a mallet until it drops onto the 3/4-inch ball joint nut. Continue to keep the floor jack firmly up against the lower control arm after the knuckle drops down onto the bolt. This prevents the spring from breaking free of the upper ball joint. Keep the spring in its mounted position until it’s time to remove it. A spring that slips during this process can cause serious injury, so exercise the utmost caution. Don’t take chances with your safety.
Use a 7/8-inch wrench to remove the lower control arm ball joint nut. Again do not forget to extract the cotter key prior to taking the nut off.
Raise the jack high enough to allow removal of the 3/4-inch ball joint nut. Once the nut has been removed, slowly lower the jack until the steering knuckle is free from the ball joint. Lower the knuckle (shown). Now lower the jack to the fully down position, but do not remove it.
Step-3: Remove Spring
Carefully grab the spring to determine if it is loose in the upper and lower control arm housing. If it is loose enough, remove it (shown). Do not force it if it is not loose. The bottom control arm needs to be lowered. If the control arm is difficult to lower, loosen the two 5/8-inch bolts on the front and rear of the control arm bushings. You do not want this spring under any tension. If it is free remove it from the control arms. Once the spring is free, use the jack to raise the suspension knuckle back to the top ball joint stud and reattach the 3/4-inch nut, turning it about four turns. Lower the jack. Strike the lower ball joint with a mallet until the upright is free from the lower control arm. Now the top nut can be removed along with the upright. Again, be careful when removing this part as it is a heavy unit.
Control Arm Removal
Upper Control Arm
A floating arm is attached to the upper steel stamped control arm, which uses rubber (factory) or poly (aftermarket) bushings. Two bolts secure the shaft in place. The shaft has two holes so two bolts can be put through them to attach the arm to the frame. Nuts secure the arm to the frame. Place shims between each shaft and frame to align the front suspension. Straight frames usually have one or two shims at each bolt. If you find an excessive number of shims, the frame may be damaged. If you notice a lot of shims on one side of the car, the frame’s condition can be verified when it is completely disassembled and put on a frame alignment rack. The correct measurements can be provided by Van Steel or your local body shop.
Repeat this process on the other side of the front suspension. The top of the coil spring is held in place with this unit.
Lower Control Arm
The lower control arm is also made of stamped steel and features a steel shaft supported by rubber or poly bushings. The bushings are screwed into the shaft at each end with bolts holding it together. This arm serves as the resting place for the bottom of the coil spring. It is also used to attach the bottom of the shock absorber.
The anti-roll bar also attaches to the lower control arm. The arm fits into two metal channels under the frame below the engine. A small metal plate sits on top of the lower frame at the front flange. The front two bolts on the control arm shaft are bolted to this plate.
Rear Suspension Removal
In 1963, General Motors introduced the first independent rear suspension system on the Corvette, and the design was carried over and fitted to all C3 models. It features two stamped-steel trailing arms that are held in place with a single bolt at the front of the wheel well. The trailing arms house the parking brake, brake rotor, shock absorber mount, and rear spring attachment points. A transverse multileaf steel spring is bolted to the differential and connected to each trailing arm with a link. In 1981 automatic Corvettes with standard suspension were equipped with the new fiberglass-reinforced transverse rear spring; it became a standard spring material for the front and rear of all 1984 and later Corvettes.
Rear Leaf Spring
All C3 Corvettes left the factory with three types of rear springs.Two were metal and were offered in nine leaves for standard suspension cars and seven leaves for heavy-duty applications. The third type was a fiberglass-reinforced rear spring that became available in 1981 for cars with automatic transmissions and standard suspensions. The metal springs were bundled together in the middle and bolted to the rear differential with four bolts. These springs are very heavy and can cause serious injury if not handled correctly.
Before removing a spring, check to see if the rear of the car is sagging on one side or the other. This could indicate bad adjustment on the end links, spring weakness, or metal failure. These springs are very strong and rarely fail, but failure is possible so it’s best to check them now. Look for cracking in the spring surface, bent leaves, or severe rust that has worked its way through the metal.
The rear shocks perform an important function in the operation of the rear suspension. The lower shock mounting is attached at the rear of the trailing arm and the top is bolted to the frame. Both attachment points help control the movement of the rear spring and trailing arm travel.
Tire technology has made giant leaps forward since these cars left the factory. A good set of shocks can help your C3 handle the improved traction capabilities of new tire technology.
Strut Rod Removal
Step-1: Remove Lower Shock Cotter Pin
Use a pliers to flatten and remove the cotter pin from the lower rear shock mount bolt. Use a 15/16-inch socket to remove the nut.
Step-2: Remove Lower Shock Nut
Use a 3/4-inch wrench to remove the nut from the mount. The lower part of the rear shock can be removed from the shock mount.
Step-3: Pry Shock Mount from Trailing Arm
Place a large pry bar between the shock and the strut rod to begin removing the shock mount from the trailing arm assembly. This shock mount needs to be completely removed before the trailing arm can be released.
Step-4: Drive Shock Mount from Trailing Arm
Attach a special nut (available at most Corvette supply stores) to the shock mount stud to prevent damaging the threads on the mount. Once the nut is installed, use a mallet to strike the nut until it is flush with the rear suspension upright.
Once the nut is flush, remove it and place a large center punch onto the middle of the bolt. Strike the bolt with a mallet until the shock mount is completely free from the suspension upright.
Step-5: Pull Trailing Arm from Suspension
Apply upward pressure on the trailing arm to release the strut rod from the suspension. Pull the strut rods straight down to the vertical position to prepare for the next step.
Step-6: Mark Strut Rod Washers and Nuts
Before removing the strut rods apply a dab of paint to the bracket and the strut rod washers, so the washers and nuts can be returned to the same side during reassembly. The washers adjust the rear suspension camber settings. Marking them with paint saves the previous settings (if they were correct). Use two 3/4-inch wrenches to remove the strut rod bolts from the bracket.
The independent rear suspension on C3 Corvettes is far different than a solid axle rear suspension in a muscle car. The Corvette trailing arms are connected to the rear differential with two axles called halfshafts. A U-joint is attached to each end of the half-shaft. This allows the shaft to move up and down with the suspension movement. (Big-block cars use larger bolts to compensate for the extra torque of those engines. However, the design philosophy is identical.) When removing these units, carefully inspect the universal joints for signs of rust and grinding as you rotate them. They should be completely free of noise and rust. If they have any of these indications replace them.
Brake Calipers and Rotors
Two large bolts hold each brake caliper in place. Each caliper is purpose built for the wheel it is attached to, and you should always inspect each one for leaks before removal. You need to completely remove the calipers from the car.
With the caliper still attached, place the end of the brake hose into a plastic bottle. Push each caliper piston flush with the bore to evacuate the old fluid from the caliper. After all of the fluid is removed, seal the plastic container and dispose of it at a recycling center. Brake fluid is caustic so be very careful not to spill any during this process. If you spill it on a painted surface, it may remove the paint.
Most rotors can be removed easily unless they have been riveted. If they are riveted, drill the rivets out prior to attempting to remove them. Remember, the parking brake assembly is located beneath the rear rotor.
The differential is one of the bulkiest components to remove. Made of heavy cast metal, it is built to withstand all of the abuse and power sent to the rear wheels. It is easiest to remove while it is still attached to part of the frame, but out of the car.
Differential and Driveshaft Removal
Step-1: Remove Nuts
Remove the nuts that secure the half-shafts to the differential. Two attachment methods are used to secure the shaft to the differential. One is a heavy-duty cap on high-horsepower cars. The other uses a U-bolt (shown) on low-horsepower cars. Use a 9/16-inch socket or wrench to remove them.
Step-2: Remove Pinion Mounting Bolt
Use a 5/8-inch wrench on the top and an 11/16- inch socket on the bottom of the front pinion-mounting bolt to remove the bolt. The differential is resting on the frame and once the nut is removed the bolt should be easy to remove.
Step-3: Remove Differential
Place a floor jack under the center of the differential and firmly support it because you don’t want it to hit the garage floor and sustain damage. Loosen but do not remove the two 5/8-inch bolts that are under the transverse frame. These two bolts hold the differential in place. Use a long pry bar to work the frame loose from the side rails. Once it is loose, make sure the jack is supporting the frame. Now remove the two 5/8-inch bolts. At this stage, the floor jack is supporting the differential, so be careful.
Slowly lower the jack to release the differential from the frame. Once it has cleared the frame, roll the unit out and store it in a safe location for further disassembly. Keep in mind that the Corvette differential weighs 105 pounds, so it takes some muscle to lift it off the jack.
Rear Trailing Arms
One large bolt holds each of the two rear trailing arms in place. Located in front of the wheel well, this bolt serves as a pivot point for suspension movement and alignment settings. Steel shims are used to adjust the rear toe on the trailing arms, so you should pay particular attention when removing these arms from the frame. Make a note of the amount and thickness of these shims when they are removed.
Trailing Arm Removal
Step-1: Remove Trailing Arm Fasteners
A 5/8-inch bolt holds each rear trailing arm in place. This bolt runs from the inside to the outside of the rear frame in front of the rear wheels. An 11/16- inch nut holds the bolt in place and it is located on the outside of the frame; it’s held in place with a cotter pin. Use a pliers and hammer to drive out the cotterpin from the nut before removing the trailing arm bolt. Use a 5/8-inch wrench on the inside and an 11/16-inch wrench on the outside to remove the nut.
Step-2: Remove Trailing Arm Bolt
Once the nut has been removed, strike the bolt with a mallet to drive the bolt through the frame. This exposes the head of the bolt to allow enough room to wedge it out of the frame on the inside. This bolt needs to be completely free of the frame before you can remove the trailing arm.
Step-3: Pry Out Trailing Arm Bolt
Place a notched pry bar on the exposed trailing arm bolt. Rock the pry bar back and forth to work the bolt out of the frame. You may have to place a wrench between the frame and the pry bar to get more leverage to get the bolt completely out of the frame.
Step-4: Separate Trailing Arm from Frame
Once the bolt has been freed, remove the trailing arm from the frame. If the trailing arms are not bent or damaged, suspension companies can restore them. They can repair, sandblast, powdercoat, and install new bearings for minimal cost.
Remaining Frame Parts Removal
The fuel and brake lines need to be completely removed along with the parking brake cable and pulleys. Make sure all bolts have been removed before continuing.
Most Corvette specialty shops price their frame repairs based on how many original parts can be refurbished and the condition of the frame. If the suspension components are in good condition, they can be reconditioned and reused. Parts that cannot be reconditioned must be replaced with new parts. This includes bearings, fuel/brake lines, and rubber bushings.
A shop can usually remove the suspension, sandblast/powdercoat the frame, refurbish parts, and reinstall the refurbished parts in about three weeks. If you do the work yourself, your frame can be repaired, sand/ bead blasted and powder coated in a much shorter time at a greatly reduced cost.
Common problem areas on C3 frames include the underside of the front cross member. Damage occurs in this area when contact is made with a curb or a manhole cover. Rust often develops after it is damaged.
Rust is also a problem on frames that come from colder areas with salt-laden roads. It is often found where the main frame connects to the rails that support the rear suspension. Rust around the body bolt mounts is common, particularly on those located under the windshield post. Also carefully check the two rear mounts behind the rear wheels as they receive a lot of moisture. Almost any damaged frame can be repaired thanks to the large availability of new old stock (NOS) frame parts.
Straighten Damaged Frame Sections
Once the frame has been disassembled, inspect for damage and trueness. A steel brush is used locate and clean off the serial number. This is a good way to find out if the serial number or VIN matches the VIN plate on the body. If it doesn’t match, the frame is not original. This means it is not a numbers matching car and cannot be resold as one.
Closely inspect the lower control arm mounts that are welded to the rear of the front cross member under the engine. These are prone to breaking welds and must be repaired. A straight, aluminum, boxed bar cut t 26-3/8 inches is used to determine if the front frame cradle is bent. Again this is a common problem and can be corrected on a frame alignment rack.
As I mentioned earlier, the front sub frame on a C3 Corvette can bottom out on curbs, manhole covers, and other road anomalies and incur damage. The damaged sub frame section can be removed and the surrounding metal repaired. A new replacement section can be installed once the old part is removed and the surrounding area is ground smooth. After a new section is installed and the weld marks are ground down, the repair becomes invisible.
All frames are placed on a frame alignment rack before they are powder coated. The correct measurements can be found at your local body shop or by calling Van Steel to determine if the frame meets factory specifications.
Rust is the common enemy of steel parts on C3 Corvette frames. Water usually collects near the wheels and over time the frame rusts. Each rusted section can be replaced by welding a new NOS section into place. All welding should be done on the frame alignment rack to verify the frame alignment is correct. New sections are reinforced with smaller steel box inserts, tack welded together into place, and then stitch welded to ensure the structure is strong. This returns the frame to its original design strength. After installation the welds are ground down and the surface is prepared for bead blasting and painting.
Paint or Powdercoating Preparation
There are two methods for stripping the finish off the frame: media blasting and acid dipping. You must pick one before the frame is painted or powdercoated.
Bead blasting removes all the frame’s surface rust and some off the rust inside the frame rails.
Media blasting removes all rust and scaly paint on the outside off the frame. Tree bark is the media of choice because it does not pit the metal. The finished product looks as if it were covered with primer, but it is not. The bead blasting process only cleans the outside surfaces of the metal. Finished bead-blasted frames should be acid washed and oven dried before they are painted or powdercoated.
Heavily rusted frames or those that have had new sections welded into place should be acid dipped. Usually acid dipping is double the cost of bead blasting, but is a very advanced method for completely cleaning metal, such as a corroded Corvette frame. Most acid dipping shops use new products that are biodegradable. Few shops perform this work so you may have to do a little research to find one nearby. If one is not close you can ship your frame to them.
The correct process does not remove any metal, only corrosion, grease, and dirt. Because the acid is a liquid it covers all the inside and outside parts of the frame. When the acid dipping process is complete shops wash the frame with water to dissolve the acid. When the frame is returned, it with gloves to prevent body oils from rusting the exposed metal on the frame. If you decide to paint the frame or powdercoat it, find a shop that acid washes and bakes out the moisture before applying paint.
Powdercoating is my choice to protect the frame because it uses an electrical charge that applies a powder to cover all exposed metal. It is less prone to chip and peel and has proven to be very durable.
Powdercoating shops offer a wide variety of colors. When the powdercoating process is done, the frame has a high gloss or satin appearance. If you want an NCRS finish on the frame it should be lightly sanded and sprayed with the correct NCRS satin black paint to replicate the original finish.
Once a color is selected, the powdercoating shop uses high-pressure washers to remove any particles leftover from cleaning. The pressure washer is inserted into the box sections of the frame to remove any dirt or grease that may have been missed.
Once the washing is complete the frame is put into an oven for 10 minutes and baked at 400 degrees F until all of the moisture is removed. Next, the frame is horizontal mounted on a rolling rack, and pushed into a spray booth. inserts a vibrating tube into a large box of powder. Air hoses push the powder into a gun located in the spray booth. The operator applies the powder to the grounded frame with an electrically charged spray gun. The operator ensures that the powder is blown into all crevices on the frame.
Once the appropriate amount of powder has been applied, the rack is rolled into a high-temperature (400 degrees F) oven and baked for 10 minutes. After the is comple the frame is removed from the oven and placed into a cooldown area. After the frame cools it is carefully inspected to ensure it has no blemishes.
The finished frame is returned to the frame alignment rack to make sure no damage occurred during the cleaning and powdercoating process. Once it passes inspection it is ready for the owner to pick it up and begin the rebuilding process.
Written by Walt Thurn and Posted with Permission of CarTechBooks