The following list of common issues is intended for individual reference only, and may not reflect the specific issues of every 1970 Corvette. This information comes from a variety of sources including the NHTSA Defects Reports pages. While the intent of this page is to identify the common issues pertaining to the 1970 Corvette, it is not an all-inclusive list and should be used for reference only.
One of the common issues with the engines in a 1970 Corvette have nothing to do with any specific mechanical issues. The issue is that, more often than not, the original engine has been replaced, and the replacement engine is not the same type/model as was installed when the car was originally manufactured.
Overheating is a common problem on early C3 Corvettes. One of the most common causes of overheating is the replacement of the stock radiator fan and fan shroud with an electric fan.
CRANKCASE VENTILATION/PCV VALVE
PCV (Positive Crankcase Ventilation) Valves are important to proper engine operation. The PCV valve allows a pressure drop (vacuum) in the engine’s crankcase. In turn, this helps the engine piston rings seal against the cylinder wall. The PCV valve also acts as a check valve under hard acceleration when engine vacuum is zero. This allows the crankcase ventilation tube that is connected to the air cleaner to draw a vacuum in the crankcase when the throttle is wide open. PCV valves are often neglected but they play an important role in engine drivability and engine life. An improperly operating/damaged PCV valve can cause hesitation, poor idling, and stalling. The crankcase should never be totally closed- it will cause extreme oil usage and oil leaks Be cautious of replacing crankcase/valve covers with aftermarket brands that do not include baffles for the PCV Valve or crankcase tubes. Also, make sure that all PCV grommets are properly sealing to ensure that the proper pressures are maintained and that oil blow-by does not occur.
One of the common issues with the transmissions in a 1970 Corvette have nothing to do with mechanical issues. The issue is that, more often than not, the original transmission has been replaced, and the replacement transmission is not the same type/model as was originally installed when the car was manufactured.
The transmission vacuum modulator that controls shift timing could have a broken diaphragm allowing transmission fluid to be drawn into the engine. A minor vacuum modulator diaphragm leak will foul the number eight plug slowly and result in a minor loss of transmission fluid. A severe vacuum modulator diaphragm leak will create smoke out the tailpipe and noticeable transmission fluid loss. The number eight cylinder intake manifold runner is where the vacuum supply to the automatic transmission modulator is located. This number eight intake manifold runner also supplies the headlamp actuator system. Therefore, this vacuum supply can create a very rough idle if both systems were leaking. Many times the fitting that screws into the intake manifold is loose.
Both the driver and passenger door windows are known to fail. There are generally two conditions which cause the window to stop operating: 1.) A blown fuse or defective relay, or, 2.) A failed power window motor. When inspecting the vehicle for a cause, always check the fuse first. The replacement of a power window motor is a time consuming process requiring access to the inner workings of the door via removal of the inner door panel.
In instances where the window fails to go up completely, inspect the window gear regulator. If any of the gear teeth are missing from the widow regulator, the gear will need to be replaced. If the teeth on the regulator gear are not damaged, the window motor will need to be removed from the regulator and inspected. A damaged worm gear (gear drive on the window motor) will require replacement of the entire window motor.
If the window rattles when the vehicle door is closed, inspect both the window regulator mounting bracket (which may be damaged/broken), and the window anti-rattle cushions. Due to age, the window cushions can become damaged or may fall off the vehicle. Fortunately they can be easily replaced at many auto parts stores.
If the window travels excessively fast during operation, inspect the power window spring. A broken spring can result in costly repairs to the to the power window motor or the window regulator gear.
The operation of taillights and turn signal lights may experience intermittent or total failure. Although there are a number of possible causes for this issue, the most common cause of failure is a bad ground in the taillight circuit. When troubleshooting, check for breaks in wiring and check for wiring grounds. Other possible causes for failure include bad lightbulbs, bad turn signal switch, and/or bad brakelight switch.
Depending on the climate and driving conditions, the 1970 Corvette is known to develop extensive corrosion/rust in a number of areas including the frame and the "bird cage". On the frame, the most common areas where rust is known to develop include just forward of the rear wheels, the front cross member, the framework around the doors and the windshield pillars (the area known as the aforementioned "bird cage.") One of the tell-tale signs of a rust/corrosion issue is the presence of dampness/wetness on the forward floor areas. Severe corrosion may also resort in door sag and can adversely affect door alignment, resulting in a large (and increasing) gap between the top of the door and the fender.
HEADLAMP ACTUATOR VACUUM LEAKS
All Corvettes from 1968-1981 can have a large vacuum leak from the headlight actuator vacuum system that will affect the engine idle. When experiencing rough idle, remove the vacuum hose and plug the fitting temporarily, then check engine performance. See Transmission Modulator Vacuum Leaks above for additional information.
The rubber hoses and other components of the headlight vacuum system are known to wear out. In many instances, only one of the headlight assemblies will operate. Always check all rubber vacuum lines when even a single headlight assembly is not operating properly as many times, it the result of a failed or collapsed line.
Over time, the door hinges on all C3 Corvettes fatigue and begin to fail, causing the doors to sag and other alignment issues including broken door seals, water leaks, and road noise. To prolong the hinge life, lubricate the hinges regularly. In the event that the hinges do sag, replacing the hinge bushings and pin is also an option, although replacing the upper hinge pin will require the removal of the dashboard speedometer cluster.
DISCLAIMER: While Corvsport.com makes every effort to ensure that this information is complete and accurate, you should always consult the manufacturer of your vehicle if you have a specific issue or question.