'63-'67 Corvettes ( Midyear ) and '68-82 Corvettes ( Shark )
Brake pedal is spongy: This is probably the most popular complaint, especially on disc brake cars, and is almost always the result of air in the brake lines. Brake fluid does not compress ( at least not very much ), but air does. This explains why the brake pedal can move, but the brake pads don't react. Air can enter the brake system by many means, but the usual way is through the seals of the brake caliper piston. These seals surround the piston, forming a barrier that keeps the brake fluid in. If this seal is breached, an exchange happens. Brake fluid seeps out and is replaced with air. Early on, there is often no evidence of brake fluid leaking out. Small amounts will coat the back side of the brake pads, and may even be missed in a general inspection. With a small amount of brake fluid leaving the system, a small amount of air is entering. And that's all it takes. In more advanced cases, brake fluid will drip from the caliper, sometimes forming a wet spot on the floor when a car is in storage. We have seen cars with brake fluid streaked around the inner sidewall of the tire, indicating an advanced leak. Sometimes these leaks are the result of a failed seal, and other times due to corrosion of the cast iron caliper bore. Small pits in the bore will cause an irregular surface, making it impossible to seal. The solution that many aftermarket manufacturers are following, is to bore the caliper bores oversized and press in stainless steel sleeves. These sleeves will not corrode, thus preventing the problem of pitting.
But the caliper is not always the problem with the brake system. Lack of maintenance is definitely a close second. Brake fluid is hygroscopic, meaning it tends to absorb moisture from the air. This moisture will break down and lower the performance of the fluid, and corrode the inner walls of all the metal vessels of the brake system. Coupled with dirt, the brake fluid becomes something of a liquid sandpaper, eroding away all the seals of the master cylinder, wheels cylinders and calipers. We have seen Corvettes actually driven into our shop with master cylinders that have one reservoir completely dry, and the other looking something like the Mississippi river. We have seen brake lines that are so rusty, brake fluid is seeping out and leaving a wet spot. In the worst cases, we have seen wheel cylinders that haven't worked in so long that the pistons are seized, and the brake fluid has turned into a dry, sand-like consistency. In all of these cases, the cars were actually driven into our shop. And in all of these cases, the brake systems hadn't been looked at in a long, long time.
So what should be done? Every two years, have your brake system thoroughly checked. Have the brake fluid flushed out and replaced with new. Have your parking brake adjusted, and for owners of '63 and '64 Corvettes, have your drum brakes cleaned and adjusted. Lastly, have all steel lines and connections checked for any leaks or corrosion. Follow these guidelines, and your brakes will give you years and years of service.
Tachometer doesn't work: ( '62-'74 )Several conditions can enter into play when a tachometer fails to work, such as a broken cable, a failed tachometer head or a problem with the distributor. While the tachometer cable is the first thing we look at, more times than not the failure is due to stripped distributor gears. These distributor gears, as shown in this photo, consist of a worm gear that is "turned" into the distributor main shaft, and a side gear that drives the cable. The side gear meshes with the mainshaft gear perpendicularly, and is driven off the rotating mainshaft. Failure occurs when lubrication breaks down, and the gears wear through their hard outer layer. When this occurs, gear teeth wear away, or break off, and are rendered inoperable. Proper maintenance is the key longevity.
Parking brake doesn't work: This is such a common problem, and while it can be as simple as a cable adjustment, we're usually not that lucky. We have seen midyears and sharks that have had the parking brake shoes removed and then returned to the customer without parking brake shoes at all! Obviously, this "technician" wasn't savvy in the ways of spindle removal and setup. The spindle must be removed to properly and effectively rebuild the parking brake assembly. One of the parking brake hold-downs can't be replaced without removing the backing plate, which can't be removed without pulling the spindle Other examples have come to us with pieces of hold-downs and return springs laying in the bottom of the parking brake drum after rusting off. At The Restoration Station, it is our policy to do the job once and do it right. We replace parking brake assemblies with stainless steel shoes and hardware. These parts never rust, and likely won't wear out for a long, long time.
Speaking of Spindles: Here's a shot of a spindle with a failed outer bearing being pulled from a trailing arm. Notice the bearing's inner race (red arrow) still pressed onto the spindle, but the cage and rollers have broken away, and are within the trailing arm assembly on the other side of the seal. The cause: you guessed it - lack of lubrication.
The tops of my rear tires lean in: While this can be caused by spindle bearings that are excessively loose, the more common reason lies within the differential. Drive yokes in the differential turn the half shafts that drive your Corvette's rear wheels. These drive yokes are pushed inboard, to the center of the differential, by the weight of the car. In the center of the differential is a very large pin that keeps these yokes from moving " too far " inboard. Lubricant in the differential allows the yokes to turn against this pin without wearing either part - for a while. As the lubricant breaks down with age, and becomes mixed with positraction clutch dust, these parts start to wear through their outer hardness, then rapidly wear away. The photo shows a comparison of a good yoke next to a shorter, worn yoke. As the yokes wear, they move farther inboard. This causes the half shafts to also move inboard, which in turn causes the tops of the wheels to lean inward due to the weight of the car. At first you are simply wearing out the inner part of the tread of your tires, but later on, you're wearing out the differential housing. $$.
My car doesn't run well on today's gas : The 1990 upgrade to the Federal Clean Air Act has mandated the reformulation of gasoline as we know it. Today's gasoline is blended differently according to the season as well as the area of the country. It is more evaporative than ever, especially the cold weather blend with higher Reid Vapor Pressure. It has a lower boiling point, and contains replacement ( and corrosive ) oxygenates, such as ethanol ,since the phase-out of M.T.B.E. This is all aside from the fact that there is no more lead content in the fuel to ward off exhaust valve seat recession. Bottom line: Today's gasoline is not much like the gasoline your Corvette was designed to run on. The corrosive ethanol blends have an insatiable appetite for some of the elements of your fuel system, such as rubber, zinc plating in your fuel tank and the cadmium plating in your carburetor fuel bowl.
There isn't much we can do about the make-up of today's gasoline, but we can help it a little. First and foremost: If your Corvette is going to sit for an extended period of time, add fuel stabilizer to the tank. This will slow the negative effects of today's reformulated fuels. If your engine is stock, and doesn't have hardened exhaust seats or stellite-faced exhaust valves, it is susceptible to exhaust seat recession. Leaded racing gasoline as well as packaged Tetra-ethyl lead with a petroleum carrier are available from various vendors. The addition of these will give you similar results to pulling up to the pump in 1970. One thing to remember: Do not let these additives sit in your tank or carburetor bowl for extended periods of time. The addition of lead to today's gas doesn't seem to blend as it did in the 'old' days, and will tend to separate and clog carburetor jets or fuel injection nozzles if the car just sits for extended periods. Wean your fuel system off of these products before winter storage, and fill your tank with the highest octane pump gas you can get. Before you pull the cover over your car for a long winter's rest, add fuel stabilizer to the tank and run the car long enough to draw some into the carburetor. The best suggestion I can give to my clientele is not to put their cars up for the winter. Rather, run them periodically, or better yet, drive them when you can.
If your car has the original gas tank and has been in storage for more than 5 years, plan on replacing the gas tank, tank sender, pickup screen, fuel pump, and have the carburetor overhauled. In addition, your fuel lines will need to be flushed out, if not replaced. The fuel tank and sender, as shown in the photo at left, are standard fare for the restorations in our shop.
Headlights don't open fast enough, or not at all: ( '63 - '67 ) Can be a wiring problem or a faulty switch, but that's not what we usually see as the cause. Inside the headlight motor assembly is a small gearbox. This gearbox is what turns the high-speed spin of the headlight motor into the slower, stronger rotation of the headlight door. The armature of the motor makes up a worm gear, which in turn drives the small alloy gear shown in the photo. As the lubrication of the gearbox dries up, the alloy gear begins to wear until the teeth actually become deformed, as shown in the photo. This causes a binding condition that inhibits the operation of the gearbox, pulls extra amperage through the motor, heats wiring and connections and slows the headlight down, or stalls it completely. This is the cause, but the effects can be damaged wiring and switches due to extra amperage and heat buildup. At this point the entire system may need attention.
Wiper door doesn't work properly: ( '68 - '72 ) I could easily write a book on this one. This is one of the most troublesome assemblies to the applicable Corvettes, starting when they were still under General Motor's warranty. I have talked to people that worked on shark Corvettes when they were new, and have sited the wiper door as one of the most problematic assemblies. Still, it is quite an innovation in design and engineering, and you must admit that it is a great attribute to the Corvette when it is working properly.
The wiper door is comprised of two separate systems that work in harmony with each other. Boiled down to a basic explanation, the wiper switch completes an electrical circuit that closes the contacts of the wiper solenoid, enabling a vacuum path that moves the piston of the wiper door control valve, diverting vacuum to the wiper door actuator which opens the wiper door, which closes another electrical switch that completes the circuit to power the wiper motor. 1968 Corvettes take a different wiper motor and are wired differently, but the principles still apply. In this brief explanation alone, one can only imagine the combinations of problems that can occur. Diagnostics begin with the electrical system, and can be simply a matter of corroded connections. These connections may be in an outside harness, or internally in a relay. The wiper door relay is located beneath the radio in the center console. A faulty wiper solenoid, located behind the gauge cluster, will shut down the whole process as well. Here, one is tested on the bench. As the coil is energized in the relay, a vacuum circuit is enabled which takes the system to the next step.
The fact is, several electrical circuits don't work. If this is you, believe me, you're not alone. If you look at what happens to wiring that has carried current for 40 years, it's not hard to imagine that things can go wrong. The plastic resins in the insulation break down through out-gassing, and cracks form. Poor connections due to corrosion cause overheating of the wiring, turning plastic insulation to something more like petrified wood. You end up with a 12 volt supply line finding ground , and burning the harness like the photo at left. This is a shot of the back of an ignition switch of a '64 coupe, that was not only driven to our shop this way, but had a "complete" restoration prior to the current owner's purchase. The best solution, in any case, is to replace the wiring harness, as shown on a '66 gauge cluster at right.
Often times the electrical system is working properly and the problem lies within the vacuum system. This, of course, requires more diagnostics and testing. The main culprit and number one cause of failure in the vacuum system is the wiper door actuator. Seals within the canister fail, allowing vacuum to leak. With insufficient vacuum to work with, the inner diaphragm won't pull the actuator rod with enough force to open the wiper door. These actuators can be rebuilt, or most are available in reproduction.
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