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Corvette FAQ

Old 01-09-2005, 05:57 PM
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I am planning on changing my tranny fluid and clutch fluid this week. Do I go with synthetics or stock oil for my 99 FRC? My M6 is unmodified other than the clutch.
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Old 01-09-2005, 06:09 PM
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Eugene, we all appreciate your hard work. I'll try to keep this updated as you updated the FAQ over there. Just let me know when there are major revisions.

Thanks again for all your work on this...
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Old 01-10-2005, 07:20 PM
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Wow,that's an enormous amount of info.Thanks
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Old 01-15-2005, 07:48 PM
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Old 11-16-2005, 04:21 AM
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Wow thanks for all the help.
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Old 05-09-2006, 03:20 PM
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More from Eugene... (He's the man)!!!

Common Problems

Leaking Battery
Many C5's came with AC Delco Freedom batteries that tend to have the case crack near the battery posts. The leaking battery acid would drip down the side of the battery, down the funnel-like battery support, straight down onto the PCM and the wiring loom. It can also get onto the A/C lines. I believe they are the vacuum lines that control the movement of the interior vents, and usually the system will default to blowing out the defroster vent. Sometimes car crippling damage would occur, sometimes not. It worst it would mean replacing the battery, the PCM, the wiring harness, grinding the rust off the frame to repaint it, changing the A/C lines and possibly swapping out another computer as well. This mostly happened on early C5ís because later C5ís used a gel-type battery that cannot leak, but I believe the problem resurfaced on í04 or í05 models again.

Check this out before buying a C5. Use a 8 mm monkey wrench, preferably a ratcheting closed-end version, to removed the battery cables. You also remove a holding block on the front side of the battery. You will need a long extension to reach it. The battery lifts out, then remove the black plastic battery tray. Look under the tray for rust or white powder--signs of evidence of battery acid damage. It would probably be best to move to the next Vette unless you don't mind possibly tackling this repair in the future. It's possible that the car will throw codes for no apparent reason.

No matter what Vette you buy, replace the battery with a gel-type battery, like the Optima Redtop, sold at CostCo for $100.

Grounding Problems aka CRAZY electrical gremlins!
Bill Curlee has a great thread on the problems that corroded ground connections can create, and how to clean out the grounds. The most problematic ground connections are behind the headlights on both sides. Check out Billís thread for detailed info: Go!
Hereís where all the grounds are: Go!

Water Intrusion
Water leaks have several ways of getting in the car, and none of them AFAIK are very difficult to fix. Proper adjustments and maintenance will prevent most leaks.
Bill Curleeís thread abouting locating & cleaning the udders, and sealing the door hinges.
Hereís a few TSBís from the
1997-1998: Service Bulletin: Waterleak Above Door Glass (Reseal Blowout Clip)
1997-2002: Service Bulletin: General Waterleak Guide
1997: Service Bulletin: Water Drips into Rear Compartment After Hatch/Glass Has Been Opened

Corvette seats are delicate. Sliding hard across the bolster can break it, causing it to flap side-to-side. The leather is cheap, and there's little protection for it. It will wear out and form cracks, which is normalÖfor cheap leather.

The wire springs in the seat bottom, and the bars in the bolsters can also wear thru the foam and leather, but that can be fixed by placing layer of burlap between the springs and the foam.

Check the black plastic surround on the bottom of the seat to make sure it fits snugly against the leather, and isn't cracked. Older style plastic surrounds had a tendency to separate from the seat, but could be pushed back in. The newer style plastic surrounds can be used as a direct replacement, but one of the plastic studs may need to be ground off, or a hole will need to get punched into the leather.

The seats tend to rock back and forth by about a 1/4" during acceleration and braking. It can be fixed, but GM will not fix it. Some lucky owners can get the dealer to replace the frame under warranty. The seat backs swinging forward under braking is normal, and not considered a problem.

Here are a couple fixes: --- must be a member
Rocking Seat Fix

Seat choice
Get the sport seats. The sport seats have a hole under the headrest. Some people put racing harness belts thru those loops. The seat frames and foam in both seats are interchangeable. Harness belt holes can be installed using Ford harness cutouts. Ask the dealership for them, they should know what it is without a part #. The foam in a standard seat will need to be cut, and sewing will have to be done, but itís an easy job.

Headlight bezel plugs
There are 1-1/2" plugs that are located on the headlight bezels that would fall off on the older Vette's. The new style plugs, have a twist-lock to prevent them from falling out, but also requires new bezels. Only the new bezels & plugs are available now, and they are compatible with older C5ís.

Headlight gears
The gears in the headlight motor are plastic, and wear out over time. Ice, heavy Euro or projector headlights and twilight sentinal will cause the gears to wear out quickly. Fortunately a few years ago, Rodney started selling replacement brass gears, check out his website. Corvette America and probably a few other vendors now sell their own copy of his brass gears. Hereís a thread that shows how to replace the gears.

Replacement nylon gears are also available from Motormite Help!, part #42400 for $10-13. Src

To replace:

Torque Settings
All Data Diy
Headlamp Mounting Bolts 20 N.m (15 lb ft)
Headlamp Mounting Nuts 10 N.m (89 lb in)
Headlamp Bezel Retaining Screws 1.9 N.m (17 lb in)
Headlamp Capsule Retaining Screws 3.5 N.m (31 lb in)
Headlamp Intermediate Bracket Screws 1.9 N.m (17 lb in)
Headlamp Opening Door Screws 1.9 N.m (17 lb in)

Roof noises
If you buy a coupe with a removable roof, you can expect wind noise and some creaking. The wind noise will never totally go away, but if there's creaking, you can eliminate that by thinly applying dielectric silicone grease to the weather-stripping. It also prevents cracking, so do this to all weather-stripping, on any car.

Hood rattles
During cold weather the rubber hood stops can also rub and rattle against the hood. Adjust and lubricate the rubber stops so when you pull the corner of the hood up, it doesnít pull up, but the hood still closes.

Drivetrain rattling
The valvetrain makes a significant amount of noise at idle. It may sound like sewing machine. Converting the valve rockers to true shaft-mounted adjustable roller rockers with may help eliminate the valvetrain noise if adjusted properly. Installing a big cam and stiffer valve springs will make the noise louder.

On manual transmission cars (M6 or M12), the transmission sounds like it is rattling when leaving the line. It is normal. It is the clutch throwout bearing rattling around. Sometimes you'll hear a horrible rattle if you shut off the engine. If you press the clutch pedal in while shutting off the car, you won't hear it.

Shaky breaking
The front brake rotors warp easily under heavy brakingÖor at least thatís what uneducated drivers think. I tend to believe StopTech:

I verified this by lightly grinding my rotors with steel wool. Garnet paper is recommended, but I havenít tried it.

If you insist the problem is warping, donít turn the rotors since thinner rotors warp more easily. Resurfacing the rotors is only a temporary fix, one that is less effective each time your resurface the rotors due to the reduced thermal capacity of the rotors. Rotors are available for $25 at Napa and RockAuto.

Scraped front ends and rocker panels
Checking for scrapes is an easy way to tell if the car was treated well. It's almost impossible not to scrape the front end, but there are two metal crash bar loops that should prevent the bumper from scraping. The bumper itself should not have scrape marks on it. Check the underside of the tip of the bumper, and the bottom corners of the bumper. If the crash bar gets scraped enough, eventually it will wear down to the point where it needs to get replaced. It costs about $220 for the crash bar, nut-serts, bolts and insulators, and can be replaced in a couple of hours, just be sure to hook the hoses and electric connector back to the A.I.R. pump.
Hereís a list of ALL the parts youíll need to replace the impact bar and the side air deflectors:
Part #------Qty---Description
10188023---001---Insulator (goes to bottom of radiator)
10278679---001---Insulator (goes to bottom of radiator)
10400765---001---Plate (the actual impact bar, unpainted)
10419312---001---Panel (air deflector)
10419313---001---Panel (air deflector)
Not all of these parts need to get replaced, and there will be a few leftovers, but it will get the job done.
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Old 05-09-2006, 04:00 PM
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A & A Corvettes invented two products to prevent damage from both kinds of scraping. They have wheels that attach to the crash bar, allowing the car to roll on driveways instead of wearing down the crash bar. It will still scrape the spoiler, but the spoiler is a cheap wear item that takes only 2 minutes to replace without a lift or jack. They also make two aluminum strips that attached the frame next to the rocker panels, and they take the scrapes themselves instead of the rockers panels. Neither of the devices are visible unless looking under the car, and they are discreet enough to possibly be missed anyway. If you see these devices installed, you can be pretty sure the owner took good care of the car. Without this extra protection, you can expect to replace the crash bar and repair the rockers several times over the life of the car. WARNING: It wonít stop all scraping damage, just reduce the possibility of it happening, and reduce the damage when it does happen. Low hanging headers will probably still scrape.

Hood seal weather-strip
The sides and back of the hood compartment have weather-strip installed from the factory. The front is left open. Many owners install weather-strip along this front edge. You may not even notice it since it looks identical to rest of the weather-stripping. This extra weather-strip helps keep the engine compartment clean, and may also help the air intake system work better. This is another sign that the owner took good care of the car. The engine compartment stays pretty clean, but this the "extra step".

A/C System
There are two kinds of climate controls. One is manual with *****, and the other is a dual-zone electronic system. The dual-zone system did cost more, but is not as reliable as the manual system. A leaking battery can affect both systems; a symptom is when the vents cannot be switched.

Over time, and especially in humid climates, condensation can leak onto the passenger side carpet. There are 3 udders under the driverís side cowl, and behind the battery. There are slits on the bottom--vigorously squeeze and massage the udders until free of debris.

If the vent settings cannot be changed, the vacuum line is probably loose, clogged or broken. Read more!

Squeaky steering wheel
When you turn the steering wheel, you may hear a squeak. It's just the plastic surfaces rubbing against each other. A shot of lubricant fixes this.

Squeaky/chirping/grinding wheel bearings
Drive slowly, better yet, coast along at low speeds with the windows open in a quiet location. Listen for a squeak from the wheels. Try turning in different directions. If you hear the rear wheels squeaking, you may have a worn wheel bearing. A replacement bearing costs $600 list, but you can usually find it for $400-450. I've heard that AutoZone has a better replacement for $126 by a company named Timken. The part is easy to replace if you can separate the ball joints; I bought the Kent-Moore tool to do mine. The problem may persist safely for a few months, but eventually will become annoying. It seems to be a common problem, and more so for the rear wheel bearing. I've never heard of it happening twice to the same car, so if you fix it once, you're probably good for life. Several racers replace their wheel bearing every year.

A broken emergency drum clip may cause a false diagnosis. Be careful when removing & replacing the rear rotors.

Oil woes
Many late 2000 thru 2001 Vette's burn a lot of oil when the engine is kept constantly over 4,000 rpm's. This is caused by ring flutter, which allows extra oil to seep past the oil control rings, but doesn't seem to cause any extra wear to the engine. Chevrolet has rebuilt and replaced engines for owners that complained about excessive oil consumption. Their policy is that while the engine isn't normally operated like that outside of racing, it is the owner's prerogative to drive around in second gear all the time if they want to. It is covered under the warranty.

The PCV system also has a tendency to suck oil back into the intake at high rpm's. It doesn't seem to cause any problems, other than a slight mess inside the intake manifold. The newer style PCV system can be installed, but this requires removing all the components in the top of the engine valley. Usually only racer's bother with the hassle. Several generations of PCV systems have had the problem, and at this time, December 2004, the PCV system still sucks oil into the intake.

The oil-sucking problem will cause carbon buildup in the cylinders. The dealership sells GM Top End Cleaner, and Napa sells SeaFoam. The Top End Cleaner is not available in some smog states like California. Run a tube from the bottle into the hole for the PCV system behind the throttle body on the passenger side. Start the car, then start slowly sucking the solution into the engine. Donít go too fast or the engine could lockup. As soon as the solution is gone, stop the motor for >4 hours, but preferably 12 hours. Be aware that when the engine is restarted, there will be a LOT of smoke!

The oil-sucking can be prevented by installing a catch can. AMW and Greddy make catch cans, but a homebuilt catch can may be built using a Campbell-Hausfield air tool oil separator from most tool stores, including AutoZone. The AMW and Greddy cans are ~$100, but look great. The CH can is $15-25 for all the parts, and you can see how much oil is in it.

Overheating & burning smells
Even though the engine can heat up to 220, even 240 degrees Fahrenheit, this is normal. The radiator will keep the engine cool enough unless the radiator is blocked. Reprogramming the PCM can allow the fans to turn on earlier. If the fans also cool an aftermarket oil cooler, make sure the oil occasionally gets to 220 degrees to allow condensation and fuel to evaporate away. Fan settings and oil thermostats are two different ways to do this.

It's not uncommon for plastic bags to get sucked up under the front bumper, and cover the radiator, thus causing the car to truly overheat. If this happens, take a quick peek under the bumper, and remove anything under there. Sometimes bags get stuck to the exhaust pipes too, causing quite a stench as they burn away.

Locked steering column
All C5ís, particularly manual transmission C5ís, and early C6 steering columns have a tendency to lock and stay locked. Usually it can be unlocked once, but just once. Some owners claim that vigorously shaking the steering wheel can unlock the steering wheel. Dealer's are able to disable the locking mechanism with a modified locking plate. Currently this is the only real method to disable the locking mechanism. Basically the wheel will still try to lock, but there will be nothing for it to lock to. Itís like a door dead bolt with a slot cut into the door jamb. There is a $100 kit that disables the steering column lock, and can be installed easily, but enough car vibrations can cause the lock to fall into the locking plate, even while driving!

GM has a part (#88952428 or 88952428) that has a harness wiring jumper and different lock plate. Not sure what the difference in the kits are.

After reading a few posts, manual transmission C5ís & C6ís are still in danger, even if the lock is disabled. The lock can vibrate out over time and get trapped in the locking plate. Auto transmission cars that have undergone the recall and new autoís will not have the locking plate at all, so they are safe. More information about COMPLETELY disabling the steering column lock will be forthcoming from otherís on the forum, and by my own personal project. Until then, here are a few links about the topic:
Column Lock Harness K Installation
A4 non locking column plate --- must be a member
Column-lock again even with CLB!
Has anyone ELSE beat column lock?

Faulty gas gauge
If you have bad gas (phew!), the fuel sender can be affected by the high sulfur content in the fuel, and cause the gauge to read empty. They car will still operate normally, and the gas gauge will work again if you use better gas, and will usually start again when you restart the car. It's just better to use good gas. Some people have had luck with running fuel filter cleaners thru the gas tank. New fuel senders sometimes fixes this problem. This thread has a LOT of ideas about what could be causing the problems, how to avoid problems, and how to fix it. It also points out how the late C5 fuel tanks and crossover tube is different.

Noisy fuel pump
There are two fuel tanks, and two fuel pumps. One fuel pump continually pumps gas from the passenger side tank into the driver side tank, and is quiet. The main fuel pump is directly behind the drivers seat, and can be annoying loud, especially on early C5ís. It's normal, and not a sign of a failing fuel pump. Chevrolet does have a bulletin out instructing how to better insulate against the sound of the fuel pump. This is merely an annoyance. A newer, quieter pump can also be installed.
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Old 05-09-2006, 04:00 PM
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Extremely high oil pressure reading
The oil pressure sensor can fail, but it is still okay to drive. Turn the car off, but with the key in the ďonĒ position and check the oil pressure gauge. It should read ď0Ē. If the oil pressure sensor is bad, it will show a positive reading. The oil pressure sender is located behind the intake manifold, and will require moving the intake manifold. The sender costs about $40 and part # 12573107 or 12562230.

Suspension squeaking
In cold weather you may hear the suspension creak when you go over speed bumps. To fix this, clean (optional) and lubricate the sway bar bushings. The adjustable metal sway bar end links on Hotchkis and T1 bars can also create loud clicking sounds. Most adjustable end links are quiet initially, but wear out and get noisy over time. Greasing and protecting the end links from dirt may prevent wear.

Tough shifting
The shifter in manually shifted Corvette's takes a strong arm to get it into gear. You really have to make sure that the shifter is fully in 1st and Reverse, or it will pop out of gear when you let the clutch out. This is not the fault of the car, but the fault of the driver.

Manual transmissions -- Replacing the transmission fluid often helps shifting. Early transmissions have paper blocker ring that require Dexron III compatible (usually organic) fluid because some synthetics will destroy the paper blocker rings and subsequently the transmission. Later transmissions, and all rebuilt transmissions, have Kevlar/carbon fiber parts that allow the use of synthetic fluids. I believe the 98-00 transmissions have the paper blocker rings. The safe transmission fluids seem to be: GM Synchromesh PN #12345349, Honda ATF-Z1, Royal Purple Synchromax, Amsoil ATF, OíReilly Dexron III ATF. The following transmission fluids may be unsafe for early transmissions: Redline D4 ATF, Mobil 1 ATF, Royal Purple Max ATF.
Related threads: - Ending the speculation: Blocker rings, who's had them fail? - Ending the speculation: Blocker rings, who's had them fail?
Mobil 1 Synthetic ATF for a M6?

If it is especially tough to shift into 2nd or 4th gear, it's possible that the synchro's are worn out or the forks are bent. Do NOT force it into gear. Abuse creates and aggravates this problem. You can still drive, even quite well, without synchro's....or a clutch for that matter if you know how to rev match.

Some aftermarket shifters make it easier to make sure you're fully in gear, and prevent gear grinding, but they also vibrate, and require more effort to shift. The stock shifter has a tuned weight damper that changes the vibrations to a non-audible frequency. The shaking doesnít annoy some people, and there are some fixes.

Leaky butt
The differential can leak from the side covers. The problem has to do with the design. The lip on the casing is not wide enough to create a proper seal with the cover. Resealing the covers can be successful, but many dealers do not use the correct sealant.

Inside/outside tire spinning
If one tire spins while turning, adjust the friction modifier ratio. Aftermarket gear fluid from Royal Purple, Amsoil and Redline do not require additional friction modifier. GMís friction modifier is PN #12377916. Too much friction modifier and the inside tire will spin/skip/hop. Too little friction modifier and the outside tire will spin/skip/hop. -- Thanks Russ!

Tire hop
Tire hop during hard acceleration in cold weather is common, even if the same tires donít hop in warmer weather. Tire rubber when viewed thru a microscope looks like a web. Normally parts of this web grabs onto objects on the ground and stretch until either the car moves forward, or the web breaks, resulting in tire spin. I believe in cold weather, the web is too stiff for either of these events to occur, so the tires hop. To find out more, read Racing & High Performance Tire: Using Tires to Tune for Grip and Balance. I havenít read it, but if you do, please let me know if my guess is correct. I found a couple stories on Google about people curing wheel hop with stiffer bushings and/or (jounce) shocks.

Interior rattles
The visors may rattle when they are put up, but if you flip them down, the rattle goes away. Squeezing the mirror lid down seems to take care of it. Try glueing a piece of felt or velcro between the mirror and lid to see if that fixes it. Caravaggio also makes replacement leather visors, but they go for $400.

The stereo is Bose, and to go along with the historically crappy build quality of Bose products, Bose has graced the Corvette with Bose emblems on the door speaker covers that rattle when you play music with bass. A Bose system doesn't exist that puts out good bass, but the system still manages to rattle the emblems when playing Country, Hip Hop, or Techno at moderate volumes. Check this problem by having a passenger and yourself putting a finger on the emblems with music playing. Glue the emblems down to fix it.

If the roof isn't tightened down enough, it will rattle. There are some adjustment screws in the roof to make this adjustment.

Belt Chirping
During cold weather, the belt can chirp. Goodyear Gatorback belts from AutoZone donít chirp.

Sticky Hatch
During cold weather, the hatch may pop up slowly, or not at all. Spray the latches with silicone grease until they come up properly. If the struts do not hold up the hatch, try lubing the strut bars.
1997: Service Bulletin: Hatch Will Not Pop Up When Activated in Cold Weather

Rocker failure
The needle bearings in the OEM rockers have been known to fail. Usually the problem is noticed with extra valvetrain noise and needle bearings stuck to a magnetic oil plug. Nasty Performance will rebuild OEM rockers with Harland Sharp bearings. This seems to be one of the better solutions since the stock rocker is very good at high rpms. Most aftermarket rockers are nose heavy and require grinding the heads and valve covers to fit. Currently Harland Sharp rockers are having problems with c-clip retainers falling off and causing problems on the way. Iíll be following this issue since I have a set of HS rockers on my shelf waiting for this issue to be resolved. Here are some links:
LS1Tech - Harland Sharp Rocker Failure
LS1Tech - Install or not install HS rockers?
1998-2002: Service Bulletin: Needle Bearings Found In Oil Pan (Replace Rocker Arms)
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Old 05-23-2007, 10:06 PM
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Blinkers / Indicators / Turn Signals cut out intermittently while driving...
If while driving your turn signals mysteriously cease to function / cut out intermittently for a period of time--and then return just as mysteriously--you may need to replace your Hazzard switch. The turn signals run through the Hazzard switch, which can overheat over time and damage the internals of this component. The Hazzard switch is a $40 part from gmpartsdirect that can be replaced by the do-it-yourself'er with a little careful maneuvering and some small hands, much the same way you would replace the radio in your C5.

Read below for a detailed write-up / instructions on how to change the C5 Hazzard switch and to find the Part #:

C5 Hazzard Switch Replacement
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Old 08-08-2007, 09:51 AM
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FRC and z06s are Less aerodynamic? i always thought the opposite
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Old 06-27-2009, 09:24 PM
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Default c6 ?

This is awsome info, does anyone have the same type of info on the c6?
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Old 07-12-2009, 04:19 PM
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Great data.
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Old 03-02-2011, 12:51 PM
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Eugene has also created a webpage that he is maintaing with this information The C5/C6 bible. The URL to that webpage is
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Old 03-02-2011, 04:30 PM
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Originally Posted by J-Rod View Post
Eugene has also created a webpage that he is maintaing with this information The C5/C6 bible. The URL to that webpage is
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