First off, I want to say that I love the "Tech Corner" column. It helps us weekend warriors with our Corvette-project questions. Here's mine: I recently purchased a '97 Vette, and I've noticed an engine feedback noise through the factory radio. The noise is coming through the speakers on all stations, even when I have a tape in the player. It's become so annoying that I usually turn off the radio so I don't have to listen to it. What do you suggest?
It sounds like you're getting some Electro-magnetic Radio Frequency Interference (EMI or RFI). EMI/RFI can cause unwanted signals on a radio receiver or, in extreme cases, even result in driveability problems such as intermittent misfiring or a dramatic loss of power. Such problems arise when engine-management computers receive signals that have been altered by interference.
There are a few things that can cause this problem. The first thing to check is if there are any aftermarket electrical accessories installed in the car. Some non-factory components can cause the noise you're describing. To determine if a particular aftermarket component is your problem, unplug each item, one at a time, and see if the noise goes away.
The next thing to look for is non-factory ignition-system equipment. Aftermarket spark-plug wires are one of the more common offenders. Also, make sure your battery terminals are torqued to 11 lb-ft, and verify that the positive post of the battery is not leaking or loose. A loose battery connection can cause an array of electrical issues. The alternator connections should also be checked to ensure they're not loose.
If all of the above checks out, I'd recommend that a noise-suppression capacitor be installed into the main battery source that goes into your radio. The capacitor can be purchased from your local dealer or even Radio Shack. This should reduce or eliminate the condition.
I was just reading your recent article on the C4 headlight fix. It's applicable to the '89-'96 Corvette, but I have an '85 model, and the motor is completely different. Mine has two wheels, and I haven't been able to remove them. I'd appreciate any help you can give me.
You're correct: The headlamp motors on the '84-'87 Corvettes have a two-gear system that rotates the lamps. The problem is that the motors use nylon gears to rotate the heavy lamp assemblies, and the these gears eventually strip out where they contact a metal worm gear. This was a common failure on C4 Vettes, so Chevrolet redesigned the headlamp motor for the '88 model year.
The replacement procedure for the headlamp-motor gears is not very difficult and can be performed in about 45 minutes. The gear kits are available from most Corvette suppliers for less than $80.
1. First, remove the headlamp-housing retaining nut. Looking into the headlamp housing, toward the motor, and you'll see the 13mm retaining nut.
2. Next, remove the headlamp-motor wires from the headlamp frame. They're held by a metal retaining clip located in the corner of the frame. Now that the clip is removed, unplug the headlamp connector near the front side-marker light.
3. On the bottom of the headlamp motor, there's a knob with a locking strap. Remove the strap and rotate the knob until the headlamp is in a position where you can remove the side screw from headlamp-housing cover. Separate the cover from the housing, taking care not to scratch the paint.
4. There's a small bracket that attaches the headlamp motor to the hood hinge. Remove the carriage bolt between the bracket and the hinge. Next, remove the bolts that hold the headlamp motor to the headlamp frame. Now the motor can be removed.
5. Place the headlamp motor on a work bench and pull the wire clip away from the locking knob. Then, remove the Phillips-head screws that hold the motor housing together. At this point, you can separate the two components by gently prying them apart.
6. Using a pair of pliers, pull the large gear out of the motor housing. Note the placement of the small washers on each of the gear shafts; these will need to be reinstalled in the same location when the gears are replaced. Now, pull up on the gear; it will slip out. Wipe any crusty grease and old gear debris from the housing, apply a generous amount of lithium grease to the entire gear assembly, and install the new replacement gear in the motor housing in the same position from which it was removed.
7. To remove the small gear, you'll need to lock the shaft in a vise and use a brass punch and hammer to remove the pin that attaches the gear to the shaft. Once the pin is removed, you can take the shaft out of the vise and use pliers to remove the gear from the housing. Install the new replacement gear on the shaft, then put it back into the vise to reinstall the locking pin. Be sure to apply a generous amount of lithium grease to the gear teeth.
8. Before bolting the two halves back together, apply a small amount of silicone sealant to one of the halves to prevent water from entering and damaging the motor. Reassemble everything in the opposite order in which it was removed.
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