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C3 Corvette Fender Flares - Open Wide
Creating Custom Fender Flares For The C3
May 28, 2009
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C3 Corvette Fender Flares - Open Wide
A few position lines were drawn radially through from the fender lip to the quarter to aid alignment later, and the outer fender was cut along the marked line with a cut-off wheel in an air-powered die grinder.
While making the cuts, it is important to be aware of the double walled and flange-bonded area in the lower wheelhouse. We cut the inner wall flush and then removed the outer wheel lip section.
Since the fender flare will be bonded inside and out, the inner wheelhouse needs to be ground and cleaned so any fiberglass work in here will adhere. We cleaned to an area of about three inches all around the inside of the cut to bare fiberglass.
A set of five steel brackets were formed to bolt the wheel lip back in at a new location, spaced out from the original position. The lip was moved out 1.250-inch at the top center, about .850-inch at the front bottom, and .950-inch at rear bottom. This positioning subtly tips the edge out more at the top center, and allows a gentle sweep off the door edge outward.
The metal brackets were made of thin flat sheet metal, so they can be bent to a curve and screwed through the body at the quarter and the fender lips. The brackets were slotted at the mounting hole to allow adjustment in or out.
A simple wire gage is used to make a line of sight determination of the height of the relocated wheel lip, which can be adjusted by the curve of the mounting brackets. Our final position was just slightly raised from stock (about 1/8-inch). Since the lip is spaced out, the radius of curvature of the lip will no longer meet the quarter, and given the original angle of the lip, the joint needed to go up about as much as out, so a tape line was set at 1.25 up off the quarter cut, and tapering slightly to the sides.
Once the final position was set and locked-down with the brackets, the quarter and wheel lips were cut again. The wheel lip was cut to remove the radiused part, leaving about 1/2-inch, tapering out to just the lip edge at the front. The position was already set with the brackets, since removing this material loses the position reference.
Here we have the quarter after most of the cutting. The area between the lips and the quarters will be fabricated to create the new flared fenders.
To ensure a good bond, the edges of the original fiberglass were roughed with a carbide bit to bare fiberglass.
The next step was to build a mold from the inside. We began with a layer of really heavy-duty and sticky duct tape, tightly laid in strips from the inside.
To add strength and form to the mold, thin cardboard sheets were cut in sections and fitted onto the sticky side of the tape from the top. The mold was made very precisely, using paper patterns for the cardboard to fit together along the joint, edge-to-edge, without overlap, like a puzzle. The ideal was to gain full purchase on the edge when the fiberglass goes in later, and near perfect shape when the'glass cured.
Since the fiberglass will bond to our cardboard mold, it was covered with vinyl tape so that it can be removed once the 'glass cured. The top tape layer tucked a fraction of an inch under the cut edges at the wheel lips and quarter, leaving the cut edge fully exposed.
Next, the fiberglass was laid over the temporary mold; it took about 5-6 layers to equal the thickness of the original material and sit flush, then another layer on top just overlapping both sides a little for strength.
The finished fiberglass work showed a very accurate net shape for our revised fender. After the 'glass cured, the mold and bracing brackets were removed and the seams were overlapped with 'glass from the inside, providing full strength to the bridge section of the flare.
A D/A air sander with #40-grit discs was used to rough-finish to raw fiberglass. We sanded back any high spots until the entire surface was a smooth flowing curve.
A layer of Mar Glass reinforced filler was used next to fill and smooth the flare. It is best to apply the material in one clean continuous wipe.
We worked the Mar Glass with a body file before it reached full hardness. One layer was enough to get the shape nearly perfect.
Once the Mar Glass reached full hardness, the rough filed surface was smoothed by sanding with relatively coarse #40-grit paper on a sanding block.
Reinforced filler like Mar Glass cannot be worked to a perfectly smooth and fine finish. To take our new flare to this level, we gave the entire surface a thin wipe of filler, and block sanded with #80-grit, followed by #180-grit paper.
Once sanded and sprayed with a coat of primer, the new flare looked great. We achieved our goal of retaining the original character of the fender line, while providing for substantially increased tire clearance.
From the front, we were quite pleased with the nice tapered flow of the flare from the door seam out to the fender lip. This is an area where many flare designs can look rather abrupt as the fender line moves outward.
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