C3 Corvette Bumper Repair - Rubber Revamp

Simple Fixes For Factory Urethane Bumper Caps

Steve Dulcich Mar 11, 2010 0 Comment(s)
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Our '76 shark is fitted from the factory with urethane bumper covers. While 30 years of service is commendable, the battle scars were evident. The worst of it was the right corner, which showed evidence of cracking from a minor impact.

One of the defining characteristics of the later C3 Corvettes is the molded bumper cover. In fact, the move away from traditional chrome in favor of molded urethane proved to be a major change, one that resulted in many enthusiasts differentiating C3 production by only this change. While the earlier chrome bumper cars now have a definite edge in collector value, the later rubber bumper cars may just have an advantage in enthusiast value. After all, considering the spectrum of classic cars, these later C3s are an amazing bargain, and the less-than-iconic status opens the door for unapologetic modifications.

Urethane bumper covers came into existence to meet the requirements of federally-mandated impact standards. The flexible material was actually a cosmetic cap that covered an impact-absorbing structure underneath. Today, this system is nearly universal, but when introduced on the nose of the '73 Corvette, it was much more a novelty. While other manufacturers were applying the chrome and steel approximations of railroad ties under the nose to meet the standards, the Corvette's rubber bumpers were amazingly sleek. In 1974, the Corvette received a similar system at the rear, and this was carried out to the end of C3 production.

The urethane was not without its flaws. By nature, the material is flexible, reportedly to allow the caps to conform to the body structure and shape during installation. This allowed the cap to be fitted to match the curves of the body, while accommodating minor production variations. Though the life of the factory bumper covers proved to be exceptional, it is not uncommon for cracks to develop, particularly in older covers that have been subjected to minor impacts.

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Our plan was to repair the cracks, and repaint the upper and leading surfaces of the original covers. Repairing the cracks begins with "V-ing" out the damaged area along the length of the crack. This gives the repair compound a broader surface area to grab, which will result in a stronger repair. We used a carbide burr, though a grinder or even sanding can accomplish the same effect.

Such was the case with our '76 shark. Although the overall cosmetics were in acceptable driver condition, the front bumper cover was showing definite signs of age. The worst of the maladies were noticeable cracks at the right corner, damage obviously caused by a minor impact. The cover on our car also exhibited the waviness that is an unfortunate result of the urethane material's flexibility.

We have defined long-term plans for this machine, including some body modifications and, eventually, a complete paint job. At that later stage of the game, our direction will be to replace the flexible urethane bumper covers with hard fiberglass, and blend the covers into a seamless, flowing continuation of the body. At this stage, our goal was simply to address the most egregious problems without removing the cover from the car. The covers are retained by multiple fasteners and retaining strips, which are subject to corrosion. Experience has taught us that attempting to remove these covers might as well lead to replacing them, since the fastener kit will likely need to be replaced, and the covers can be further damaged in the removal process.

We carried out some sound repair processes on our damaged front bumper cover and were pleased with the results. We were able to greatly improve the look of our Corvette in about a weekend's time and for a minimal cash outlay. While the soft urethane cap will never provide perfection of form, this rubber-bumper car will look much better when it's coming at you.

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