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C3 Bumper Cover Install - Rubber Bumper Blues

A Step-By-Step Replacement Of A Urethane Bumper Cover

John Pfanstiehl Mar 25, 2010
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If your Corvette was made in the last 38 years or so, it has a rubber bumper on both ends. OK, it's actually a urethane flexible bumper cover, but rubber bumper makes a better sounding title for the article. And even if your Corvette is pre-'73, your other cars almost certainly have rubber bumpers. So follow along to see what's involved with rubber bumper replacement, refinishing, and fitting.

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It amazed me that auto manufacturers almost universally changed to painted bumpers on cars. If I were a conspiracy enthusiast, I'd think the paint companies had a hand in this. Sure, those molded bumpers look pretty when new. They're sculpted and clean looking, and they blend into the bodylines. Plus, they were made to take a low-speed hit with no damage, right? Well, if it's just a small tap squarely with something very smooth, they might come away unblemished.

But most encounters are not so kind, and neither is time. If kept out of the elements, a steel bumper will be the same 10,000 years from now. By comparison, a rubber bumper will have aged within 10 years, and it may be severely arthritic well before the car becomes a classic.

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Replacement of the stock urethane bumper cover can be accomplished with basic hand tools. In fact, power tools won't even fit into most of the tight spaces you'll visit during this project. A yoga class would be of more help here. Corvette owners can choose both the parts and procedures to suit them. The pros and cons of stock urethane bumper covers and aftermarket fiberglass bumper covers are, well, covered. And the new bumper cover can be taken to a paint shop off the car as shown, or it can be installed first and the car driven to the shop. In any case, a handful of wrenches and a little patience can renew the look of a beat-up bumper.

Bumper Cover Options and Fitting
The original Corvette bumper covers were urethane and were very flexible. The flexibility was a necessity for bumper systems that could absorb minor impact without costly damage. The disadvantage was the wavy appearance of the cover, and in early years the dull finish that came from flex additives in the paint. To overcome those problems, aftermarket suppliers soon made fiberglass replacement bumper covers. Of course, the fiberglass covers are more rigid-and therefore are more likely to be damaged by a small impact-but they have the potential of being fitted to achieve a great appearance. Plus, the cost of fiberglass bumper covers is less than half the cost of urethane replacement covers.

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The advantages today of a replacement urethane bumper are originality, and possibly a better fit. The better fit is possible when only the bumper cover is being replaced, and no additional bodywork or repainting is being done on the adjoining body panels. The flexibility of the urethane cover provides a bit of wiggle room to push and pull the cover to fit the dimensions and angles of the top panels and fenders.

By comparison, a fiberglass cover has little give. If it doesn't closely match the body panels on your car, bodywork is needed. Grinding the bumper where it's too high or adding filler where it's too low. However, if bodywork and repainting is also being done on the top panel and fenders, then a fiberglass bumper cover has the potential of achieving a fit and appearance superior to a urethane bumper.

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In short, a replacement bumper cover will never fit perfectly without bodywork. However it may fit acceptably, or even fit better than the original bumper cover. The fit problem is due to variances in manufacture of both the body and the bumper cover. The bumper has to align with three different body surfaces: the top panel (upper surround) and both fenders. Not only are there differences in manufacture of each of these three parts, in the shark years the three panels are glued together, so there is significant variation in spacing between the panels, in their alignment and in the angles between them. Therefore, the same bumper cover may fit well on one car, but not fit well on other cars.

In addition to dimensional variations in the body, there will be dimensional variations in bumper covers as they are manufactured-even when they come from the same mold. Injection-molded parts are not perfectly identical. Small changes in temperature of the mold, temperature of the plastic, material variations, injection pressure, and cycle time all can make dimensional changes in the finished part.


Zip Products
Mechanicsville, VA 23111



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