from the editors of:
GM High Tech Performance
LOG IN / SIGN UP
GET THE MAGAZINE
tech & how to
engines & drivetrain
Chassis & Suspension
paint & body
Best of the Best
GM High Tech Performance
C3 Bumper Cover Install - Rubber Bumper Blues
A Step-By-Step Replacement Of A Urethane Bumper Cover
Mar 25, 2010
View Full Gallery
View Full Article »
VIEW FULL GALLERY
C3 Bumper Cover Install - Rubber Bumper Blues
Cracks in the paint are never a welcome sight, and they are all too common on rubber bumpers. These occurred after this car rolled into another at about zero miles an hour while waiting at a stoplight. Notice there are not even any scuffs or chips at the point of contact. Before considering repainting bumper damage like this, inspect the rubber under the paint. If it's cracked, a new bumper cover is the best long-term solution.
After baking in the Florida sun, this bumper cover cracked, split, and popped apart. Hard to believe but true, this was not the result of a collision. It happened spontaneously while sitting out in the sun for a few hours after being washed.
The cover still felt flexible to the touch, even though it was at the end of its useful life. This shows why it's wise to make sure the bumper is not brittle before spending money on repairs or refinishing.
The new urethane bumper cover from Zip came well protected. The new cover was made from the factory molds and uses a more advanced urethane compound that is less likely to sag and wrinkle as it ages. Fiberglass covers are another option and are described in the accompanying sidebar.
The exterior surface finish on the urethane cover was excellent. There were no pits, sand scratches, or blemishes. The mold flashing was well trimmed, and the exterior surfaces were primed.
Order the upper retainer, and both left and right side retainers for the bumper cover. Most Corvette owners think their car is rare, but it would be really rare if the old retainers were still in good shape after decades exposed to the elements.
The studs can become loose in the upper retainer strip, just like the originals. JB Weld cured the problem. Trim any cement after it dries because the retainer fits tightly against the cover and excess cement may cause dimples in the cover that will be visible after painting.
This project is ripe for "while you're there..." side jobs. The lower front valence was ready for replacement after losing a bout with a 5-gallon bucket of spackle that dropped off a truck. It's a good time to consider replacement or refurbishing of the signal lights and grilles.
Begin by jacking up the front and removing the grilles. This opens up access for the bolts and screws of the lower valence and the spoiler. Spray penetrating oil or WD-40 on the exposed threads of all the bolts and screws. Life will be easier if you can save and reuse the original fasteners.
Be alert for different screws in different locations. The factory used a number of different fasteners, and if any subsequent repair work was done, that greatly increases the likelihood of a mixture of screws. A hex-head sheetmetal screw is on the outboard end of the spoiler, while a machine screw occupies the hole right next to it.
The different screws you encounter can look pretty similar. With its tapered thread, the machine screw on the left looks a lot like the sheetmetal screw on the right. On older Corvettes, the fasteners you encounter are like a box of chocolates.
Take note of the different types of trapped washers on the bolts, too. The bolts with larger washers are used for the large holes in the lower valence, while the bolts with the smaller holes fit in the indented or recessed locations.
Removal of the lower valence and spoiler should be easy if the fasteners aren't rusty. You'll appreciate how much room you have to work here when it's time to reach inside to remove the bumper cover nuts.
If replacing or refinishing the lower front valence, pry the clips off now and bag them. It's easy to forget and throw the old panel away with the clips still attached.
Closely compare each replacement part with the original. Check the overall dimensions and shape and the size and location of every hole. It's much better to learn of any problems now instead of after repainting or during assembly.
Unbolting the side retainers takes a little patience. On the '73 convertible we are using for this article, the location of the upper nuts does not allow even a ratchet. It's wrench-only and one sixth of a turn at a time.
Place the upper retainer on the bumper cover to show where the studs are located. Manually raise and lock the headlamps for better access to the nuts holding the upper retainer.
Fortunately, the majority of the studs and nuts are visible from underneath if you look hard enough. The exception is the outer nut. A very short extension on a 1/4-inch ratchet or a 3/8-inch-long socket will get the job done.
Let's hope that you don't face a motley assortment of fasteners like these when removing the bumper cover. These definitely are not original. Where did the repairer even find four-sided nuts?
Many brackets, reinforcements, and braces become visible when the front bumper cover and bumper bar are removed. A steel reinforcement is pop-riveted to the fender on the lower inside edge, and another brace is pop riveted to the fender on its front edge.
Always Bag 'em Danno. Take the time to label and bag the fasteners. You'll be glad you did when it's time for reassembly.
It's not a pretty sight with the bumper cover removed. This is one job you'll want to finish as soon as possible. The large steel bumper bar is normally hidden behind the cover.
Drill the four 3/16-inch rivets that attach the lower retainer to the bumper cover. The lower retainer is sturdier than the upper retainer and often can be reused.
Test-fit the upper retainer to the upper panel. Clear or elongate any of the holes if necessary.
The upper retainer is not symmetrical; one corner is trimmed. Place the trimmed corner up when the retainer is installed into the bumper cover.
It takes some effort to work the upper retainer into the bumper cover. Start by inserting the center two studs and then work out to the ends on each side.
Test-fit the bumper cover after installing the retainers. Center the cover to the top panel and then make sure the bumper can be moved up or down as needed to make it flush with the top panel.
Check the fit on both sides at the fenders, too. There's only so much you can do at this stage, but at least be sure the holes are sufficiently elongated to achieve the best fit possible between the bumper cover and the body panels.
Elongate the holes if needed to enable the cover to be moved up, down, or to one side. A small rat-tail file or a Dremel tool are the best tools here. If the holes are significantly enlarged, small washers should be used under the nuts for the retainer.
A coat of POR 15 will keep the retainers from rusting, and provide a little help keeping the studs tight in the upper retainer. Two cautions: (1) make sure the POR 15 doesn't get on the threads-it's like cement, and (2) wear gloves or you'll be sporting POR 15 spots for days.
Install all the retainers to make sure they fit properly and to hold the urethane cover in its proper shape. Without the retainers, the bumper cover is too flexible for painting off the car. Mask all the exposed threads on the retainer studs.
If you're in Florida, California, or the Atlanta area, Carsmetics is an option for painting the bumper. They specialize in small repairs and apply DuPont paint that comes with a lifetime warranty (good at any DuPont AOQ shop). The cost was $350 for the bumper cover and lower valence (both painted off the car).
This shows how brittle the old cover had become-it broke in two when dropped in thick grass. The cover has one last service to perform. It will be used as a spray test panel by the painter to make sure the color match is acceptable.
While the bumper is being painted, it's a good time for the "while I'm there..." projects, like refinishing the screws and grilles in semi-gloss black.
With the bumper cover and bar removed, there was easy access for replacing the top panel support bracket and the energy-absorbing bolts. The large square die on the bolt is slightly smaller than the bolt shaft diameter. When the bumper bar is forced rearward during an impact, the die is pushed down the shaft stretching and extruding it to safely absorb some of the impact.
Rivet the bumper cover to the lower retainer with 3/16 aluminum rivets with large heads. This can be done before painting, or after to keep the rivet head natural. The rivet heads will be covered by the lower valance panel.
After the bumper cover is installed, the job is nearly done. It's a perfect time to replace a ragged spoiler. When trying to order a spoiler, it helps to know that it's also called an air dam or air deflector.
The last step is installation of the grille and lamp assemblies. The holes in the mounting brackets allow a little adjustment. If more is needed, elongate the holes. Bending the brackets risks cracking paint or fiberglass because they are riveted to the fenders.
New bumper cover install completed-sleek, shiny, looking fine and ready for at least another twenty years. Nip/Tuck couldn't do a better looking nose job.
C3 Corvette Bumper Repair - Simple Urethane Bumper Cap Fixes - Corvette Fever Magazine
In this tech guie CORVETTE FEVER shows you how to repair a C3 Corvette rubber front bumper by fixing the factory urethane bumper cap on a 1976 Chevrolet Corvette - Corvette Fever Magazine
1976 L48 Chevrolet Corvette - Vette Magazine
Read all about Jim Rhea's fully restored and resurrected 1976 Chevy L-48 Corvette - Vette Magazine
1979 Chevrolet Corvette - Bond Building
A duo of father and son restored this 1979 Chevrolet Corvette that took them thirteen years. Check out this Vette doused in '03 Dodge Viper Red paint!
C3 Bumper Cover Install - Replace Your Corvette's Urethane Bumper Cover - Corvette Fever Magazine
In this tech article CORVETTE FEVER provides a step-by-step guide to C3 Corvette urethane bumper cover replacement to show you how to swap the rubber nose on your '73-'82 Corvette - Corvette Fever Magazine
Connect With Us
Get Latest News and Articles.
Newsletter Sign Up
recent how to articles
Everything You Need to Know About Suspension Bushings for Your Corvette
March 1957 Chevy Convertible Gets a Custom Firewall & Floor
How to Pick Up Big Power On a Junkyard 454 With a Simple Cam Swap
How to Install Mini-Tubs in First-Gen Camaro to Accommodate Wider Rubber
How to Install a Modern Sound System That Hides Behind a Classic Look
subscribe to the magazine
Subscribe and Save 74% off the Cover Price!