Completion of Rear Clip Repairs
In the last progress update the new rear valence panel and splash shields were fitted and bonded in their final positions. With that effort complete this update will focus on finalizing the repairs to the rear clip including filling the body seams, cutting openings in the tail lamp panel for the tail lights, and replacing the damaged rear deck vent drain tubes.
First on the to-do list was to fill in the body seams – the gaps between adjacent body panels. As many Corvette enthusiasts know, there are several ways to approach this task. At the factory the seams were simply filled with bonding compound and sanded smooth. Although this method works, and is used by many restorers, the joints sometimes crack due to flexing of the body panels or differential shrinkage in the panels or bonding compound. At the other end of the spectrum, some restorers will dish-out the seam by sanding down the panels along the seam, and then filling this area with fiberglass resin and matt to create a rigid, structural repair. While this is certainly the Cadillac approach, it’s a lot of additional effort.
For my project, I decided a solution somewhere in the middle made sense. After doing quite a bit of research, and talking to several other’s who have been through this process before, I decided to fill the seams with a structural epoxy adhesive. The primary benefit to using an epoxy filler\adhesive is that these products bond more tenaciously than ordinary bonding compound and are generally more durable, thereby reducing the likelihood of problems down the road
Ultimately I decided on 3M’s Automix 5885 “Plastic Repair Adhesive” for a variety of reasons. First, and most importantly, it is compatible with both fiberglass and polyester based body fillers and paints. Additionally, it’s sandable, has a decent working time (10 minutes), has a non-sag consistency when dispensed, and is a structural repair adhesive suitable for use as a filler. These are all critical selection criteria and this was one of the very few products I looked at that met all of the above criteria.
Because this is a two-part epoxy system you need a special dispensing gun to use the cartridges. Fortunately, I was able to get the Automix cartridges to work with the Lord Fusor dispenser gun I already had with a few minor tweaks (primarily adding a few shims at the top of the tube).
To fill the seams I simply followed the directions provided on the technical data sheet for the 3M product. The process was pretty simple and included cleaning and ‘dishing out’ the area to be filled, roughening the bonding surfaces with 80 grit sandpaper, working the material into the repair area, leveling out the repair with a putty knife, and finally sanding the cured epoxy smooth.
To start, the areas around the body seams were cleaned with lacquer thinner. Following this cleaning a die grinder equipped with an 80 grit sanding wheel was used to ‘dish out’ the seams and knock down any sharp edges.
Once the sanding work was finished the areas were cleaned once more with lacquer thinner. Next, a thin bead of adhesive was applied along the length of the seam…
…and the material was worked into the bonding surfaces using a putty knife. The purpose of this step was to ensure that all surfaces to receive the adhesive were fully wetted. Following this step the remainder of the seam was filled with adhesive. A putty knife was used to develop a fairly uniform surface just a bit higher than the surrounding fiberglass panels.
After being left to cure overnight the high spots were knocked down using a die grinder with a fine grit sanding disc. The important thing here is to keep the die grinder on a very low setting – just enough pressure to spin the disc. It’s easy to get carried away when sanding with a die grinder so an abundance of caution is warranted. Getting carried away can cause a lot of work later down the road. I was actually pleasantly surprised how easily and smoothly this material sanded, it was about the same amount of effort and finish as typical body filler.
Once the high spots were knocked down a sanding block was used to finish out the repair material. A crisscross pattern was used to help develop an even, uniform surface.
After finishing work with the epoxy adhesive, a skimcoat of body filler was applied over the general repair area and sanded smooth. My end goal in this process was not to develop a final surface, rather it was to develop a roughed-in surface a body shop could work with. Given that sanding body filler is not my favorite task, I plan to have the body shop finish out the final body lines and surfaces.
This same process was applied to all panel seams on the rear clip. After quite a bit of effort I’m glad to say my work here is nearly done!
The next task was to cut out the openings for the tail lamps and side marker lights. My replacement body panels didn’t come with these openings pre-cut, so I had to complete this task myself. Luckily, the process was fairly quick and painless. As shown in the photo below, there are several recessed areas that direct you to which areas need to be removed. And besides, if you’re off by an 1/8″ or so nobody will ever see it!
Despite the less-than-critical nature of this work I still suggest verifying the locations of the recessed areas before cutting just to be sure. I found some of the locations on my replacement panels were off by a hair.
Cutting the openings was pretty simple. The initial cuts were completed using a Dremel tool equipped with a Multipurpose Cutting Bit (Part #561). This made quick work of the cutting and, once the openings were roughed in, the large radius areas were finished smooth with an 80 grit flapwheel and the tighter radius areas were finished smooth using a smaller diameter sanding drum.
Next, the holes for the mounting studs were drilled out…
…and the edges of all cuts and drill holes were sanded with a 100 grit sanding block to smooth out the edges and remove any stray fibers.
The next, and final step to completing work on the rear clip, was to replace the rear deck vent drain tubes for the rear plenum (the tub located beneath the rear deck grilles). These drain tubes, which run from the rear plenum, through the passenger compartment, and empty into the rear wheel well, were accidently torn when I removed the rear deck. Thankfully, replacement tubes can be purchased for a fairly reasonable cost from most Corvette parts houses.
With the replacement drain tubes in hand the rivets holding the drain shields in place were drilled out, the old drain tube and drain shields were removed, and the mounting surfaces were thoroughly cleaned with lacquer thinner.
Here’s a before photo showing the old drain tube and drain shield as they came of the car…
…and here are the replacement tubes and clamps, along with the cleaned and painted vent caps, cleaned and ready for installation.
To ensure a watertight seal a good bead of exterior grade polyurethane sealant was applied to the mounting surface of the drain tube. My advice is to apply the sealant to the tube flange, and not to the surface of the wheel well. Otherwise, when you thread the drain tube through the hole in the wheel well, you’ll get sealant all over the tube which will quickly lead to a big mess (yes, I learned this lesson the hard way).
Once the sealant was applied the drain tube was put in place the holes in the vent tube, vent shield and wheel well were aligned, and new pop rivets were installed to secure the assembly in place.
So, after ten months and nearly 100 hours of labor, I can finally say the rear clip repairs are complete! It’s certainly felt like a lot longer, and a lot more effort, but it’s great to be able to walk out in the garage, see the end result, and know that the repairs have been done the right way!
In addition to the repairs documented in these updates I’ve also taken the time to test fit all of the tail lamps, side marker lights, as well as the rear bumpers, brackets and associated hardware. Now is definitely the time to fit everything since tweaks are often required to get things to fit properly. It’s really not something you’ll want to tackle after you’ve finished painting! For what it’s worth, and in hindsight, I probably should have fitted the rear bumpers DURING the installation of the various replacement body panels – the tail lamp panel in paticular. It would have made things align a bit easier. But, despite this oversight, things ended up fitting together fairly well – perhaps I just got lucky…
In any case, I’m glad to report that my next update will have absolutely nothing to do with repairing the rear clip. Instead, I’ll be focusing on getting the firewall reinstalled followed by the installation of a replacement one-piece front clip. I’ve learned a lot while fitting the replacement front clip so be sure to check back over the next few months to hear of my lessons learned.
And, with that said, I’ll conclude this update by wishing everyone a Happy Thanksgiving and a safe and healthy holiday season. While you wait on the next update why not drop by the Corvette Restoration Forum to share your project with others, or to participate in the upcoming holiday ‘pay-to-forward’ thread (look for it starting shortly after Thanksgiving). Lastly, if you haven’t done so already, please Like this project on Facebook to receive the latest news regarding project developments, updates and progress!