Undercarriage Tear Down
I won't go into too much detail here. It's much easier and cleaner than the engine bay. Using lacquer thinner, stripper, heat and tools I removed the old paint, dirt, grease, and undercoating, drilled out the soft aluminum body rivets, and removed the brackets. At the bumper cover flange corner is a bracket secured with panel adhesive. The location and bracket are shown. There was separation of adhesive at the flange.
Tear down included removing the fiberglass splash guards to allow full access to the #4 and #8 body mounts, which were badly damaged. Removing the splash guard can be tricky due to the contour at the lower portion, and care is required to prevent damaging the panel. I used a thin, flexible putty knife.
After tear down and inspection, I found many small fatigue cracks. Also, moderate rust in the #3 and #7 body mount chambers had caused separation of the seam sealant. There were three areas requiring major attention: the rear body mounts, bumper cover flange, and the union between the fiberglass and metal floor pans. To keep this a manageable length, these are linked below as separate, sub-projects.
Also, as shown in the series to the right, there were some cracks under the cargo ledge that I had to repair. Initially I thought I would grind out the old broken material and repair it with mat. However, the mat would not stay in the crevice. I ended up making a structural putty from nearly equal parts colloidal silica and 1/32" milled fiberglass. I added these components until the mixture was like cake frosting. I used a craft stick to pack the putty into the crevice and a grinding stone to shape it after it set up. As a final measure, I reinforced the repair with some fiberglass mat laid over the repair. The mat is green because I ran out of West Epoxy during the repairs and could not source any locally. There were still some repairs left and I needed to get the epoxy primer on in a couple days. I found a shop that sells All Resin by U.S. Chemical. It is a polyester based resin that is approved for SMC. While there are some things I like about it, it is a pain to work with so I will be refilling my West supplies.
There were some other minor cracks I repaired that I won't go into here, as the method is the same: grind, bevel, fill, shape, and sand. With the fiberglass work completed, it was time to spray the epoxy. I don't plan on showing pictures of the painted undercarriage
After the primer dried, I masked off the wheel well area and sprayed the undercarriage the same machine grey I used for the firewall. It turned our pretty poorly because I am a noob at painting. I learn each time, and this time I learned the effect that nozzle size and incident angle have on paint performance. I put rubberized undercoating in the wheel well and splash guard.
With the undercarriage painted, I could start putting the brackets back on. I began with the body mounts. First was the nut plate. This is a two-man job: one to hold the buck bar while the other flattens the rivet. I used an air hammer with a bit I cut flat. I set the pressure to 20 psi and used a 1 lb ball peen hammer for the buck bar. Use the air hammer on the rivet head. Overall I was pleased with the results.
In the second picture, you can see the grey paint, primer, and undercoating I used before putting the brackets on. The rivet head filled the depression nicely and was slightly indented relative to the mount surface.
Since I had to cover the original holes, I used the bracket to locate new ones. Once they were drilled, I was able to install the bracket using the same procedure. You can also clearly see the areas I had to build up so the bracket tabs would contact the body. Once those brackets were on, I attached the battery case and jack case brackets.
With major repairs complete and paint on the underside, I could start on the #3 and #7 body mount enclosure. I stripped the remaining paint and sealant out of the cavity. Originally the expanding foam was used and it had pulled away from the metal. After cleaning everything up, here's what I had.
Next I etched the surface with a 10% mixture of prep and etch and painted it with zero-rust. In this picture, you can see the gap between the fiberglass panel and the frame. This is filled by a preformed rubber block.
After the paint set up, I tried using brushable seam sealer to replace what I had taken out. I should have used the expanding foam sealer. The brushable sealant was too thick and didn't flow well into the gap. Once it dried there was no way I could see to get it out.
To fix the mistake as best I could, I bought some glue syringes like the kind used by jewelers. I sanded the steel bore to a 45 degree angle and filled the syringe with silicone. I was able to fill in most of the gap between the sealant and the body seam this way.
Now it was time to reattach the splash guards. I mixed a large batch of Evercoat SMC panel adhesive and working quickly, set the panels in place. Adhesive goes on the long outer edge of the panel where it touches the fender, across the top, and on the bonding area that touches the body pillar. There are some forms on the panel that help guide application. I used some spring clamps to hold them overnight while the adhesive set. Unfortunately, I cannot locate my pictures.
With the panels attached, this project is complete.
SUMMARY: This project was much more extensive than I anticipated. I knew repairing the mounts would be a task, but I had no idea the extent of what was involved or how tedious it was. The interior location of the motor mounts makes it very difficult to work in. Additionally, I was surprised at the damage to the rear deck supports, which I suppose is a result of over loading. This project took nearly a complete summer to accomplish. I'd give it an 8 - 10 just for the sheer volume of work required.
This was supposed to take a single summer, but it is the second summer and I'm still working on it. Documenting this in a sequential fashion is difficult because there is no clearly defined path to completion. Damage, corrosion, and other findings resulted in "side projects" not worthy of a dedicated page. These are covered here, resulting in a long walk through containing small, non-sequential tasks converging towards a finished rear undercarriage. If you do this, you will likely have side projects not covered here. As with other projects on this car, there were some things to think about.
FIBERGLASS PROTECTION: Like with the Engine Bay & Firewall project, I will use epoxy primer to seal and protect the exposed fiberglass. You can read more about that by selecting the hyperlink to that project included here.
WIRING: As with all old cars, terminals are corroded, wire insulation cracked, and plugs are brittle. I will rewire the car as a separate system walk through, but some prep work for that may be required here.
PAINT: I will paint the undercarriage to match the engine bay and powder coating the brackets and hooks. It's totally not necessary, and no one will likely see it, but it's good practice for me.