After noodling on the problem for a few weeks, I decided that the best place for me to mount the rear chassis to the rotisserie was the rear leaf spring shackle mounts. These are very rigid points in the chassis and there is no risk of crushing the rear frame rails with the fastener torque required to keep the mounts secured to the car.
Since I plan to finish the bottom of the car with spray bed liner material, I wanted to make sure that whatever mount I came up with would allow adequate access around the entire rotisserie mount so as not to act as a mask to the spraying process. I spent several days sketching up a design that would be strong, simple to make, and still offer maximum exposure of the entire frame areas that would need to be sand blasted and coated. What I ended up with was a solution that only required me to drill one hole in the rotisserie frame to lower the assembly by the 4¼” I needed to gain the working room I needed.
Satisfied I had something to work with; I turned four steel bushings that would fit the shackle mounts in the frame snugly. These were effectively a steel version of the shackle mount bushings for lack of a better description. From there, I fabricated two mount “towers” that would mount to the spring shackle bushings on the car and the rotisserie frame “arms” at the bottom. The 3” square tubing I used for the slip mounts allowed enough slack between the tower and frame arm that they would be self-aligning once the shackle mount was tightened.
Next, I focused my attention on getting the rotisserie frame cross pin hole relocated 4¼” up from the original location. This position would drop the frame assembly by that amount and allow me unencumbered access to the taillight panel and valence area. And after about 10 minutes with a handful of drill bits and my trusty hole-gun, the frame cross pin hole was relocated perfectly.
The final challenge was to decide how best to remove the rear of the car from the rotisserie frame so the new mount towers could be installed and the rotisserie frame relocated. Again, after careful measurement, I decided to make two wooded jack stand platforms that would allow me to secure the chassis in a free state while the conversion was made. With a little clever adjustment of the adjustable jacking posts I use to stabilize the car while doing the trunk work, I was able to get the car securely on the stands with no load on the rear rotisserie frame at all.
And about half an hour later, the rotisserie frame was lowered as required, the mounting towers were secured to the spring shackle mounts, and the car was comfortably back on the jacking posts, ready for the next phase of trunk floor and tail light panel repairs to continue.
|I made two pair of these steel bushings to fit into the rear spring shackle mounting location in the rear frame rail.|
|Here, you can get an idea of the "before-and-after" mounting styles. In the background is the saddle mount I used before and in the foreground, you can see the steel bushings for the new mounting location.|
|Here are the bushings with the grade 8 attachment hardware. Probably overkill, but I never worry with this level of fastener.|
|This shot gives you an idea what the mounting towers look like. These have yet to be drilled for the upper mounting holes, and the welds haven't been smoothed up, but they are otherwise complete.|
|A "side view" of the mount towers for detail.|
|I only had to drill one hole in the rotisserie frame to get everything positioned where I needed it.|
|Wooden step blocks were made to rest my jack stands on to secure the chassis while it was disconnected from the rotisserie and the new chassis mounts bolted into place.|
|With everything bolted back up, I mocked up the rear trunk floor enclosure to see that I had the room I needed to continue work.|
|Perfect! Plenty of working room for the valence as well.|
|This gives you an idea how much more room is available around the mount tower to allow me to spray primer, paint and bed liner coating on the entire rear frame rail without issue.|