Driver/Pass seat foundation bolts G/T M/H
A few months back I temp jacked up the driver seat because of leaning. It stopped the lean and the looseness also.
The looseness came back a few months later, so I decided to check.
Looking at picture 2 you can see the two canter bolts have been removed and the two outside bolts are loosened. There is a 1/6"-1/8" depression in all four mounting holes where the washer has dug into the foundation. Here's where the problem is as I reported earlier the floor is constructed of soft 5/8" glued flake-board followed by inches of Styrofoam insulation. The bottom sheath is 1/8" luan (like thin paneling) and topped with a thin layer of Fiberglas. Thats why the bolts continue to loosen and will for the future.
To fix it on the inboard side at the top I added a 3/16" measured shim under the seat foundation, this leveled the chair. Outside I fabricated 1/4" shim in a similar shape to spread the load of the bolts and washers. To aid the effort I used a 1/2" x 2" washer followed by the original 1/2" x 1 3/16 washer then a lock washer and a standard nut. The original was a nylok or self locking nut. Difficult to use be the bolt is a 1/2" carriage bolt in a drilled hole. Does not work very well.
The idea is to spread the bolt head load out on that thin luan surface, there is noting behind it for a couple of inches above or around it.
When I get the outside bolts changes I apply an asphalt paint to prevent rusting and water leakage.