After ~34 years of continual use, the shock mounts became weaker, until one day, the back of the chair fell away from the seat shell.
After much study, the following repair was born. This was a necessity because the mfr. could not guarantee a repair and said that if the seat shell would not repair, a substitute shell of a different angle and wood specie would have to be made. Brazilian rosewood is no longer available for harvest.
To disassemble the chair base and shell is not a difficult task.
1. Slide the seat cushion forward and lay aside.
2. Remove the armrests, two screws each, from the under-outside, using a #3 Philips head screw driver.
3. Remove the two inside screws from the steel "L" arm brackets holding the seat shell to the brackets. One or both of these may be loose if yours broke like mine. Lay the back aside.
4. You may elect to remove the aluminum base for ease of the repair. You should now have a seat shell w/ broken rubber mounts attached to the inside of the wooden shell "tabs."
5. The remaining broken rubber mounts will have to be carefully removed from the inside of the seat shell tabs.
6. Special Note: Save the embedded metal plates from inside the broken shock mounts. These will be reused when making the new shock mounts.
7. I used a SHARKSAW: pullsaw trim & detail double saw, no. 10-2205 to cut the remaining rubber from the seat shell. In order not to cut the precious rosewood, I taped some ~ 26 ga. metal strips adjacent to the work as a guide for the saw. This left about ~26 ga. thick rubber to be removed w/ blocked fine grit sandpaper. The closer to the rosewood I came, the finer the grit. Before the rubber was completely gone, I traced the outline of the tabs and the profile of the shock mount, so I could position the new mounts I was about to make.
8. Materials needed for the new shock mounts:
a. Two 9/32" thick maple blocks, shaped to fit the outline of the original shock mounts. Be sure the grain runs w/ the long dimension of the outline and that the annual rings are "parallel" to the broad side of the block.
b. Two 2/32" rubber sheet cut to fit the outline.
c. Two cleaned and roughened, salvaged steel plates.
d. Sixteen short FH machine screws, to drop into the salvaged plate holes and into the drilled maple block holes.
e. An excellent epoxy repair kit. I used WEST SYSTEM Inc.'s 101-6 Maxi REPAIR PACK, w/ the included bonding filler.
9. You will need to prepare the maple blocks, rubber sheets and salvaged plates by drilling the blocks to accept the fasteners, and by roughening all broad surfaces to aid the epoxy bonding.
10. Assemble the material "sandwiches" using the epoxy directions and diagram here.
11. After the epoxied sandwiches are cured, epoxy the sandwiches' maple faces to the inside of the prepared seat shell tabs.
12. I tried to clamp my work, but the materials kept sliding, so I ended up weighting them instead.
13. To disassemble and reassemble the chair back to the finished seat shell shock mounts, I laid the chair on it's sides. Plush carpeting helps here.
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2. My repair has lasted over 10 years w/ daily use. Good luck w/ your repair.