Recently had an issue with the back of the driver's seat popping off. After reseating it a few times I realized that the problem was the lumbar support strap was pushing hard enough on the back of the seat to pop it off. The seat back isn't attached to the seat by any mechanical means, other than at the bottom, so it's just a pressure fit.

This became a perfect opportunity to adjust lumbar support. The pics will tell most of the story. It basically is a matter of stringing some stainless steel wire across the support strap, tightening the wire to suit the amount of lumbar support you like, and securing it.

John
1987 XJ-S V12