My 273 would start slipping in 4th gear in about a month. I switched over to a 340 10.5 system in the 70's. Then back again to 9 1/2 / 10 inch for the almost stock Formula S. Still slips too soon in 4th gear. I ordered one of the new single disc 9 1/2 pressure plate, disc, and flywheel from Brewers.
