The idler (intermediate) gear in the drive gears between the engine and transmission must have the end float set during any reassembly. The helical cut of these gears is designed to keep the noise down but also results in a side thrust that if not controlled will destroy the gearbox and flywheel housings. The end float of this gear is set by changing thrust washers with those of various sizes. The total end float should be keep between .003" to .006"
Shim for 1979-on idler gear with .875" pin diameter.