The earlier QM disc hubs were touching after a small amount of wear on the discs, causing them to "wear out" early. Someone figured out that if you machine the hubs slightly, the pucks are able to wear properly.
Quoting BrandonEchols:
Quoting 4thStroke:
I would go with the Quarter Master with the TMZ gear drive hub if you need a twin disc.
The clutches are very similar, but the TMZ discs with the gear grive hub is far superior.
In what way?
Instead of having two small hubs, there is one large hub with splines on that hub that the other disc slides onto. The hubs will never touch and the contact on the input shaft is maximized. The car was only making 440whp and 335tq. I use a twin because I do run ethanol from time to time and need a clutch to hold up. We all know these trannys are fragile, so I also wanted a clutch that was going to allow me to shift as clean as possible to help keep me from buzzin synchros and grinding gears. The twin can also kill a tranny very easy if you start side stepping and if you have the false sense of security that because you have a twin, your tranny will shift nicely.
It wasn't long before my hubs had more slop than I cared for, so I upgraded the discs to the TMZ discs. Drive ability is better and there is slightly less noise.