I've been wrestling with a rear "gritty" feeling upon aggressive track brake application. I've been inspecting the heck out of pads and rotor surfaces and coming up empty -- they look great (Carbotech XP8s).
Expanding my search, I found something that might explain what I felt. I've got the old V1 Goodwin BBK installed on the car. This was installed by the PO and all I've done is basic maintenance (pad changes, lubricate pins, fluid flushing, etc.).
Looking closely at the allen-head pan bolts that secure the friction ring, they have almost no clearance to the caliper bracket. A close up of the bolt head shows that it looks like it's been hit with a file (all the bolt heads look like this). Pics:
Here's a reference photo I found on FM's website showing how that bolt looks when new:
I'm going to do some more teardown tonight to inspect the brackets for matching interference marks. Theory could be that when sufficient brake torque is applied, the brackets might bend sufficiently to contact those bolt heads?
Anybody ever heard of this? Perhaps I'm missing a spacer that should be used with this BBK?