The Green Book says that maximum radial throw allowed is 0.006" (0.15mm). The problem with grinding the drums is that new shoes won't match the radius. Volvo has very specific instructions about grinding the shoes to match the drums. Pre disc brakes that procedure was common but finding someone with facilities to do that now may be difficult. Not doing this may mean that the full surface of the lining may never contact the drum even after many thousands of miles. This is also one of the reasons that the PV brakes are notorious for pulling to one side or the other when braking. Quick hard breaking can have you off the road or or into the opposite lane. Not good!
Rob's rationale, shown I think in one of his videos, is that if you reduce the thickness of the drum, it greatly reduces its ability to dissipate heat. Being rally orientated this is very important but perhaps normal quiet motoring on normal roads would stress them too much.
Green Book -Brake Drum - Check the friction surfaces of the brake drums and radial throw. The radial throw shouldn't exceed 0.15mm (0.006"). If the surface is hollow, scratched or cracked the drum should be replaced. Rust spots or small scratches can, however, be polished or ground off."
|