Brake pad & disc alignment

the only car I know of that uses shims to adjust the caliper position is early Ferrari rear calipers. There is practically no clearance when the system is assembled, bled and used (on any disc system), the only reason (afaik) for the shims is to centre the caliper to the disc prior to bleeding and using.

You are aiming to centre the calliper (frame if claw type) slot on the disc with equal clearance on both sides. You doesn't need the pads or pistons. Only needs adjusting if, calliper, disc or hub is changed. For new pads just put it all back together as it was.

But it indicates really slack (read shoddy) tolerance in manufacture. Specs I have for Japanese car allows wear of 1mm per rotor face on ventilated disc and 1.5mm total on unventilated. The min pad thickness is always about 2mm so the body/frame can have a clearance slot 2mm wider than the disc and pad backing will still be fully in contact with frame/body with a fully worn disc.

That said in the last 3 years I've seen 2 pads without any brake material left at all lying on the road. Picked one up on a Jet engine makers car park in Derby. Get to see all sort of spare parts lying in gutter since I took up cycling for more than collecting car from MOT and welding.

Yeah, new calipers so unavoidable. So to what sort of accuracy is this centering required would you say? Are we talking thousandths here?

in the absence of any mfr. specs. I would be happy with an inequality up to one mm. It will make b.all difference in the real world.