ok i got all the parts to put rear disc brakes on the challenger the caliper bracket needs welded on but before that happens i need to know wich way to take the slack out of the caliper has 2 stainless allen head pins the caliper can slid across on. Do i shove the piston up against the rotor or the back all the way up against the rotor and let piston come out and take slack out?

when I did a disc conversion on a 9 1/4 I put a piece of cereal box cardboard between the pads and the rotor. This allows a small space to install new pads in the future. I then used compressed air to clamp and basicly center everything... remember on a 8 3/4 there is a inner seal that will need to be removed before welding....

rotors are new caliper is new,but there is at least 1/4 inch gap /slack dont have a way of useing compressed air

the caliper with the pads loaded into it, should be centered over the rotor with equal gaps front and rear between the pad's surface and the rotor's surface, I would locate/shim the caliper to position in it's static mode, do not charge the caliper

so your saying to put the pins halfway through travel also then set to centered on rotor? ralph