Installed my Racing Brake 2 piece rotors over the weekend without a hitch. Today I installed a set of Porterfield pads that I used a few times last year in preparation for this weekend at Summit. Right side - no problem. Left side won't budge after everything is tightened down. Any ideas? Need them quick or I'll have to choose between new rotors + stock pads or Porterfield pads + old rotors.

 

If you can't resolve the issue in time, put the old rotors back on (if they're still within proper thickness) and use the Porterfield pads. Are they R4 pads?
Pad compound > two piece rotor for safe tracking.

 

What is binding?? Is the rotor hitting the caliper...or the spindle? Or are the pads binding to the rotor??

 

Pads are binding to rotor. Can't turn wheel after installing pads. Rotor turns freely with stock pads.

 

Did you retract the caliper piston?..Is it stuck?? If the rotors are the same thickness..( check) and the pads are the same ( worked before) then the caliper or the hat must be the variable.....

There are different sized rotor rings that fit on the 2 pc hat....if you have the wrong one on the left side it could bind. Also there are different hats. RB may have mixed up on the order??

so...check the ring thickness...hat offset, and rotor diameter......

 

Indeed. Check all thicknesses and diameters and compare to stock. I know that DBA 4000 and 5000 rotors run thicker than OEM, so perhaps RB rotors do also.
Are you reseating the pistons correctly as dannobre points out? Make sure to get that piston all the way back in.

 

Mystery solved!!!! After some (O.K. alot of) choice words, lots of measuring and taking apart and putting back together, I found the problem. It seems that there is supposed to be a couple of special washers on the caliper mounting bracket that were missing from the factory. I remember them being on the other side because they kept falling off the caliper. Since this was the first time these brackets were taken off, they just weren't put on at the factory. The new rotors are a little thicker and the washer made the difference. Went to Mazda dealer and they don't sell the washers separately - have to buy bracket for $200 to get washers. Went to local brake shop and bought some washers for $.04 and VOILA I'm in business. Thanks for all the suggestions though. Now if only it didn't rain this weekend at Summit everything would be good.