cool. you may have a silvia one on there. theres a part number stamped on the end of it. like 69f, or 05u etc etc the s15 one is the same a gtr one but sends double the pressure to the rear brakes. you need to peel back the alloy cap on the end of the master. just poke a screwdriver thru it. then theres an 8mm allen key. un do it and shorten the spring or use a gtr one. if not just keep shortening it till it doesnt lock up.
ive got the exact oposite problem. my alcons up front are to grippy compared to the ap,s on the rear lol.