Corolla Brake Issue?

[Corollaman15]

I have a 1.8 vvtl i 2003 with a brake issue ,the rear wheels binding so far I have checked the calliper pistons and slide pins are free it points to a fluid issue off not returning properly because if I press the brackes the back brackes stay on but the slights nudge off the wheel/callipers it frees right away because of this I have changed the master cylinder and brake fleckies and also changed the brake fluid I an out of idears and don't know what to do next any help much appreciated

[TomdeGuerre]

It could be your brake proportioning valve sticking. Have a look at this post (although it's about pipes to the valve being crossed which is not your problem but it includes a pic of said valve).

http://www.toyotaownersclub.com/forums/topic/139491-proportioning-valve-crossed-the-lines-for-rear-wheels/

[Corollaman15]

Thanks mate seems to have an issue gave it a few taps test drive an no warm brakes need to find a valve now