Mate have had this problem on Outback... If its not in master cylinder there will be a dummy proportioning valve in there which can be replaced with the real deal... solving your problem. I came across this prob because one tonner utes have single spinner and proportioning valves at rear. The other has it in the master cylinder, like mine. You'll still have brakes without it... just 50/50 split. Think its supposed to be more like 70/30 split. I like it in master cylinder because its not dependant on load. Sent from my GT-S7583T using Tapatalk