I am installing dual master cylinder below the floor. There is lots written about needing a 2 psi residual valve for disc brakes and 10 psi for drums. My question is does the clutch master need a residual valve. The application is actually a car, but should be the same as our old trucks.

 

you would only need one if your if the master was lower then the slave cyl

 

I would think a res valve on a clutch would always keep alittle pressure on the throwout bearing, causing wear.

 

From what I`ve seen clutch master cylinders are higher than the slave.

 

It really doesn't matter what the relationship between the slave and master is for a clutch. As soon as the pressure plate isn't pushing back on the slave, there is nothing to cause fluid to go back into the master. Rusty has it right, you don't want the release bearing riding the PP when the clutch is released.