A limited slip differential transmission of the closed type in which a pressurized lubricant is fed to the rotating gears and a series of limited slip clutch plates. The clutch plates are engaged by pressurized control fluid. A valve assembly having a spool valve is responsive to engagement pressure to permit discharge of a portion of pressurized fluid from the clutch plates to a sump chamber and the transmission to purge debris that may have accumulated in the clutch plates. The spool valve is arranged so that fluid is passed only during an intermediate movement of the valve to minimize any pressure loss from the lubricating fluid for the transmission and limited slip clutches.