Overrun Clutch Piston

Make sure that check balls are not fixed.
Apply compressed air to check ball oil hole opposite the return spring. Make sure there is no air leakage.

Fig 1: Applying Compressed Air To Oil Hole (Overrun Clutch Piston)
Courtesy of NISSAN MOTOR CO., U.S.A.
Apply compressed air to oil hole on return spring side. Make sure that air leaks past ball.