Thats a symptom of a master cylinder push rod adjusted to far and its not letting the master cylinder plunger come back far enough....Fluid can only return to the master when it's all the way back.
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
