If the pedal goes down deep near the floor, then it is a hydraulic leak for sure or low fluid level. Might be in the master cylinder (new or not) or could be anywhere else in the system (lines, wheel cylinders, or front calipers).
Don't drive it like that. Find the problem and fix it.
Rev
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'66 Coupe, 306, 350-375 HP, C-4, 13.07 e.t., 104.8 mph, 1/4 mi.
O.B.C. #2
'66 coupe
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