1968 Other Oldsmobile Models brakes remaining applied

Hey Jack, thanks for responding. The car is a '68 Olds Delmont 88, power drum brakes. The pedal travel has always been long, almost to the floor, yet stopped reliably. The master cylinder began to fail, in that pumping was required to effect a stop, and while stopped, pedal would drop, and the car would creep forward. Replaced m/c. Thereafter, pedal travel would slowly decrease while driving, becoming high and hard. Brakes would remain applied to the point of increased throttle pressure required to move forward. I'm wondering if the brake hoses may have deteriorated to the point of restricting the brake springs ability to force the fluid out of the wheel cylinders to return to the master, thereby resulting in brakes remaining engaged. Any ideas?

Thanks Jack. Same would apply to four wheel drum brakes, I'm guessing. Possibly just the rear hose, although both front hoses should be replaced, as well. Just to preclude further problems. Hope they're still available!

Jack, thanks for replying. The hoses, two front and one rear, were available through special order. Replaced all three; problem unchanged. Any additional thoughts on troubleshooting would be appreciated. I'm fresh out of ideas.

Jack, I closely examined the rebuilt unit against the m/c I was replacing. The bore depth of the piston was identical, as was the bore diameter and the line fitting sizes. I did not make any adjustment to the pushrod, although it is adjustable. Is there any possibility that the booster unit itself is at fault, and do you have any ideas on how to troubleshoot possible booster failure? I 'm really puzzled, as I've replaced many master cylinders, and never seen this condition before. Thanks.

Jack, again, thanks for your timely reply. When cold and initiallly pressed, the pedal travel seems normal. With each application thereafter, the travel lessens, and the brake pedal becomes increasingly higher and harder. Ultimately, throttle pressure is required in order to overcome the brake drag. Is there a procedure to absolutely determine if the booster is malfunctioning? Or would my only recourse be to change it out, and go from there? I'd hate to go to the expense in terms of purchasing a rebuilt booster, and installing it myself, only to have the problem persist. Any troubleshooting tips you're aware of? Thanks again.