The brake pedal on my 77 F350 goes nearly to the floor during braking. All brake components, including the master cylinder, were replaced about 8 months ago. The vacuum booster was not replaced. All was good until about a week ago when I noticed the brake pedal needed more and more travel to get any braking action. There does'nt appear to be any leaks and the master cylinder is always full. The rear brakes seem to be adjusted as the truck does stop well and the parking brake works fine.

Any ideas?

Thanks, Randy

 

Master cylinder failing.

check booster push rod adjustment.

 

you said everything is new right? then double check the rear brake adjustment. if the adjusters are not working right they can unadjust. and you get more pedal travel.

 

Thank you both for the tips.