My dad has a 1988 Plymouth Sundance and the brakes go to the floor.?

The brake booster could possibly be malfunctioning, but more likely you have or are getting air in the line. Bleed it some more and if it doesnt fix it, your calipers may have a leak or the back brake pistons, or possibly a leak in one of the lines somewhere. Definitely check around the brakes to see if its leaking around them