When I have seen this problem it was a restriction in the brake hose. I whould replace the brake hoses if they are original. Use a synthetic brake caliper grease. Permatex makes a good one. Get a Mighty Vac vacuum pump for bleeding the brakes. This is a very usefull tool and I have gotten my monies worth with mine. It makes it very easy to bleed the new caliper and you can usually doing it alone on front brakes. If you can’t that indicates you may have a restriction in the brake line, like rust build up or a hose that has a restriction in it(as suggested above). If this happens get a helper to step on the pedal to help you bleed them. You should flush out the old fluid in the front lines and master cylinder. If you feel ambitious do the rear as well. You have an older car and there may be some rust in the lines.