Hi Brian,
As its a fairly old car you may have a split in the vacuum hose to the brake servo.
The hose you are looking for is the one (often cloth covered rather than plain rubber but not always) that is plugged into the round metal thing just behind the brake fluid reservoir. That is your brake servo. Trace the hose and check for cracks or splits in it. If that hose is split and allowing air in then the "power assistance" goes from your brakes meaning you have to press quite hard for any effect.
You should be able to get a second hand hose from any scrapyard, but obviously check that one for any signs of perishing too.
Also check your brake fluid level is at max. If it is very low you will probably need to bleed your brakes, which takes 2 people realistically, unless you have the right gear.
Mark L., July 2004
