The test is two parts: Both the slow downward pedal movement under light pressure and the firmer pedal when pressing hard on it.

The slow pedal-to-the-floor happens because the piston seals are worn and fluid can slip past. With hard pressure the seals get pushed out onto the cylinder walls so they seal better.

Actually test #1 can be considered proof of a bad MC. The hard pressure part tells you that although the MC is failing, the car is somewhat driveable.

A few tips I've picked up on changing non-ABS 240 MC's.

It can be done without having to bleed the system. The idea is to have the two pressure lines disconnected for a very short time. That way any air that gets in will stay in the vertical lines, where it can float up into the reservoir and out.

Use a helper. Loosen up the mounting bolts to finger-tight. Loosen the two line fittings, but keep fluid from leaking. (Have a wipe-off rag at the ready, brake fluid eats paint.) Take off the mounting bolts. Take off the line fittings and pull out the MC. Hand old MC to helper and quickly put the new MC into place. Helper holds it there while you hook up the pressure lines. Tighten to finger-tight to be certain to not cross-thread the soft brass threads. As you can see, many variations are possible as to who does what.

Lastly - put in the mounting bolts and tighten, tighten the pressure fittings, and top up the reservoir to the full line. DOT-4, of course.

Take a slow test drive. Ideally the repair is done late in the day so the car can sit overnight and any air bubbles can float up and out before and serious driving is necessary.

Good Luck,

Bob

:>)