1994 940 wagon, 180K, original brake master cylinder, calipers and brake lines.

Recently I realized that the brake pedal can be pushed almost all the way to the floor with enough effort - probably 40 lbs force with the engine running. Front and rear pads are wearing evenly. The braking system has plenty of stopping power, on a dry road ABS can be activated with a hard push on the pedal. In normal driving the pedal only has to be depressed 2-3 inches to engage the brakes and stop the car.

With engine off, the brake pedal feels hard after pushing a couple of inches. However with constant pressure on the pedal, starting the engine causes the pedal to sink several more inches and it gets close to the floor. Turning off the engine, the pedal stays down so the booster is functioning OK with no vacuum leaks.

I just power bled the system with a Motive bleeder - no change. The master cylinder fluid level does not seem to be decreasing over several months. After reading the FAQ, I suspect either the master cylinder or rubber brake lines. The rubber lines all look OK but I havent yet checked for expansion under high line pressures.

Can a master cylinder problem cause the symptoms even though there is no fluid loss ?

Thanks,

Mike

91 740, 93 940, 94 940