That's exactly what happened on my truck. The master and slave cyl. for that car are about $60 each or you may be able to buy rebuild kits for them for probably less than $20. In my experience, the master cylinder craps out first.

To determine if that's the problem, have her press the pedal slowly and you watch the release fork at the same time. If you see very little motion out of it (1" or less), that's probably it. Of course, there may also be obvious signs of failure like leakage. Something else to consider is that the master cyl is just low on brake fluid and it's sucking air. If it is, you'll have to bleed it like brakes when it's re-filled.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250