I cannot imagine what the clunk could be in relation to the MC...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Evidently, it's the sound of the master cylinder "kicking the bucket."

Apparently reading comprehension isn't so strong with you, don't froget the qualifying "may" in there. Ntuarally, it could be a host other things, but the leaking at/around the grommet and mushy brakes are good indications that the prudent course of action on a 26yo car is to replace a cheap part to help ensure brakes are functioning at peak performance. Good luck with your reading comprehension goals in 2012.

BTW, when the master cylinder died on my old Chev Subruban back in 09, it sure made a nice bit of noise quite similar to a clunk...what are the odds?

I dont think you got the little joke there. No need to throw insults.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

x2.... the fellow is trying only to help you figure out the problem.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I had the same thing happen on my '85 which was fixed with a pair of reservoir gaskets, but since your's got soft, I'd suspect that there is air in a line, and with that much pedal movement, there's a possibility of master cylinder damage. Which leads to a more comprehensive brake system check.

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1985 300D-189k The 'UD', Ivory and Pinkamino
1979 300D-211k Dark Gray, Parchment
A 1980 Harley-~166k and
A 1994 Ford diesel pickup-349k and
A 1990 gasser Volvo wagon-145k

A spongy brake pedal is a symptom of air in the brake lines. Air in the brake lines is a natural consequence of an empty reservoir. An empty reservoir in the natural consequence of a leak. None of which is necessarily an indictment of the master cylinder itself. I would hate to see the OP replace his master cylinder (age unknown) only to find that he has a leaking caliper seal or brake hose.

The prudent course of action is to positively identify the source of the leak.