Changing Brake fluid Affects Master Cylinder?

Four days ago I had my 1993 Accord serviced. Among other things, I had the brake fluid changed & the brakes inspected. The car has 149,000 miles on it, the front pads were replaced at 49,000 miles & the rear
shoes are original. Anyway, I picked the car up on Monday & drove about 12 miles home & everything was fine. Friday I get back in the car for the first time & the brake pedal sinks to the floor. I check the brake fluid & it is full. I limp back to the mechanic(who I trust) who tells me the master cylinder just happened to go bad. He said the old fluid is thicker than new & that may be all the old MC needed to go. He replaced the MC & deducted the cost of the fluid change he had just done($247 - $75= $172 for new MC installed). Anyone ever hear of new brake fluid pushing a 12 year old MC over the edge? Thanks, Rich
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Nope, but a bleed done to full stroke certainly will.
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Steve Bigelow wrote:

Is it that a bleed should not be done to full stroke or are you saying a normal brake bleed will cause an old MC to fail? Thanks, Rich
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Rich wrote:

personally, i don't put too much creedance in the "can't bleed full stroke" theory. i've bled master cylinders with pressure bleeders, /zero/ stroke, and still had seals disintegrate the next week. my opinion is that unless you change the fluid regularly, the fluid gets contaminated. this swells the rubbers. these swollen rubbers wear to fit the cylinder in the expanded state. when you change to fresh fluid, which contains rubber conditioners, the seals shrink slightly, and then they start leaking.
bottom line, if the cylinder's given you 150k, you're doing just fine. change it, do another 150k. it's peanuts. next time, make sure you flush the brake fluid annually - i'll bet you it lasts a good deal longer.
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jim beam wrote:

I tend to believe that is what happened. I thought that I had changed the fluid at least once before but upon checking of my records, it seems that I never did. It seems the only thing the mechanic might have done "wrong" was to not warn me of this possibility. Either way, a master cylinder replacement was imminent either now or the next time I had major brake work done which required bleeding. Thanks for your expert assessment. Rich
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http://tegger.com/hondafaq/mastercylinderreplace/index.html
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