Changing Brake fluid Affects Master Cylinder?

[Rich]

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

 

[Steve Bigelow]

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

Nope, but a bleed done to full stroke certainly will.

 

[Rich]

Nope, but a bleed done to full stroke certainly will.

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

 

[jim beam]

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

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.

 

[Rich]

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.

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

 

[Michael Pardee]

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

http://tegger.com/hondafaq/mastercylinderreplace/index.html