brake sinks only in hot weather

Just recently, my 1991 Honda Accord has had brake problems. Only when it is hot out and the car has been in the sun, the brake pedal goes down to the floor with no appareet brake pad contact. When it cools
down outside, things are fine. I just had the brake fluid changed. If it is a master cylinder or hose, why would it only happen when it is hot outside, even when I only drive it for a few miles.
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I can't think of a time when brake pedal sinking was anything besides the master cylinder (assuming there was no big leak somewhere.) I bet if you wrap the master cylinder in cold rags after it starts sinking the sinking will slow or stop. Or just take the short cut and replace the master cylinder. If it's the original, it's definitely lived a long life.
Mike
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snipped-for-privacy@aol.com wrote:

you can get seal-only kits from majestic honda or replace the whole cylinder.
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jim beam wrote:

thanks -- any idea what this will run in $$?
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snipped-for-privacy@aol.com wrote in wrote:

Most of the local auto parts stores are online,you can check parts availability and pricing easily.
--
Jim Yanik
jyanik
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On 26 Jul 2006 07:21:51 -0700, snipped-for-privacy@aol.com wrote:

I was losing brake fluid (91 Accord) and the problem was that the white plastic reservoir that sits on top of the Master Cylinder had a crack at the bottom. You can't get that part separately, it's only sold as part of the MC. So I went to the local junkyard and got a used MC for $40, took the cup off and replaced the cracked one. Works fine.
That, however, left me with an unneeded used MC which is currently sitting in a plastic bag on the floor of my garage. If you want it I'll be happy to drop it in the mail. Ill monitor a junk email account and if you want it just send your address to:
takethebird@(dropthis part out-even junk accounts deserve a break)hotmail.com
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I'm looking for this kit. My seals are shot. I've looked for it at Sleandro Honda and Majestic and found none under their listings. Where would it be?
Thanks
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Sam Nickaby wrote:

high volume stuff like 13/16" civics, etc. if majestic don't list it, you can't get it and whole cylinder is your only option.
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snipped-for-privacy@aol.com wrote:

Probably a master cylinder. The bore expands as the temperature rises, so it might be right on the edge. In any case, replace it!
John
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