subhamoy@gmail.com wrote:
> Hello all,
>
> Now that summer is here and temperatures are rising above 90 (in this
> part of Maryland), I have been noticing a peculiar problem with my '92
> Honda Accord. Especially on a hot day (though I am not sure about this
> correlation) after the car's been driven around for a bit, the brake
> pedals tend to get soft. Rather, at high speeds braking slows the car
> down. . . but the application of a persistent pressure causes the pedal
> to keep getting depressed without noticeable braking action. Pumping
> the brake resumes braking, and then it goes soft again until one
> releases and depresses the brake once more. The brake appears to work
> better during the initial braking action, and then gets soft after it
> has been depressed for a little while. There is no squealing,
> clinking, or any kind of noise or vibration.
>
> After reading these (very helpful) forums, I concluded that this may be
> due to water/gas contamination in my brake line, or a leaky master
> cylinder. I had the brake fluid flushed yesterday, and the entire
> brake system was checked out. There was no apparent leaks anywhere. .
> .and the brake fluid levels have always been constant. Today, I still
> find the same soft brake pedal problem.
>
> It is hard to get advice from car mechanics on this, because the
> problem is moody and sometimes difficult to reproduce. The car starts
> out fine in the morning. What do you guys suggest I do to fix this
> problem?
>
> Sincerely,
>
> Subhamoy.
>
a common symptom of the internal seals wearing is that they develop
grooves in their side wall that fluid can leak around. they work in
hard braking because the pressure deforms the seal for a close fit, and
when pumped, for the same reason, but under gradual braking,
particularly when hot, the symptoms are exactly as you describe.

if your car is an accord, i believe you can get a set of seals. if it's
a civic, you have to get the complete cylinder. either way, need to
take the master cylinder off and do the repair. doesn't take long.