what is blow by for brake master cylinder end up in a 1991 honda accord LX

I think that you may be referring to fluid by pass, this is when under light pedal pressure fluid passes past the primary master cylinder cup seal and you get a sinking pedal, poor breaking and no sign of fluid loss.

Yes,correct but where does the brake fluid go since there are no visible signs of a leak? Thanks mhpautos.

It just bypasses the seal and stays in the rear of the master which is still the resiviour. We are talking aboyt only a few ml of fluid here.

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