One problem related to brake master cylinder has been reported for the 1998 Honda Civic. The most recently reported issues are listed below.
I completely lost by brakes on my 98 Honda Civic with no warning. I lost my front brakes and rear brakes at the same time and my foot completely went to the floor without any resistance. I down shifted and used my hand brake to get to the Honda dealer. The Honda dealer cleaned and repaired the brakes (they did not replace the brakes). The mechanic told me that my car only has one master cylinder. When one of the pistons in my rear brake popped out, I lost all 4 brakes.