Re: alfa-digest V7 #438 sinking brake pedal...

["Peter L. Krause" <pkrause@xxxxxxx>]

Mr. Davis,
    Your Spider's brake master cylinder is in the process of failing.
The sinking pedal without fluid loss indicates that the check valve
which prevents fluid return to the reservoir when the pedal is depressed
is sticking in the open position. This is likely due to the
deterioration of the rubber seals around the check valve, the detritus
allowing the valve to "hang" open. This problem is most apparent in cold
er weather and is better when the engine compartment heats up. If you
can sharply press the brake pedal and the pedal is high and hard, and if
you are at a stoplight and release the pedal slightly, then slowly
depress and it starts to sink, that is your problem. Be sure to replace
the master cylinder with the same bore size as is on your car currently,
either 20 or 22 mm. I prefer 22mm replacements for my customers cars
because the pedal feel is much better. Good Luck. -Peter Krause
PS Replacing the brake fluid will aggravate the problem by washing away
the goo that is creating a seal in the first place. No revisionist fluid
changes! just change fluid regularly after the master cylinder
replacement...

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