My brakes on my older Chevy seem to work fine, but several times lately
when I've had to brake fast, the brake light comes on. On normal
braking it does not come on. The master cylinder fluid is full, and
there are no leaks in the lines that can be seen. The car has a
proportioning valve, and I assume that valve is not getting even
pressure to cause the light to come on. The question is why? Could the
master cylinder be bad, yet still stop the car properly? This has me
Does it have a reservoir fluid level sensor?
If so, it may not be adjusted (or assembled correctly), and turning on
the light when the fluid sloshes forward during stops. Try doing a
simulated stop with the engine running, and car stopped. If you still
get the light, it's not the level sensor (if so equipped).
Could be proportioning valve but master cylinder is more likely. It can
leak internally or bypass fluid around one of the pistons causing a
pressure difference high enough to activate the warning light switch.
Depending on how bad it is, it could be unnoticeable, especially if only
the rear brakes are being affected. If you ever notice any pedal fade,
and are sure there are no external leaks, replacement of the MC is
There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)
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