(OT) Auto brakes question

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 puzzled.
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snipped-for-privacy@highway.com wrote:

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).
Erik
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snipped-for-privacy@highway.com wrote in news:c3mh58d1s695mf8nnipp39lurb1uami2ei@ 4ax.com:

Does the master cylinder cap have a fluid-level sensor? If so, it may be defective, or its wires may be losing contact intermittently.
--
Tegger

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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 indicated.
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There is always an easy solution to every human problem -- neat,
plausible, and wrong." (H L Mencken)
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On Sep 18, 7:31 pm, snipped-for-privacy@sdf.lNoOnSePsAtMar.org (Larry W) wrote:

if your not certain take it to a pro mechanic
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wrote:

+1
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