Re: Brake Idiot Light

[zm@mhcnet.att.com (Zafer Mehmood [209])]

> > I have an 91 V8.  My "brake" light comes on and stays on in the morning
> > for approximately 30-40 seconds when the car is first started.  This happens
> > only in the morning after the car has been sitting overnight.  If I stop the
> > car on the way to work, and restart it, it turns off right away.  After
> > parking it all day at my office and starting it in the afternoon, it turns
> > off right away.  Unlike Peter's case, stabbing the brakes doesn't extinguish
> > the light, nor does re-engaging and disengaging the parking brake.  The
> > light turns off only when it feels like it.  The brakes seem to work fine
> > even when the light is illuminated.  I've made cursory checks for fluid
> > leaks and haven't noticed any.  Any ideas?

Sounds very much like the problem I had in my '87 5000TQ. I don't know if
your '91 V8 uses a similar setup, so take it with a grain of salt...

In my case, the brake pressure accumulator was bad and was loosing pressure
overnight. This accumulator stores brake boost pressure for providing the
"power brake effect" for several pedal applications if the engine stalls
or is shut down. With a leaky pressure accumulator, the brake warning light
comes on upon intial startup to indicate a "low pressure" condition. During
this time, the brake pedal feels quite hard, i.e., no power effect. Once
the pump builds up the pressure again, the light turns off. You can try
revving the engine to say 2500 rpm after initial startup to see if the
brake light shuts off faster than the typical 30-40 seconds that you've
noticed. If so, this would reconfirm that the pump is able to rebuild
the pressure faster due to the higher revs. If the accumulator
is leaky enough, you should be able to create this low pressure condition
anytime the engine is idling by pumping the brake pedal several times, and
the brake light will come on. At least, on my car this is how it behaved.
Changed the pressure accumulator myself ($195 at PAP on sale vs. $326 at
dealer) and the problem is solved.

Zafer


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Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ