Re: More Brake Problems

[raf40@oes.amdahl.com (Richard Funnell)]

Al,

>But the damn brake light NOW stays on 'most all the time!!!  Oh, it
>might go out for a few minutes, but it's at random times as far as I
>can discern...there's no pattern.
>
>So - I *WAS* ready to be convinced the only problem was a faulty
>pressure warning light, because there was no other problem appearing.
>The switch screws into the brake servo and is easy to replace.
>
>But TODAY, my wife said the brakes felt spongy twice when she started
>it after it had been sitting for 3+ hours.
>

I'm not sure about your model, but on my urQ the warning light can come on
for three reasons.  These are low boost pressure (this is the sensor you
are referring to), low brake fluid and the parking brake not fully
disengaged.  I would check for these three conditions, and then
disconnect/defeat the sensors from each one.  Reconnecting each sensor in
turn should tell you why it thinks it has a problem.

As far as why it has a problem, that's more difficult.  Once the sensors
are checked, they may help.  If the PA was bad, I would expect the pedal to
feel fine once it was up to pressure.  I have replaced mine twice, and both
times the symptom was no boost if I hammered the pedal hard and fast.
Boost would reappear in a fraction of a second that seemed like a lifetime
if it wasn't a test.  The light would be on only while boost wasn't
present.

Counting the number of times the pedal can be pumped before it feels like
it hit a rock is a good test of the PA.  If it goes more than 20, it is
usually fine.  After that, you might try checking the power steering fluid,
and bleeding the brakes.

Good luck.

Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL