[s-cars] Brake light stays on.

[Fred Munro]

And clogged screens in the banjo bolts - missed a few on my original post.

Fred

-----Original Message-----
From: Kirby Smith [mailto:kirbyasmith at gwi.net]
Sent: January 22, 2005 10:17 PM
To: Fred Munro
Cc: Jack Gagnon; S-Car-List
Subject: Re: [s-cars] Brake light stays on.


Another item is a clogged filter screen in the hydraulic fluid reservoir.

kirby

Fred Munro wrote:
> Hi Jack;
>
> The light is telling you the hydraulic system pressure is low, as
validated
> by the loss of brake boost after two applications.
>
> This means that:
> 1) the bomb is toast and is not storing pressure or/and
> 2) system pressure is low and cannot charge the bomb.
>
> Item 1) is usually caused by loss of the nitrogen pad over time until
there
> is nothing left to compress in the bomb. This results in loss of boost
after
> a few (or one) brake applications. When the stored pressure is gone, you
can
> feel the pump pressure pulses in the pedal.
>
> Item 2) can be caused by:
> a) failed brake servo bypassing pressure from the bomb to the reservoir
> (tested by removing the servo RETURN line with the system pressurized. The
> servo should only be leaking a few drops per minute)
> b) pump air-locked or defective. Hard to test without proper pressure
> measuring equipment. Cracking the high pressure line doesn't tell you
much.
> I don't recommend doing this - it is dangerous to release high pressure
oil,
> makes a mess, and usually cuts the o-rings when the oil sprays out.
> c) stuck pressure relief valve in bomb (I'm assuming there is one there -
> I've never looked at the valving in one of these).
>
> I'd suggest flushing the Pentosin to see if that clears up the problem. It
> fixed my 30 second light problem for 2 years and is a cheap fix if it
works.
> Try the servo test to rule the servo out. You can't do the "bomb test" if
> you can't pressurize it.
>
> If the servo checks out OK it leaves the pump and the bomb as potential
> problems. You can feel the pressure pulses from the pump so it is putting
> something out. Given the age of your car, it would most likely be the
bomb -
> that's where I'd start as it is a more likely cause and is cheaper than
the
> pump. Better to replace the bomb and find you need a pump than replace the
> pump and find you need a bomb.
>
> HTH
>
> Fred Munro
> '94 S4
>
> -----Original Message-----
> From: s-car-list-bounces at audifans.com
> [mailto:s-car-list-bounces at audifans.com]On Behalf Of Jack Gagnon
> Sent: January 16, 2005 11:01 PM
> To: S-Car-List
> Subject: [s-cars] Brake light stays on.
>
>
> Hello,
>
> I am having trouble with my 92 S4.  The brake light does not go off no
mater
> how long I run the car.  It used to stay on for 10-30 seconds in the
morning
> and then stay off for the rest of the day.  It behaved like this for about
> two-three years of use.
>
> Just yesterday, it decided to stay on for good and I don't have power
brakes
> after the first or second application of the brakes.  I suspect the
> hydraulic pump, but the steering feels fine and I cracked the high
pressure
> line and the fluid squirts out just fine.
>
> Could it be a stuck valve pressure relief valve in the bomb?  Is it the
> servo in the master cylinder? or is it the pump.  I can feel the brake
pedal
> pulsate a little when the assist is used up.
>
>
> I have a bad feeling that this on could cost me a lot of money if it is
not
> diagnosed properly.
>
> Any help is appreciated.
>
> Thanks
>
> Jack