750iL, 1991, 188K miles, brake pressure question

Hi:

I have gotten some intermittent 'brake pressure' warnings, in the end I
was able to reproduce it by increasing the rpm to 2000 in park.

Following the diagnostics of sean750:

http://bmwe32.student.utwente.nl/sea...kePressure.htm

I tried disconnecting electrical connection to the top sensor, and the
warning went away. After the re-connection, I was unable to reproduce
the brake pressure warning. Could a poor electrical connection result
in intermittent warnings?

I see from the web link that Sean concluded that the top sensor was
faulty when the warning went away following disconnection of sensor.
How could he draw this conclusion? Does leaky sensor imply the sensor
is lying?

I did not experience weak power steering or extra effort required to
stop.

I opened the black cannister labelled 'CHF7.1' (hydraulic fluid?), and
found that the fluid level was at the bottom of the filter mesh (1 inch
below the lid).

I can see from the records that the previous owner had the following
brake or hydraulics parts changed during the last year:

1. Brake booster
2. P/S filter
3. P/S return hose
4. P/S pressure hose
5. P/S reservoir hose
6. Brake accumulator
7. Power steering pump

Are there any other parts that can result in wrong brake pressure?

The 2 brake pressure sensors appear to have a slight seepage of
hydraulic fluid, does that mean I should plan to replace the sensors
soon?

I am crossing my fingers and hoping this was just a corrected
electrical fault.

Jan Fure

"Jan Fure" > wrote in message
oups.com...
> Hi:
>
> I have gotten some intermittent 'brake pressure' warnings, in the end I
> was able to reproduce it by increasing the rpm to 2000 in park.
>
I notice the one thing you do not appear to have replaced is the brake fluid
itself.

If it gets wet (and it is hydroscopic) then brakes will fade due to the
water boiling on a hard stop / descent.

If you are a big strong person, then you should still be able to operate the
brakes manually without the hydraulic assistance. To check park the car on
a slight incline, engage neutral and release the handbrake with the engine
stop. You should still be able to steer and brake, although both will be
VERY heavy as the mechanical advantage without assistance is a lot less than
a [small] car that does not have it.

Hi Mark;

Thanks for the suggestion about changing the brake fluid, I have had
brake fade once with another car, and that was no fun, so I will indeed
change the brake fluid soon. As off today, I only have 1 year of
records, but the previous owner will give me records for the last 6
years, and my impression from conversation is that the pads and rotors
were changed 1 1/2 to 2 years ago.

Break fluid issue put aside, I have not actually ever noticed any hard
pedal, fading or weak braking power, or problems with the P/S assist.
The 'BRAKE PRESSURE' text accompagnied with an annoying warning ping
comes and goes, it was gone for a day after I cleaned the contact of
the top sensor, then it came back this morning. If the car is
stationary, I can cause the warning to go away by pumping the brake
pedal to exhaust the hydraulic pressure, at which time it may go away
for a few secods, and if it didn't come back before I start driving, it
will come back when engine RPM exceeds about 1500. Then after a while,
the warnings totally disappear, and do not come back until they choose
to.

I have decided I will change the pressure switches, the cost is only
$22/switch at my local European parts store.

Jan