1. Home
  2. BMW Cars and SUVs
  3. 750iL, 1991, 188K miles, brake pressure question

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:

formatting link
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

Reply to
Jan Fure
Loading thread data ...

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.

Reply to
R. Mark Clayton

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

Reply to
Jan Fure

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.