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Thread: WHen turning the wheel and pressing the brake pedal i get this stop in power steering

  1. #1
    Join Date
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    WHen turning the wheel and pressing the brake pedal i get this stop in power steering

    Hello guys.
    When driving the car and then turning and braking I get this stop in power steering.
    THen when I turn harder it brakes loose again
    Has anyone had this before?

  2. #2
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    Had a 1991 BMW 850

    Start

    I would start with changing the filter in the Pentosin reservoir. Mine was black instead of tan.

  3. #3
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    Check the engine revs when this happens - low RPM can stop the power steering working correctly.

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  4. #4
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    Loose accessory belt?

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  6. #6
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    Is it not this situation the pressure accumulator aka "bomb" should prevent. This behavior could indicate that the "bomb" does not have enough pressure accumulated. Also check the pressure switches on the pressure regulator, mine where both inoperative giving no indication of low pressure.

    BTW, the "bomb" is still listed as available in RealOem but trying to order one from BMW dealership i Scandinavia indicates that they are not available in Germany.

  7. #7
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    I guess I will start with the bomb

  8. #8
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    Maybe it be my case of stalling? Sometimes the car stalls when I brake and clutch out. Usually when it's not in the operating limits.
    I just thought, maybe it's P/S related.

  9. #9
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    '97 840CI

    Executive summary

    A general concept...
    The pump's output curve (not shown) tells us that we get either high pressure at low volume OR low pressure at high volume.

    Two independent faults that actually happened...
    1) The steering box failed to seal, allowing constant high volume flow, lowering the entire system pressure, causing even a perfect brake system to look bad.
    2) The brake system was not perfect. There was a blockage at the input to the brake assist servo, making the entire system look ineffective. Not defended by accumulator and not caught by diagnostic sensor, because they are upstream.


    Encore..
    The (single, 840, bypass protected) filter is on the low pressure side and will have no immediate effect on steering or brakes. 850 situation will differ slightly.

  10. #10
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    Quote Originally Posted by Fatandre View Post
    I guess I will start with the bomb
    You will want to test for a failed brake boom.
    What happens is with a failed brake accumulator the brake booster draws a lot of hydraulic fluid and drops the pressure from the power steering pump such that the power steering looses assistance.
    You can test for a bad accumulator, with the engine stopped, by observing a rise in hydraulic fluid in the reservoir each time the brake pedal is depressed, 20 pedal depressions should deplete the fluid stored in the accumulator.
    Therefore, if the brake accumulator has failed the hydraulic fluid level will not rise in the reservoir.
    Also, brake assist ceases (hard pedal) once the engine is shut off, so you can apply the brakes several times to get the brake pedal feel with assistance, then shut off the engine and with a failed accumulator the brake pedal will immediately become hard.
    Also, if the brake pedal is depressed quickly with the engine running you may observe a flash of the instrument cluster brake indicator signifying a momentary loss of hydraulic pressure
    Last edited by m6bigdog; 09-01-2018 at 03:54 PM.

  11. #11
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    Quote Originally Posted by Hyper View Post
    A general concept...
    The pump's output curve (not shown) tells us that we get either high pressure at low volume OR low pressure at high volume.

    Two independent faults that actually happened...
    1) The steering box failed to seal, allowing constant high volume flow, lowering the entire system pressure, causing even a perfect brake system to look bad.
    2) The brake system was not perfect. There was a blockage at the input to the brake assist servo, making the entire system look ineffective. Not defended by accumulator and not caught by diagnostic sensor, because they are upstream.


    Encore..
    The (single, 840, bypass protected) filter is on the low pressure side and will have no immediate effect on steering or brakes. 850 situation will differ slightly.
    Is this for Servotronic system? Or standard as well?
    I get "bremsleitung" on the info dash for about 2-3 minutes after startup. Should I read ASC+T codes for understanding what's wrong? Or ABS? Or it's only try and replace?

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