08-21-2018, 06:25 AM | #1 |
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Hey guys quick question, hoping someone can test this for me. I did my brake fluid flush as I was due for the service and I think I am being hypersensitive to brake pedal feel. The brake pedal feels perfect and stops on a dime while driving, nice and firm. If I stop in my driveway and hold the pedal, lift off the pedal and re apply light pressure on the brake pedal it feels a lot lighter. The pedal drops about 1/2" -1" when I re apply it very lightly. If the car moves 1' forward before I reapply the brake pedal is nice and firm again. I have a feeling it's the drive-off assist I am feeling as the rear calipers are slightly engaged until the car moves a little. Can someone just check there's for me to see if yours does the same thing please. I have bled the brakes several times w the power bleeder to make sure there's is no air. Thanks in advance guys!
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08-21-2018, 11:47 AM | #2 |
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Not tried mine but sounds normal to me. You'll probably get the exact same feeling if you press the pedal with handbrake applied then release the handbrake while keeping your foot on the brake. As the pistons in the rear calipers return, the fluid is pushed back into the master cylinder therefore pushing your pedal up.
Your thought of the brake holding the car sounds right to me. Sometimes the hydraulics will be held at the pressure the user last requested until the driver touches the throttle. Could be different on the M5 though. Last edited by Dwaynos; 08-21-2018 at 12:20 PM.. |
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08-22-2018, 05:10 PM | #3 | |
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08-23-2018, 10:23 AM | #4 | |
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Mine are due a fluid change. They feel soft, especially at the top of the pedal stroke, braking hard.. I’ll also replace the rubber hoses for braided for maximum improvement. |
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08-23-2018, 10:33 AM | #5 | ||
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08-23-2018, 03:31 PM | #6 |
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It's not a vacuum issue, as you said, the system will still be very effective at idle, the pedal will actually get harder if you pump it rapidly as it purges the servo.
Checked mine for you, as I mentioned in a previous post, I'm sure the auto hold maintaines the previous pressure and therefore holds the car still, if you touch the pedal again afterwards you have some free play before the pedal comes to a solid stop. If you move forwards or backwards then press the pedal again it feels normal. At that point the car had released the pressure and the pistons returned to their released positions. I'm not sure how much you are pressing the pedal when you say it feels a lot lighter, maybe you are referring to the extra free play in the pedal. Try pressing it further and see if it goes solid like I mentioned. Hope this helps. |
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08-23-2018, 03:41 PM | #7 | |
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08-23-2018, 04:13 PM | #8 |
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Yes that free play you experience is caused by the extra "space" inside the hydraulics when the pistons are held out.
Did you change to upgrade fluid or just a simple replacement? I need to do mine really but in two minds about changing to upgraded fluid. |
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08-23-2018, 04:15 PM | #9 |
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Thanks so much!!!! Yes, I flushed the brake fluid because it was due for service. I used factory BMW brake fluid. I used a motive power bleeder which made the job cake.
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08-23-2018, 04:39 PM | #11 |
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Auto hold I believe is on the newer cars, our cars it's called "Drive off assist." I holds the rear brake calipers closed for a few seconds during transition from brake pedal to accelerator.
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08-23-2018, 07:32 PM | #12 |
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There is no appreciable difference in pedal feel to me (very slightly spongy at the top and increasing firmness with increased pedal pressure) when braking with the drive off assistant engaged or after the drive off assistant has been engaged. At no time does my pedal go light. The only thing that creates a different pedal feel to me is pumping the brake pedal in which case the sponginess is gone from the top and it will be firm from the get go.
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08-23-2018, 07:37 PM | #13 | |
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08-23-2018, 07:48 PM | #14 |
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Mine actually has identical pedal feel when braking during driving as well. The identical very slight sponginess at the top is also present. My fluid is due to be replaced soon so I don't know if that will make a difference.
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08-23-2018, 07:56 PM | #15 |
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You may feel a nice difference when you change the fluid. Just make sure if you do it or have someone do it that they use a power bleeder. My local BMW charges 90 for brake fluid flush. GL and really, thank you for the reply!
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08-23-2018, 08:13 PM | #16 |
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Btw, the only time I believe my brake pedal is firm from the start while driving is under sudden braking. I believe we have a brake assist feature that increases brake pressure under sudden braking. Perhaps that is why you feel a firm pedal when braking while driving.
My car is still under a maintenance plan so my brake fluid will be done at the dealer. |
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08-23-2018, 08:17 PM | #17 | |
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09-10-2018, 11:27 AM | #18 |
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That's correct for the '13 and it may confuse a new owner on a hill waiting not knowing it will roll back after a few seconds after taking foot off the brake.
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