My Brake Pedal Feel is Kicking My Butt... - Page 6 - BMW M5 Forum and M6 Forums
E39 M5 and E52 Z8 Discussion 1998-2003 Advertiser's Forum

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post #51 of 155 Old 25th December 2018, 08:32 PM
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The main reason for doing a bench bleed for a MC is to pre lube it. A little air being in it does not really matter, it will either come out the top on the return or go down on the push.
Don't waste time trying to bleed it in the car, it is pointless.
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post #52 of 155 Old 1st January 2019, 11:08 PM Thread Starter
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Hey, I am back..... Great B-Day and New Years!!!!


Back to the issue at hand.


I received the front and rear wheel speed sensors (pulse generator sensor). I did the multi-meter test and got reading for each as opposed to no readings on the old sensors. They are now installed.



I did a gravity bleed at each caliper letting fluid drip for about twenty minutes each. Then I used INPA software to work the DSC valves, pumps, etc... without opening the bleed nipples. Then I hooked up the Motive Power Bleeder, and while running Rheingold (ISTA+) with the bleed nipple open and end of bleed hose submerged in brake fluid. I triggered the pre-charge pump and pump with a final five long brake pedal pumps. Did not see any bubbles in the bleed hose.


I then started the engine and pressed the brake pedal which felt a little better. With the engine still running, I could fast pump the pedal and get some shorter travel.


Tomorrow I will put the wheels back on and drive around. I will go to a deserted parking lot and exercise the ABS/DSC to see if that is now working as it should (rapid pulse the brakes) and not lock up the wheels. I believe someone here said to just drive the car and the brake feel should come back in time.



If anyone has comments, please feel free to put them forward.
Thanks!!!!



To be continued....
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post #53 of 155 Old 2nd January 2019, 07:51 PM Thread Starter
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I did a test drive this am. My first impression was that the pedal feel and pad bite was little better. Drove the the deserted parking lot and with DSC enabled, I did some hard braking and hard sharp turns that got the DSC light to go on and off a number of times. With tires squealing and the DSC light flashing, I assume that is working, maybe? Under hard braking and the tires complaining, I don't think the ABS was working. I did not feel the brake pulsing. Right now I will drive the car as is. I never drive with the DSC on as it has a low threshold and is annoying to me.


I will keep monitoring the pedal feel and report back if there is any change as I put more miles on. My guess is that the gravity bleed made some difference for me.


It seems that quite a number of M5 owners have had this issue at some point. Not sure if there are many possibilities to this and no one fix for all.


Thanks People for your many inputs. This is a great site!!!!!!!!
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post #54 of 155 Old 2nd January 2019, 08:26 PM
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And your pedal doesn't go to floor anymore I assume?
Strange the ABS isn't working. I would scan for codes out of curiosity. Also go try the ABS on a dirt road.
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post #55 of 155 Old 2nd January 2019, 08:33 PM
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Try setting up ista to activate the solenoids again and then use a hammer or alike and tap the hydraulic side of the ABS while the activations are going on. Might free up any stuck noids.
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post #56 of 155 Old 3rd January 2019, 12:40 AM Thread Starter
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xrviz & sailor24,


Thanks for the tips!!! I will do both tomorrow if all goes well time wise for me.


Yes, the brake pedal does not go so deep to the floor as before. I am glad to see/feel some improvement!!!


Happy New Year!!!!!!!!!!!!!!!!!!
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post #57 of 155 Old 5th January 2019, 06:20 PM Thread Starter
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Update...


I took the beast for a drive yesterday. Did not turn off DSC. Did some hard straight line braking and found a grassy area where I could slide the car around left and right. I was able to pull the car down from 60 mph quite quickly and while on the grass the DSC light flickered a lot. When on the grass, I could not get a good wheel spinning tail out slide going. I assume the DSC is working. Later I used ISTA to work all of the valves, pumps and vents. I could hear all the clicks, pump noises, etc... with each device activation, so again, I assume that is working too.


Thinking this issue through:


1. The MC fluid volume that is moved in relation to the pedal travel is a fixed amount.

2. The caliper piston(s) and pad(s) travel to contact the rotors is quite short.
3. As the pedal travels closer to the floor (which it still does), where does the fluid volume go?
4. Can there still be a large air bubble hiding somewhere that refuses to expel while bleeding the brake system?


My ongoing concern is even though I can bring the car to a quick stop, it is the amount of pedal travel I have. My Porsche 1996 993 and Ford 2003 F-250 does not have anywhere the pedal travel that the M5 has now and in the past did not have.


There must be something I am missing...


I will continue to drive the car and get some miles on it and do a code scan to see/fix anything that may show up.


Thanks Everyone!!!!
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post #58 of 155 Old 5th January 2019, 10:08 PM
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Can you activate the ABS while driving? Can you activate it more on say a grass surface?
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post #59 of 155 Old 6th January 2019, 04:30 PM
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post #60 of 155 Old 8th January 2019, 12:33 AM Thread Starter
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My brain cells have been working overtime and keeping me awake at night...


Since my brake pedal goes way down to the floor, it appears to me, that there must be air hiding somewhere in the system. I decided to approach the bleeding process from a different direction that I saw on the internet. I am tired of pushing good, expensive brake fluid through the system and toss it out. What I tried is to run a plastic tube from the bleed nipple up to the MC reservoir and by pumping the brake pedal, push the fluid, and hopefully any air to expel at the reservoir. I raised the front of the up in the air, ran tubes from both front caliper nipples to the reservoir. Had both nipples open some and pumped the pedal with a slow pedal return. I could observe the clear tube and watch till no air bubbles passed by. I must have pumped the pedal seventy five times. Then I raised the rear of the car and did the same separately (left and then right) until no bubbles were seen. I did see some very small bubbles pass by while doing the front calipers and some larger bubbles from the rear. At this point I thought I was near the fix on this. However, upon starting the engine and pressing the pedal, it again went way down.


Later today I remounted the wheels and drove to a secluded place where I could test the DSC and ABS on grass and gravel road. Under hard acceleration and sharp turns the DSC light would light up. Hard braking on the gravel road did engage the ABS where I could feel the pulses. I did notice under the hard braking, when the car was almost stopped, with my foot still hard on the pedal, the pedal would drop lower maybe an inch or so. I repeated this several times with the same pedal drop. Is that normal???


So, yes the pedal seems to go way too far down to the floor.


I wonder if someone could take some measurements of their range of brake pedal travel for me to compare mine to? I used a tape measure with large numbers. With the edge of the tape resting on the top edge of the pedal and the end of the tape at almost right angles to the inclined section of the floorboard behind the pedals. I could lean over to the left and see the measurement to the front surface where the foot touches the pedal. I got measurements with engine off, the point where I could feel the booster is, and under full on foot pressure. Then with the engine running where the pedal ends with full on foot pressure.


After I took the measurements, with the engine off, I was able to push the pedal to the floor (3-1/2"). I let it return and pushed again, this time I measured 4-1/2" (some pump up), and again to 4" (no pump up), one more time all the way down to 3-1/2". Not sure what that means. I will read over the Vehicle Brake Information that xrviz provided and see if something clicks for me.


There is no slop in any of the caliper mounts, the calipers (just rebuilt), braided lines, new pads, new master cylinder. If the booster was bad, it would just make applying pressure harder. With the engine running, I can depress the pedal quite easily. It is when I apply firm, constant pressure, the pedal goes way down.


I don't like losing sleep over this but it is driving me totally nuts!!!!


Long Post but thanks for the input!!!!!
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