My Brake Pedal Feel is Kicking My Butt... - Page 5 - BMW M5 Forum and M6 Forums
E39 M5 and E52 Z8 Discussion 1998-2003 Advertiser's Forum

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post #41 of 155 Old 22nd December 2018, 02:20 AM
josiahg52
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I'd forego the diode function and just obtain a resistance indication. I assume you have a digital multimeter probably with 1, 100 and 1000 ohm ranges perhaps? Or maybe an auto-range? Someone else can recommend the range but if something told you to use the diode test function then use the lowest range.

When taking resistancee measurements, besides a general inspection of the meter and leads that you should always perform prior to any use, short the leads together first to ensure they have continuity. If measuring voltage, always check voltage on a known live source in the range you are using on the meter before and after the check.

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post #42 of 155 Old 22nd December 2018, 02:58 AM Thread Starter
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salor24, josiahg52,



My multi-meter was set to the diode icon, there is no range setting, just min/max. If I touch the probes together, I get a very brief numbers flash before it goes to 0 or maybe 0L. I can try taking Ohm readings, what might they be? I have a suspicion that maybe the wheel speed sensor(s) because the ABS does not feel like it is working. Under very hard braking I can lock up the wheels and not feel the ABS pulses.


I wish there is a detailed (how to perform) step by step flow chart to fully test every thing to debug this out. I have found many 'how to' do not detail every tiny step that could make a difference. Don't assume anything by the person doing the tests.


Thanks again...
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post #43 of 155 Old 22nd December 2018, 03:36 AM
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What meter do you have exactly?

There is a difference between 0 and OL. 0 or zero would indicate a shorted diode. OL is overload and means you are reverse biasing the diode or it is open. Assuming how your meter operates, I'd expect an indication less than one volt and maybe an audible indication. That's even if this is the proper measurement to be obtaining for these sensors. I thought you measured voltage while spinning the wheel or somehow a magnet was involved. Fortunately, I've never had to do these tests.

Are you sure you are in the right mode? None of my meters have a direct diode check function. Buttons have to pressed after moving the selector switch. Personally, I never use the diode check function.

What is true is if while in the resistance mode, shorting the leads together does not result in continuity less than one ohm, the leads or meter are faulty.

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post #44 of 155 Old 22nd December 2018, 03:51 AM
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Your description might indicate that you have a solenoid not working. It might be electrically sound but stuck open or closed. If you had an electrical problem including a failed wheel sensor the computer would know and turn the unit off. If you had a wheel speed sensor out the tire control(flat tire monitor) would become inactive at minimum, but sure as anything the DSC and ABS would turn off and you would have lights galore.


To check a diode you set a meter to ohm's lowest is easiest although starting on the highest range and working down might be safer. The gist is on ohms connect one lead to one side the other to the other side and read. It will be a reading that is not 0 then switch the leads and do it again, the other way should be 0. Depending on your luck it could be the opposite. A diode will let electricity through one way only. Since your meter tests ohms by sending the electricity through the circuit from the meter battery, you will get a reading in one direction but if the diode is working it will block the electricity the other direction.
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post #45 of 155 Old 22nd December 2018, 04:08 AM
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To be clear, my last post is describing how I assume your meter should present a diode indication. Sailor24 is describing how to use the resistance function to check a diode which is what I was alluding to in my post before last and is what I recommend doing.

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post #46 of 155 Old 22nd December 2018, 05:33 PM
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You are correct to use the diode setting on your multimeter. If it has a maximum function even better, it will the show the max voltage over a period of time. Spin the wheel as fast as you can to get the readout.
But...... I believe this is all a waste of time. As said before, if you don't have trifecta lights, tire control inactive, and correspsonding fault codes, then your WSS ABS DSC system is working and you have a mechanical issue.
Be especially careful working at the DSC connector. Never put a testing wire or probe into the small square hole, you will ruin the female connector for the pins and have to replace.
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post #47 of 155 Old 22nd December 2018, 05:50 PM Thread Starter
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I just did a resistance test with audio on all four sensors at the female sensor connection. No reading or sound with the test probes reversed or not. I had the meter set to Ohms, the lowest setting. All four sensors seem to be dead.


I will have to deal with a bad male wheel sensor connector at the left front wheel. It was so brittle that it cracked into small pieces until I was able to pull what was left of the terminal body out. The female portion all seem to be fine. I might be able to reuse this and reseal it. I will apply a coating of non-conductive electrical grease when I install the new sensors.



I will now run Rheingold (ISTA+) BMW testing software to check for codes. Right now, all four wheel speed sensors and the large connector at the ABS/DSC unit are disconnected. Codes came up as expected:


S0018 No Communication with traction control system
000075 DME: Servotronic: no roadspeed signal
000084 DME: CAN timeout DSC
00008B DME: Interruption, Tempomat operation


These codes were cleared. After all other work is completed, I will recheck.



My meter is a rather new Klein Tools MM1000, with new batteries, leads in great condition. When I touch the leads together, I get a small reading and the buzz sound.


In a few days, the new sensors should arrive. They will be tested for continuity.


Big Thanks for following this thread and providing help!!!
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post #48 of 155 Old 23rd December 2018, 12:11 AM Thread Starter
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Today, front calipers are rebuilt. New pistons, seals, boots, guide rods and bronze guide rod bushings.


Tomorrow the rear calipers get the treatment.


Any suggestions for bleeding the master cylinder in the car that works? I would rather not mess with removing the MC to do a bench bleed. I bench bled it twice and I am not sure if all the air got out. I want to get this right this time around. I will do a web search on this...
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post #49 of 155 Old 23rd December 2018, 03:21 PM
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Quote:
Originally Posted by austrianvespaguy View Post
Glad I found this thread, as I'm experiencing VERY similar issues with the 2000 M5 that I just bought this week with a long, soft pedal, no improvement with bleeding, but also no warning lights. A question for you though, perhaps the strangest symptom that I'm experiencing is that the pedal is actually very firm and difficult to push while I'm trying to bleed the brakes, even with the caliper nipple open! Happily though, I actually have an extra ABS unit, albeit with a bad controller, but I'm just going to pull the hydraulic unit off the back of it and try swapping that out tomorrow to see if it improves matters.
So MAJOR success on my side! Indeed turned out to be the hydraulic unit half of the ABS system! I was able to determine this conclusively after I got plugged in with INPA. While cycling all of the ABS valves, got to the left-rear outlet and. . . no clicking!!! Removed the electronic front part and hooked it up to my spare unit and ran through everything again and all valves clicked properly, so then I went ahead and opened the lines, swapped in the good hydraulic unit, re-bled everything, and now brakes work properly again! Posting here in the hope this helps someone, key point being it was easy to hear which valve was non-functioning when cycling all of them in INPA!
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post #50 of 155 Old 25th December 2018, 06:48 PM Thread Starter
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HAPPY HOLIDAYS m5board!!!!

My kids are grown and live out of state so Xmas is quiet here now. We will be all meeting up in Virginia in a few days for my 70th birthday at a fine Three Star Michelin restaurant outside DC.

Life is good!


austrianvespaguy,

Good news that you got your Beast up and running right. Nice having a spare part to swap in.
When I ran both INPA and ISTA+ software, I could hear all the clicks and pump action so I don't think ABS/DSC unit is at fault. I am still waiting to receive the new wheel speed sensors (next week).

I included some pix of the MC.


Yesterday after getting the rear calipers rebuilt and installed and all calipers bled, I decided to take another look at the Master Cylinder (bleeding). I really wish BMW designed in a easily accessible bleed screw on the MC. There is not much space to reach the metal tube fittings (what were they thinking?). With the MC in the car, I was able to install bleed fittings on the port facing the drivers side and the port at the front end with hoses to the reservoir. When I pumped, I did see air bubbles and then none. I pumped, pumped and pumped many times. I wanted to be sure air is out. Then I did another power bleed of the calipers. With the car up on a lift, I pumped the brake pedal and held it, started the engine and I could push the pedal way down. Before I started the car, I could slightly move the calipers slightly left and right. After running the engine and working the brake pedal, there is no side to side play. There is some clamp up, but the pedal moves too far down. If there is STILL air in the system, I don't know where.


Still a problem somewhere...


I am looking for an answers to these questions on bleeding a Master Cylinder.

1. The M5 MC has three ports. Do I put bleeding kit fittings on all three ports and run all three hoses up into the reservoir and then slow pump the MC cycling the fluid around and any air out? My MC is brand new OEM $$$.


2. If this is done in a vice (bench bleed), doesn't air get in once the bleed kit fittings are removed? How much time do I have to hook up the metal tubes, or that is not an issue?

3. There is so little room to access the MC mounting nut on the passenger side of the MC, I had to have the reservoir removed. More time and major PITA! None of my web searches showed removing and replacing the MC and Booster as a unit and if ports are open, is fluid running out and air getting in?

IF I decide to remove the MC and the Booster as an assembly, how do I keep air out until this is reinstalled? I think it would take me fifteen or more minutes to position this and reconnect the metal tubes. There is not much room in there!!!

Long post, but I hope to get some answers and advice.

Thanks!!!!!!!!!!!!!!!
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