My Brake Pedal Feel is Kicking My Butt... - BMW M5 Forum and M6 Forums
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post #1 of 165 Old 28th November 2018, 11:48 PM Thread Starter
mr_g_bock
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My Brake Pedal Feel is Kicking My Butt...

On my 2002 M5 with the engine running, I can push hard on the brake pedal and it will sink almost to the floor. While driving I have to plan a head allowing extra distance for stopping. This is not 'the feel' that I had in the past.



I have searched and read many posts on this site and several other BMW sites along with general Google searches.


This is what I have done so far with out any success. I did a brake pad replacement along with a brake fluid flush. I have owned this car since new and the ABS/DSC system had not been flushed with new fluid. I procured both ISTA+ and INPA software to activate the ABS/DSC system. I was unable to fine a full, step by step procedure for dummies. Lacking such info, I poked around, activated various pumps and valves, pushed more brake fluid through the calipers (rr, lr, rf, lf). With the engine off, the brake pedal was good and hard. I start the engine and I could (with hard foot pressure) press the brake pedal almost to the floor. When I separated the brake boost vacuum hose, I could hear a good amount of air moving.



I bought a new master cylinder, did a bench bleed, and another master cylinder bleed once it was reinstalled into the car. Then more pressure bleeding and still the brakes feel lacking in bite. I took the car to a local foreign car shop that used Rheingold software to work the pump and bleed the system. There was no change in the pedal feel.


I even went so far to try a 'fix' that I read on a M3 board where you set the brake pedal to 80% depressed for twenty four hours to 'decompress' any air that might be captured in the fluid. This did not make any change.



I took the car out on the road and activated the DSC several times while making left, right turns and straight line stopping. I was able to lock up the brakes and it felt better somewhat. I did a final bleed but the again, with the engine on, the pedal still goes down a lot to the floor.


At this point I am at a total loss as to what to do next. I thought I addressed all of the possible causes, but there must be something else going on.



I am hoping someone on the site can shed some insight as to a fix for this problem.



A Huge Thanks In Advance. This is a great site!!!!!!
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post #2 of 165 Old 29th November 2018, 02:11 AM
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Quote:
Originally Posted by mr_g_bock View Post
On my 2002 M5 with the engine running, I can push hard on the brake pedal and it will sink almost to the floor. While driving I have to plan a head allowing extra distance for stopping. This is not 'the feel' that I had in the past.



I have searched and read many posts on this site and several other BMW sites along with general Google searches.


This is what I have done so far with out any success. I did a brake pad replacement along with a brake fluid flush. I have owned this car since new and the ABS/DSC system had not been flushed with new fluid. I procured both ISTA+ and INPA software to activate the ABS/DSC system. I was unable to fine a full, step by step procedure for dummies. Lacking such info, I poked around, activated various pumps and valves, pushed more brake fluid through the calipers (rr, lr, rf, lf). With the engine off, the brake pedal was good and hard. I start the engine and I could (with hard foot pressure) press the brake pedal almost to the floor. When I separated the brake boost vacuum hose, I could hear a good amount of air moving.



I bought a new master cylinder, did a bench bleed, and another master cylinder bleed once it was reinstalled into the car. Then more pressure bleeding and still the brakes feel lacking in bite. I took the car to a local foreign car shop that used Rheingold software to work the pump and bleed the system. There was no change in the pedal feel.


I even went so far to try a 'fix' that I read on a M3 board where you set the brake pedal to 80% depressed for twenty four hours to 'decompress' any air that might be captured in the fluid. This did not make any change.



I took the car out on the road and activated the DSC several times while making left, right turns and straight line stopping. I was able to lock up the brakes and it felt better somewhat. I did a final bleed but the again, with the engine on, the pedal still goes down a lot to the floor.


At this point I am at a total loss as to what to do next. I thought I addressed all of the possible causes, but there must be something else going on.



I am hoping someone on the site can shed some insight as to a fix for this problem.



A Huge Thanks In Advance. This is a great site!!!!!!

A couple of things come to mind.

First are the brake lines. They are rubber and as they age, they degrade. That allows them to flex. So before you get fluid to the calipers, the fluid first pushes the brake lines out before the fluid gets pushed where you want it to go. So get some steel braided lines. They have kits for our cars.

The other thing to check are the pads. Different pads can have different feel. What pads are you using? People here may have experience good or bad with the pads you are using.


Finally an old track trick. When you come in after a session, the brakes are obviously very hot. We would pull the wheels and just crack the bleeder for a split second. It seemed to help keep air out of the lines. I will let the engineers on here explain why!


One other thought. When you get ready to brake, give the pedal a quick medium tap, then immediately hit it normally. If the pedal firms up, you have air somewhere in the system and unlikely the ABS since that is closed off unless activated.

Regards,
Jerry

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Last edited by gsfent; 29th November 2018 at 02:15 AM.
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post #3 of 165 Old 29th November 2018, 02:15 AM
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I just had the same problem, did all the same things you did nothing worked, then I got a piece of tubing and a bottle with some brake fluid in it, tubing on bleeder screw other end submerged in the bottle, and did about 5 to the floor brake pedal pushes for each caliper, I now have a solid pedal!

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post #4 of 165 Old 29th November 2018, 04:05 AM
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Ceramic pads? They seem to have the spongiest feel of all the materials used for pads out there.

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post #5 of 165 Old 29th November 2018, 04:17 AM
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obvious dumb questions:

1)when you rebleed are you noticing air coming out? If so it it always the same corner?
2)notice any fluid near a bleeder or the pistons?

2001 E36/7 MRoadster
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post #6 of 165 Old 29th November 2018, 02:52 PM Thread Starter
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My apologies for not including more info that only occurred to me while in bed thinking all this over and over.


My car has 78k miles on it. When I was getting the ABS/DSC to activate, I could lockup the brakes in straight line braking.



The car does have SS braided lines and Akebono EUR683 and EUR681 Ultra-Premium Ceramic pads(low noise, low dust).


I do not see any fluid leakage at any places that can be viewed. And when I did the bleeding, no air bubbles are seen coming out at any of the calipers. I use a rubber mallet to bang on the caliper while bleeding to loosen/eject air bubbles (no bubbles cam out).



I will try the 'tap' and brake as suggested and the bleed & pump as suggested. Also I will try getting the brake pads hot to see if the bite improves.


Thanks People!!!! I will report back probably in a couple of days.
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post #7 of 165 Old 29th November 2018, 03:06 PM
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There is one thing I'm not clear about or may two.

1)If when you say it goes soft are you losing braking, ie I know you said you plan ahead but let's say you stop at 75% pedal position when it goes soft is same amount of braking at 75% or do you have to go 100% to get what was at 75%? If that makes sense?

2) Will it return to normal feel without you bleeding, ie sitting over night, after a few minutes blah blah blah blah

3) I lied I guess it's at 3 things... does pumping the brakes change anything?

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Last edited by Ferris; 29th November 2018 at 03:07 PM.
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post #8 of 165 Old 29th November 2018, 03:22 PM
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Quote:
Originally Posted by mr_g_bock View Post
When I was getting the ABS/DSC to activate, I could lockup the brakes in straight line braking.
Wait, do you mean you're getting ABS to activate and pulse the brakes properly, or do you mean what is written (that the brakes are literally locking up, skidding tires)?

Off topic perhaps a tad, but if you're not replaced them, check the condition of the flexible connections in the hard lines to the rear brakes which are subject to heat aging: #3 and #4 here.

Circling back to the driving experience...when you're going for maximum braking. Cruising along, and you immediately hammer the brake pedal and initiate ABS as fast as possible and hold it all the way to a complete stop -- how far down is the pedal during this full-on ABS stop?

I ask the above since during the 15 or so years of owning the M5, I can recall thinking the pedal travels too far when pressed hard with the engine running and sitting still in the garage (i.e. brake booster assisting), but I think in actual driving it wasn't an issue. Sadly, I sold the car this past summer, so I can't go out and experiment.

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Last edited by CSBM5; 29th November 2018 at 03:23 PM.
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post #9 of 165 Old 30th November 2018, 06:26 AM
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I would say it's the Akebono pads. Those things are terrible for pedal feel. To be honest, when I had them on my S62 swapped E38, they were downright scary. Try putting some Jurid front and Textar rears and see if they still feel spongy like that. Those are the OEM pads.

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post #10 of 165 Old 30th November 2018, 11:21 AM Thread Starter
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I will try and address the above questions:


When I say brake feel, I mean brake pedal travel. In a straight line at about 40 mph and I hammer the brakes, the pedal goes down about 75% before I feel the pads bite. I will have to press harder to get the DSC light to flicker on. With full foot force I can get the front wheels to lock up and I see some tire rubber smoke. I will have to test some more to see if I really feel the ABS brake pulses with DSC turned on. I always turn DSC off as I find it is too intrusive to my driving style (Sport is always on and was custom coded that way). I remember feeling the ABS pulses under hard braking at the BMW Driving Experience class, but that was a long time ago.



Under normal driving the ABS/DSC system should not have any affect on the pedal travel.



I understand what people are saying about 'pad feel' but I would think that should not effect pedal travel. The pistons have a set distance of travel, the hydraulics should be solid assuming no air in the system. I have pressure bled quite a few bottles of fluid through the system while not seeing any air bubbles nor fluid leaks.


Today and/or tomorrow I will reinspect, pressure bleed, bleed and pump brake pedal and report.


Thanks and I hope to put this to rest soon!!!
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