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Discussion Starter #1
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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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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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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Ceramic pads? They seem to have the spongiest feel of all the materials used for pads out there.
 

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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?
 

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Discussion Starter #6
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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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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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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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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Discussion Starter #10
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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Ok, good luck on further evaluation - hope you get this sorted out soon.

Couple of thoughts: (1) there should be no tire lockup on maximum braking. It doesn't matter if DSC is on or off, ABS stays fully functional (unless you pull its fuse). Hence on a max effort braking action, you should quickly feel the pedal pulsing as ABS is active prevent one or more wheels from locking up. The tires will likely lay down a light rubber trail since they are being held to a rotation speed less that car velocity by a small amount, but it's unlikely to yield much if any tire smoke. So, no skidding, locked up wheels -- that shouldn't be happening. If you're getting tire lockup, other problems are at work.

(2) What blackknight is referring to above is that pads with a low coefficient of friction (essentially all ceramic low dust pads unfortunately) require more brake piston force to provide the same level of braking action as a "normal" pad. Hence while a set of OE type pads might require say 20lbs of brake pedal force (and the small amount of pedal travel that would entail) for a serious stopping event, the ceramic pads might need 40lbs of brake pedal force for the same braking action. The pedal travel required to create that level of force is of course a good bit more. I think that's what Paul was referring to.

It's almost impossible to relate how much of a difference brake pad coefficient of friction makes on the E39 M5; much more so than other cars I have experience with. With Stoptech BBK up front on my M5, I could run the Centric ceramic pads and be ok with the braking action, more or less. With the stock front brake setup, the same pads created a less than desirable brake pedal response (with more pedal travel required). I sold my car this summer, and I think the new owner was ready to change out those new pads right away. :) Dust be damned!

Regards,
Chuck
 

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Discussion Starter #12
Unfortunately I had to take care of some work at our rental property and did not have the energy to work on the Beast. I hope to work on the M5 on Monday and report my findings or success...
 

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Discussion Starter #13 (Edited)
Yesterday I was able to spend some time on the Beast.
I ran the INPA program and activated all of the valves, pumps, etc... presented.
Then I ran ISTA+ program and found how to select the DSC 57 unit venting and pump activation while pressure bleeding via the 'continue' button. Need to select 1 and continue, then 2 and continue for RR, RL, FR, FL corner.

No air bubbles were seen coming out so I have to think my whole brake system is purged of air.

Went for a test drive and some drifting to work the DSC. The pedal travel still goes deep to stop. I found out about another large empty parking lot with only one light pole. I will go there and have some fun.

When I changed out the brake pads, I threw them in the trash. I will see about getting the Jurid and Textar pads and try them and see if the pedal travel is better/shorter.

In the past I used Axxis Ultimate (for the longest time they squealed like Banshees) and also Ferdo pads that felt right but with some brake dust.

To be continued...


I want to add that after looking up price and availability on the Jurid and Textar pads, I see they are both using Ceramic pad compounds. Now I am unsure if these will have the same issues as I have with my current pads????


Does anyone else have first hand experience info to add on this or other brands to try?
 

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Discussion Starter #14
I would like to ask a question pertaining to bench bleeding the master cylinder. The master cylinder has three ports, one on each side of the cylinder bore and a smaller size at the far end. I bought the cylinder bleeding kit a a local auto parts store. I fitted the port fittings and hoses that then ran into the reservoir. With a full reservoir, I gently pumped the plunger and pumped brake fluid till no bubbles were seen going into the reservoir. Is this correct? All three lines pushing fluid back to the reservoir?



After the master cylinder was bolted to the booster and installed into the car, I reinstalled the bleed fittings and hoses to the reservoir and pumped more fluid through just to be sure before reattaching the metal brake lines (all three).


Did I do anything wrong here? Please advise.


Thanks!!!!!!
 

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I have the akebonos, that's not the problem, keep firing the parts cannon at it, or do what I suggested in my first post,
 

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Personally, I do not and have never liked ceramic pads. They're just . . . weird. My opinion, of course.

I like the Jurid pads very much. Economical and simple choice. If you're trying to troubleshoot a problem, try and remove variables. The Jurid pads are pretty reliable in that regard.

I've used Pagid Red (Bavarian Autosport house brand) and they worked well.

I really, really like the Carbotech 1521 Bobcat pads. They're comparably expensive and yes, they're a ceramic formulation but they're very nice.

The Centric Post-Quiet Semi-Metallic pads I just installed in my X5 are really great. Very sure stopping in all temperatures, zero noise and not as much dust as I would expect. In fact, probably less dust than the OE pads on there before which were also very good.
 

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OP - Do you know the status of the calipers? My M5 suffered from poor pedal feel that was somewhat improved by ss lines, mutiple rounds of bleeding, etc. I still was not happy with the pedal feel, so I decided to rebuild the brake calipers. I found the piston seals bad on the rear two calipers and the piston was rusted on one of the front calipers and the seal was destroyed. I never had any external indications of brake fluid leakage, but after replacing all the pistons and seals, my pedal feel improved to where I would consider it normal. I had the same problem you're reporting, brakes would feel solid with the engine off, but the power assist from the booster with the engine running was enough to make the pedal mushy.

I think rockauto has the caliper seals and freshly chromed pistons for about $30/corner so that might be something to look into. It seems you've tried everything else.


I'll second the Carbotech 1521 pads if you're looking for a street pad. It looks like OP does a bit more that just street driving, though. They took a few hundred street miles for the pedal feel to solidify, but for a street pad I really like them. Pedal feel is good, low dust and low noise and surprisingly good rotor wear. The only real world problem I have discovered is the pad has relatively low tolerance for dust/sand, so they are not ideal for cars that operate in sandy soil areas. The pad is hard enough that the sand particles will embed in the surface, but not sink in and will quickly groove brake rotors and become noisy.
 

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Discussion Starter #18
Well I just came from the garage and want to report in....


I set up my Motive Power Bleeder, full reservoir, wife watching the brake fluid catch bottle while I started up the engine. I opened the bleed screw and pumped the brake pedal ten times full stroke (the master cylinder is new). At the right rear caliper, she said she saw some bubbles at first, then just clear fluid. The I closed the bleed screw. I did this at all four corners ( ten strokes of the pedal) while keeping the reservoir topped up. Then while the engine is off, I pumped the pedal maybe five times and then held it. I then started the engine and the brake pedal went right down to the floor.


From what I had read earlier, the brake pedal should have only dropped maybe a quarter inch, not to the floor. Am I right in suspecting that the brake booster or vacuum line to it could be bad? Any tips on diagnosing a vacuum leak for this? Pulling the master cylinder and booster again does not make me happy along with re-bleeding the whole system if this is the problem.


All comments and suggestions are very much appreciated!!!!!!!!
 

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Well I just came from the garage and want to report in....


I set up my Motive Power Bleeder, full reservoir, wife watching the brake fluid catch bottle while I started up the engine. I opened the bleed screw and pumped the brake pedal ten times full stroke (the master cylinder is new). At the right rear caliper, she said she saw some bubbles at first, then just clear fluid. The I closed the bleed screw. I did this at all four corners ( ten strokes of the pedal) while keeping the reservoir topped up. Then while the engine is off, I pumped the pedal maybe five times and then held it. I then started the engine and the brake pedal went right down to the floor.


From what I had read earlier, the brake pedal should have only dropped maybe a quarter inch, not to the floor. Am I right in suspecting that the brake booster or vacuum line to it could be bad? Any tips on diagnosing a vacuum leak for this? Pulling the master cylinder and booster again does not make me happy along with re-bleeding the whole system if this is the problem.


All comments and suggestions are very much appreciated!!!!!!!!
Either your booster is bad or one or more of your calipers needs to be rebuilt. Start with the booster unless your calipers are high mileage, in which case they probably should be rebuilt anyway. I'm betting it is the booster. Not an entirely unusual phenomenon.

--Peter
 

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[ set up my Motive Power Bleeder, full reservoir, wife watching the brake fluid catch bottle while I started up the engine. I opened the bleed screw and pumped the brake pedal ten times full stroke (the master cylinder is new). At the right rear caliper, she said she saw some bubbles at first, then just clear fluid. The I closed the bleed screw. I did this at all four corners ( ten strokes of the pedal) while keeping the reservoir topped up.]

Are you closing the caliper bleed screw before releasing the brake pedal?
 
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