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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 07-03-2012, 06:08 AM
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Mark K Mark K is online now
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Weird brakes behavior

Disclaimer: I did a search and this has nothing to do with two relatively recent threads about brake pedal being hard on a startup.


Saturday, three days ago, I went to a car wash. I have no clue if this is relevant or not, but I mention it anyway. Up to that point and for about 35 kmiles the brakes worked perfectly fine, same pedal travel, same force required to obtain same amount of deceleration. When I got out of the car wash, the brakes worked fine but the pedal travel was half of what it used to be and I brushed it off with wet brakes. I drove for 5 miles in high heat and everything is still the same. At this point I tried 2-3 emergency stops and pedal travel before the ABS kicked in is about half of what it used to be and effort to engage the lock is much higher.

I do know that there are couple of days every 6 months when I just can't drive properly to save my life, so I parked the car in the garage and waited until Sunday. Did my usual drive in the twisties on Sunday and brakes are the same as day before, with such a short travel it was very hard to do any rev-matched downshifts - it sucked big time. Now I'm convinced it is not me and I decide to wait until Monday for a final test - that's when my wife will drive the BMW to work. Mind you, brakes performed perfectly fine, stopping was never a maybe, so I was fine with her driving it in traffic at 45 mph max for 4 miles to work without telling her anything in order not to influence feedback. Sure enough, she immediately noticed it.

OK, now a kicker. Yesterday (Monday) we went to movies and I drove the car. Same thing with brakes and during the dinner we decided she'll take it to a dealership on Thursday since dealer is 0.5 miles from where she works and she doesn't need a loaner. I will call today and arrange the service visit. Driving BACK home from the theater, the brakes started feeling different, almost back to normal. Now I try couple of rev-matched downshifts and it felt perfectly normal. This morning I drove it and it is basically back to normal, can't tell the difference.

I have absolutely no clue why the brakes felt and behaved like (I imagine - still have to try that one) they would be on a race car - i.e. short travel, high(er) effort, perfect modulation still possible and normal stopping distances. They did that for about 2 1/2 days and now back to normal.

Any suggestions?

Thanks in advance.
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2011 E92 335i 6MT ZSP ZCW (ED May 17th 2010)

2013 118d BMWNA Special Edition. Black on black cloth (yay!), 5 door hatchback, 140hp diesel. Special edition items: factory debadge| "VW", "Golf" and "TDI" badges factory applied | MT | Standard go flat tires | Spare tire (yay!) | No moonroof (yay!) .
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  #2  
Old 07-03-2012, 06:29 AM
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Your brake assist may be on its way out.

DSX is your man for this.
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  #3  
Old 07-03-2012, 06:41 AM
Michael Schott Michael Schott is online now
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Brake travel should be very consistent and is solely based on pad thickness. Maybe this has to do with the brake drying system or the fade compensation system.
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Old 07-03-2012, 07:04 AM
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Quote:
Originally Posted by ///M-ratedE90 View Post
Your brake assist may be on its way out.
DSX is your man for this.
Yes, I'll wait to see what DSX has to say about it. My main problem now will be to explain to a dealership that something actually happened since they are back to normal operation.

Quote:
Originally Posted by Michael Schott View Post
Brake travel should be very consistent and is solely based on pad thickness. Maybe this has to do with the brake drying system or the fade compensation system.
That's what I thought as soon as I drove off from the car wash. But after 2-3 emergency stops, they were dry for sure especially in 100 degree weather. Do you know when and how would fade compensation kick in? Thanks.
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2011 E92 335i 6MT ZSP ZCW (ED May 17th 2010)

2013 118d BMWNA Special Edition. Black on black cloth (yay!), 5 door hatchback, 140hp diesel. Special edition items: factory debadge| "VW", "Golf" and "TDI" badges factory applied | MT | Standard go flat tires | Spare tire (yay!) | No moonroof (yay!) .
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  #5  
Old 07-03-2012, 07:18 AM
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Quote:
Originally Posted by Mark K View Post
Yes, I'll wait to see what DSX has to say about it. My main problem now will be to explain to a dealership that something actually happened since they are back to normal operation.



That's what I thought as soon as I drove off from the car wash. But after 2-3 emergency stops, they were dry for sure especially in 100 degree weather. Do you know when and how would fade compensation kick in? Thanks.
When the pads wear, more fluid is pumped into the brake caliper to adjust for the change in thickness, so the pedal travel will stay the same regardless of pad wear. The fade compensation would be the same, you will essentially see little change in feel, but the assist will squeeze harder for the same pressure from your foot.
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  #6  
Old 07-03-2012, 08:35 AM
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Quote:
Originally Posted by ///M-ratedE90 View Post
When the pads wear, more fluid is pumped into the brake caliper to adjust for the change in thickness, so the pedal travel will stay the same regardless of pad wear. The fade compensation would be the same, you will essentially see little change in feel, but the assist will squeeze harder for the same pressure from your foot.
OK, this is definitely not what happened - the feel changed a lot.

I asked about what triggers fade compensation because of this far-fetched scenario:

a) whatever sensor (I thought it was windshield wipers, but not sure at all if that's the only thing working there) tells the car brakes need drying. And keeps telling it that all the time. This is the only scenario I can think of where car wash has something to do with it. It's hard to dismiss it since it started immediately as I drove off their driveway.

b) pads are in contact with rotors to dry them out creating the excessive heat. Of course, at the time I never thought to at least put my hand on the rim to see if there might be excessive heat coming from rotors so I don't know that for sure.

c) fade compensation (if they work on pads/rotors temp) thinks I'm in brake fade danger and applies overboost. Since there's nothing wrong with brakes and pedal wouldn't go to the floor in the first place, the travel is now shorter and brakes feel hard. Which might have made me feel like I need more leg force to stop but that wasn't really the case if measured properly in Newtons.

Of course, if I knew I was right, I'd be car mechanic

Thanks for the replies.
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2011 E92 335i 6MT ZSP ZCW (ED May 17th 2010)

2013 118d BMWNA Special Edition. Black on black cloth (yay!), 5 door hatchback, 140hp diesel. Special edition items: factory debadge| "VW", "Golf" and "TDI" badges factory applied | MT | Standard go flat tires | Spare tire (yay!) | No moonroof (yay!) .
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  #7  
Old 07-03-2012, 01:31 PM
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DSXMachina DSXMachina is offline
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Quote:
Originally Posted by Mark K View Post
Disclaimer: I did a search and this has nothing to do with two relatively recent threads about brake pedal being hard on a startup.


Saturday, three days ago, I went to a car wash. I have no clue if this is relevant or not, but I mention it anyway. Up to that point and for about 35 kmiles the brakes worked perfectly fine, same pedal travel, same force required to obtain same amount of deceleration. When I got out of the car wash, the brakes worked fine but the pedal travel was half of what it used to be and I brushed it off with wet brakes. I drove for 5 miles in high heat and everything is still the same. At this point I tried 2-3 emergency stops and pedal travel before the ABS kicked in is about half of what it used to be and effort to engage the lock is much higher.

I do know that there are couple of days every 6 months when I just can't drive properly to save my life, so I parked the car in the garage and waited until Sunday. Did my usual drive in the twisties on Sunday and brakes are the same as day before, with such a short travel it was very hard to do any rev-matched downshifts - it sucked big time. Now I'm convinced it is not me and I decide to wait until Monday for a final test - that's when my wife will drive the BMW to work. Mind you, brakes performed perfectly fine, stopping was never a maybe, so I was fine with her driving it in traffic at 45 mph max for 4 miles to work without telling her anything in order not to influence feedback. Sure enough, she immediately noticed it.

OK, now a kicker. Yesterday (Monday) we went to movies and I drove the car. Same thing with brakes and during the dinner we decided she'll take it to a dealership on Thursday since dealer is 0.5 miles from where she works and she doesn't need a loaner. I will call today and arrange the service visit. Driving BACK home from the theater, the brakes started feeling different, almost back to normal. Now I try couple of rev-matched downshifts and it felt perfectly normal. This morning I drove it and it is basically back to normal, can't tell the difference.

I have absolutely no clue why the brakes felt and behaved like (I imagine - still have to try that one) they would be on a race car - i.e. short travel, high(er) effort, perfect modulation still possible and normal stopping distances. They did that for about 2 1/2 days and now back to normal.

Any suggestions?

Thanks in advance.
When hydraulic/mechanical things go whacky with brakes they never fix themselves and seldom come, stick around a couple days, and then disappear. That leaves us with an electric/electronic fault in one of five areas.
I think an ABS related problem is the least likely, also as unlikely is a fault in the proportioning module. I think you had a glitch in one of the three standard safety systems built into your brake system.
You know that your E92 has fade sensing which helps reduce the amount of pedal pressure needed to effect a safe stop as the brakes heat up. A malfunction in this system could result in the symptoms you describe but I've got a better guess.
The second possibility is a fault in the pad positioning system which pops your pads out a fraction whenever you suddenly release the accelerator. The logic is that you've detected a road hazard, popped your foot off the accelerator and are about to hard brake. Anticipating that, a nanny prepositions the pads for hard braking. But I don't think that's your problem either. Here's my w.a.g.*
I don't believe in coincidences, I think your trip to the carwash is the cause of your problem.
Whenever your wipers are on a brake module in the coupe applies the brakes very softly in a timed sequence. The purpose of this application is to wipe the rotors and keep them warm enough to evaporate any moisture. I'll bet you ran your wipers at some point during or after the carwash. That began the rotor wiping sequence and for unknown reasons the process didn't stop. Heat built up and caused the anti fade system to kick in and that's what resulted in all your symptoms. Why? Damned if I know, but that's what I get paid the big bucks for figuring out. BMW should do it for free. Good luck with that.

*wild donkey guess
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  #8  
Old 07-03-2012, 06:00 PM
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Quote:
Originally Posted by DSXMachina View Post
Here's my w.a.g.*
I don't believe in coincidences, I think your trip to the carwash is the cause of your problem.
Whenever your wipers are on a brake module in the coupe applies the brakes very softly in a timed sequence. The purpose of this application is to wipe the rotors and keep them warm enough to evaporate any moisture. I'll bet you ran your wipers at some point during or after the carwash. That began the rotor wiping sequence and for unknown reasons the process didn't stop. Heat built up and caused the anti fade system to kick in and that's what resulted in all your symptoms. Why? Damned if I know, but that's what I get paid the big bucks for figuring out. BMW should do it for free. Good luck with that.

*wild donkey guess
HAH! I guess I should be a car mechanic after all

Thanks, DSX. I have one final question for you ... do you know for certain that windshield wipers are the only thing that tells the car brakes need "wiping" or could there be a sensor somewhere else? You see, I didn't activate wipers, but guys doing the interior cleaning might have done that - I wasn't watching them closely.
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2011 E92 335i 6MT ZSP ZCW (ED May 17th 2010)

2013 118d BMWNA Special Edition. Black on black cloth (yay!), 5 door hatchback, 140hp diesel. Special edition items: factory debadge| "VW", "Golf" and "TDI" badges factory applied | MT | Standard go flat tires | Spare tire (yay!) | No moonroof (yay!) .
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  #9  
Old 07-03-2012, 06:12 PM
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DSXMachina DSXMachina is offline
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Quote:
Originally Posted by Mark K View Post
HAH! I guess I should be a car mechanic after all

Thanks, DSX. I have one final question for you ... do you know for certain that windshield wipers are the only thing that tells the car brakes need "wiping" or could there be a sensor somewhere else? You see, I didn't activate wipers, but guys doing the interior cleaning might have done that - I wasn't watching them closely.
As you know, there is a light sensor built into the back of the irv mirror which determines when there is a given amount of rainfall on your windshield. This info is used to activate the delay function of the wipers when the driver selects that option.
It's possible that the information could be relayed to the brake control module whether the driver activates the wipers or not. I don't know.
Some car washes, like quick oil change centers, have an addtional profit center in add-ons like scented pine trees and windshield wipers. Maybe the wash crew activated your wipers to see if they could sell you a pair.
BTW, no self respecting first time owner of a Bimmer takes it to a car wash. I hope you have learned a lesson. Next time your angel eyes could self activate and start winking at oncoming drivers.
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  #10  
Old 07-04-2012, 05:28 AM
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Mark K Mark K is online now
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Originally Posted by DSXMachina View Post
BTW, no self respecting first time owner of a Bimmer takes it to a car wash. I hope you have learned a lesson. Next time your angel eyes could self activate and start winking at oncoming drivers.
Now, THAT would be cool. Messing with my brakes - totally uncool.

Thanks.
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2011 E92 335i 6MT ZSP ZCW (ED May 17th 2010)

2013 118d BMWNA Special Edition. Black on black cloth (yay!), 5 door hatchback, 140hp diesel. Special edition items: factory debadge| "VW", "Golf" and "TDI" badges factory applied | MT | Standard go flat tires | Spare tire (yay!) | No moonroof (yay!) .
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