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Offline Knobnose

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Brake fade
« on: December 18, 2018, 11:53:37 PM »
I started to experience brake fade at the beginning of my last trip - soft front brake lever with excessive travel. One pump gives proper lever feel.
I bled both front and rear resulting in no improvement. Called around to a bunch of N.Cal.BMW dealers but the nearest one that could look at it was in Las Vegas, so I made an appointment and rode there.
They had the bike ready in a couple of hours and told me the computer said the brakes were fine but they bled them anyway. I test rode it down the street, did a hard stop from 30mph and the lever came back almost to the bar. I asked them to give it a try and they agreed there was still a problem and took it back into the shop. They determined that the system was slowly losing pressure, ordered a new master cylinder and replaced it the next morning under warranty. The brakes felt fine so I continued East. Within a hundred miles or so the problem was back.
I lived with it for the rest of my trip by just giving an extra little pump which works  fine as long as braking can be anticipated but not so much in a emergency. I adjusted the lever all the way out which gives enough travel get the bike stopped without pumping but prevents my small hand from covering the brake.
Im taking the bike in  to a Bay Area dealer next month and wondering what I might suggest to them.There is a lot of ABS related plumbing under the seat and I wonder if that fluid gets changed with a normal bleed or if air or moisture could be lurking there. The fact that the brakes were fine for a while is puzzling. There in no evidence of a leak anywhere that I or the mechanic can see.
Any ideas?

Offline beech

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Re: Brake fade
« Reply #1 on: December 19, 2018, 06:46:34 PM »
The fluid in the ABS system gets changed with a flush that uses the shop computer or a GS-911. It is far more involved than a quick change.
On the other hand I have a friend with a different model BMW that had the same problem with the rear brake of that bike. Two dealers and three brake bleeds and the fade remained. We put the bike on the lift and gave the rear system a through bleed, I ran a pint of fluid through that system. About half way through that small bubbles started coming out. We worked on it until no more bubbles. The system has been fine since. Hard to convince a shop there is a problem. You did the right thing by quickly taking the bike back for a demo and letting them realize there is still a problem. Your brakes should not act like you describe of course. Sorry for your frustration. You may have to tackle this problem on your own to get the intensity of work needed.

Offline rogracer

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Re: Brake fade
« Reply #2 on: December 19, 2018, 10:04:52 PM »
You might try adjusting the driving modes (which alters ABS behavior and front/rear linking), as well as shutting off the ABS completely, and see if the problem remains.  If it changes or goes away it may point to an issue in the ABS valve body.  I wouldn't be surprised if there is some air in it.   When I asked the dealer at my last service if they cycled the ABS pump when they bled the brakes, they told me "no" they just "bled it".  I was kinda shocked by that but at least they were honest.  Even the GS-911 has the ability to cycle the valve body, so the dealer was lacking in this regard, and maybe yours was too.

Offline beech

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Re: Brake fade
« Reply #3 on: December 20, 2018, 09:53:00 PM »
I know most riders seldom get a chance or purposely activate the ABS while riding. I have a down hill dirt driveway and lock up my wheels at least once a month to get that ABS pump running. As the above post confirms, I don't think all dealers do the complete proper bleed sequence, much less clean and push back the pucks to get that trapped fluid out. There really is a lot to it. I use a GS911 and it is a big nanny looking over your shoulder to do a complete job.
« Last Edit: December 20, 2018, 10:07:52 PM by beech »

Offline Knobnose

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Re: Brake fade
« Reply #4 on: December 20, 2018, 09:57:56 PM »
Thanks for the suggestions, Ill report back next month. I think that part of the problem is that communication with the mechanic gets filtered through the service writer at large dealerships.

Offline Fistuk

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Re: Brake fade
« Reply #5 on: December 23, 2018, 09:01:50 AM »
I had a similar issue, but the breaks would not fade while riding. On occasion  I needed to pump the front lever a few times to get the pressure up on start up. After that - the lever would be fine and break feel would feel OK.

There was also some brownish goo clearly visible in the front break reservoir  - that would disappear when the break fluid got warmer (maybe it was sucked into the system)

The fluid was changed - two times in a row about 3 months apart and it solved the problem initially, but it would reappear. The techs at the garage told me that the second fluid change was 'deeper' process in which all of the fluid from the system (including the ABS pump) was flushed. The more involved process requires the shop computer to be connected.

The third time it happened, they could not get the pressure up to spec after flushing and they changed the front master cylinder (and flushed the system completely again). This seems to have solved the problem, although it only has been two months so it may be too soon to tell.

By the way - the bike is two years out of warranty but they still picked up most of the cost of the new master cylinder - without being asked to do so.

Offline rick_lee

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Re: Brake fade
« Reply #6 on: December 25, 2018, 04:34:32 AM »
Was just gonna post the same problem.  My bike is parked until I fix this, and it's about six mos. out of warranty.  I bought some Pentosin DOT4 LV today and will try to burp the system tomorrow.  Really hate this issue and don't want to pay to have what looks like a factory or design issue fixed.

Offline rick_lee

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Re: Brake fade
« Reply #7 on: December 25, 2018, 06:27:16 PM »
Well, I just did a traditional bleed, was extra meticulous, used a rubber mallet on the calipers, an air compressor suction attachment on the bleeders screws, and, well, it's a whole bike now.  That took at least 1-1.5" out of the lever travel.  Braking is super sensitive now and will take some getting used to.  I hope this does the trick and the problem doesn't come back for a while.

Offline rick_lee

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Re: Brake fade
« Reply #8 on: January 30, 2019, 05:50:41 AM »
And one month later and the lever is getting spongy again.  I did 1000 miles this past weekend, rode to SoCal and back.  I did a lot of lane splitting and stop and go in LA traffic.  Now lever is going farther down.  Not as bad as it was, but also not as good as it was after the last bleed.

Offline podders

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Re: Brake fade
« Reply #9 on: January 30, 2019, 04:21:21 PM »
Perhaps try rebuilding the front brake master cylinder, I had a quick google and found this.

https://www.motorworks.co.uk/vlive/Shop/Parts.php?T=6&Q=master%20cylinder%20repair&Sort=2

BMW appear to like chucking complete components on which must cost hundreds(at retail...) to solve the problem when in reality, its a few quids worth of rubber seals that actually need replacing, same as the common water pump issue.

I'm guessing that's because of time but its not the way to do it IMHO.

 


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