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#1 | spongy front breaks datum

Fri Jul 09, 2021 9:41 pm

Hi guys,

hope you can advise me here. It all started with front break lever being a spongy/soft. BMW changed master cylinder and flushed the system, but that did not help. Then I took it to independent garage where they also flushed the system, but not difference. As the bike has done over 36000 miles I have decided it is maybe time to clean front calipers and change pistons together with all seals. When I removed pistons it was obvious those rubbers were on their last legs, so they got changed plus new break pads as they need replacing too. When I put everything together again there was no massive change in "feel". I mean they break OK and I can stop when I need to stop, no issues there, it is just my feeling they just not that progressive/crispy as when the bike was new-ish. As master cylinder is still covered by the warranty and by extended warranty the bike is going back to the BMW garage soon. There is no leak of the fluid from the banjos or from the connectors. Just wondering if you have experienced something similar. The bike is sport se, 2015 model. Apparently GS bikes have got similar issue.

Thank you!

Martin

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#2 | RE: spongy front breaks datum

Sat Jul 10, 2021 4:14 pm

Zitat von matokc im Beitrag #1
Hi guys,

hope you can advise me here. It all started with front break lever being a spongy/soft. BMW changed master cylinder and flushed the system, but that did not help. Then I took it to independent garage where they also flushed the system, but not difference. As the bike has done over 36000 miles I have decided it is maybe time to clean front calipers and change pistons together with all seals. When I removed pistons it was obvious those rubbers were on their last legs, so they got changed plus new break pads as they need replacing too. When I put everything together again there was no massive change in "feel". I mean they break OK and I can stop when I need to stop, no issues there, it is just my feeling they just not that progressive/crispy as when the bike was new-ish. As master cylinder is still covered by the warranty and by extended warranty the bike is going back to the BMW garage soon. There is no leak of the fluid from the banjos or from the connectors. Just wondering if you have experienced something similar. The bike is sport se, 2015 model. Apparently GS bikes have got similar issue.

Thank you!

Martin

Generally, spongy would mean there's air in the system. Given how simple motorcycle brakes are, it's usually pretty easy to get it out, relative to cars, but here are some things to try. These have helped with cars though I haven't tried on bikes.

- Put the banjo bolts in wet, meaning apply brake fluid to the threads. Air can hide in them. Obviously this is a bit messy so make sure you clean up well.
- Consider vacuum bleeding and tap the caliper with a rubber mallet while it's under vaccum.
- You'll need a heavy bottle, but put the new brake fluid under a vacuum. Yes, I've seen fresh out of a new bottle have air dissolved in it. You'll know this because the fluid will bubble when it's put under a vacuum. It helps to shake the bottle when doing this.

2020 R1250RS

these members like the post: Sanemancured and Ray B

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#3 | RE: spongy front breaks datum

Sun Jul 11, 2021 12:23 pm

As the original post says the brake system has been flushed twice, I would be looking somewhere else perhaps.....
Have you had the brake lines themselves investigated and checked.
If any part of them expands under pressure, you will get the same symptoms.
Cheers

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Brake pad choices? � � Sportier R1200RS