Rear Brake Pedal Long Travel Problem?

Haroldsenior · Jun 12, 2016

DaveTez said:
I replied to another thread on the same subject yesterday:

My 2013 GS also developed the same problem, but I sold it before the issue was fixed!
However, my new 2016 2600 miler is not as good as I would like so I had a BM technician take a quick look.

He told me that its not a bleeding issue (you probably wont get any air out) but down to the fit of the rubber piston seals in their bores i.e. Very tight. (Cant quite remember the exact wording or figure out the logic!) sure someone will!

He went on to show me that by physically pushing the calliper against the disk & thus forcing the piston fully back into its bore that the brake pedal would have loads of movement. By activating the brake a few times the pedal was back to the top of its travel & firm again (try it!).
Another of his customers had admitted to not using the rear brake as much due to the brakes being linked, this had also resulted with the same problem.
I'll start using mine a bit more & see how it feels!

I don't doubt what the mechanic said nor that it worked but I can' t understand the logic. When using the caliper to push the piston in, the piston is being moved from the position it had last attained by normal operation. Yes it needs a few pumps to reverse the procedure but, surely, the piston ends up in the position it was before being pushed in by the original caliper action? Or have I missed something.?
My rear brake also suffers from the fault and may I also confirm against using the threaded link to adjust the travel.

Fullchat · Jun 12, 2016

Dont know whether this is of any relevance but the Triumph Sprint 1050s have an issue with the front brakes which caused the feel to become a bit 'woolly' after a while. The cure was to exercise the front pistons by removing the pads and extending piston travel then pushing back in a few times. Also a clean of the exposed piston. Normal feel returned to the lever. This could be cured by fitting pistons from the 675 Daytona which had a different coating on the pistons. So presumably there was some sort of stiction on the piston which interferred with its operation.

Deleted account 220214001 · Jan 18, 2021

Been doing a bit of research and there are two possible solutions:

1) It's possible that the issue is, as mentioned above, with the design of the master cylinder (MC). The solution, then is to change it but that also requires a new pushrod as well and some slight modification to the heelguard in order to accommodate the larger bolts. In some cases I have even read that some BMW dealers will be shamed into replacing it at their expense. Good luck with that!!! Below is a picture of the part with the number in case anyone is interested.

2) Instead of the £23/tin fluid approved by BMW some have had success with the £49/tin CASTROL DOT4 which has a higher temperature resilience and somehow seals better.

Sergio Afonso · Jan 18, 2021

My wife's bike 1200gs (2014), had this problem 2 times, first time it was about 4 years old, and second time it was last year, the 2 times it was the rear master cylinder, (the funny thing is she never uses the foot brake

I have a GSA with the same age with more or less more 3000Kms ( 90.000Kms +/-) it never had this problem and i use the rear brake all the time

unicycler · Jan 18, 2021

had the same problem with last 3 GS bikes. Fitted GSA brake pedal and keep flip part down all the time. Every time i change bike i keep the brake pedal and fit to new bike.

Rear Brake Pedal Long Travel Problem?

Haroldsenior

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Fullchat

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Deleted account 220214001

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Sergio Afonso

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