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Front brake mystery


idigfunk
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Hi there,

 

  I'm having some problems with my front brake that I just can't seem to figure out and am hoping someone here can help.  I have a 2014 Sherco with a Braktec caliper and master cylinder.  Here is the issue:

The front brake is soft, but not always.  I tried regular bleeding procedures by pumping the brake, holding, releasing bleed valve, tighten, repeat.  I just put on a brand new caliper, hose and hardware connecting the hose to the caliper.  I reverse bled the system taking care to not have any air in it.  Once I did that, things were still quite soft and went back to regular bleeding process.  That helped quite a bit.  I did the bleeding process for a solid 20 minutes and the brake felt nice and firm.  Every time I pumped the brake, held, then released the bleed valve, I could see air bubbles coming up through the master cylinder upon opening the bleed.  They were very tiny.  Again, did this for about 20 minutes and it never stopped.  Eventually I put the cover on the MC.  Now the brake is spongy, to not working at random.  If the bike sits for a few minutes then I pull the brake, it will bottom out giving no braking power.  After a handful of pumps braking power will come back.  Sometimes if I'm hopping on the bike with the lever pulled in it will work at first, but a 10 seconds in the braking power goes out.  

 

Any thoughts?  More time bleeding?  Perhaps a rebuild in the master cylinder?  

Any help here would be extremely appreciated.  I'm growing tired of not being able to ride.

 

Thanks,

  Seth

 

 

 

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Thanks for the recommendation.  I rebuilt it, and backfilled the system from the caliper.  Immediately the fluid rolled up into the MC with far less pressure than what I was using before.  Sealed her up and the pressure is back to normal.  Thanks again.

 

 

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I am interested what have you used for back filling. I tried 150mm syringe and could not get enough of pressure from it for the oil to go through

Edited by Petr
typo
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I used a 60mm syringe.  Before I rebuilt the MC the pressure was so intense and it filled so slowly I couldn't tell if it was working.  Once I rebuilt, it still took some pressure but you could see the reservoir filling pretty quickly.  If it feels like the syringe is going to explode, something else is probably going on.  I also had to clean up the bleed nipple a bit.  Pulled it out and the hole in the bottom portion was kind of mangled.  

 

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After bleeding the brake so many times I decided to change the seals on M/C front brake. Unexpectedly easy job with extraordinary costs for a few pieces of rubber (£21!). It is now better and still a space for improvement ones everything gets seated.

When you did back fill, did you operate the handle at all?

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  • 5 months later...
 

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