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M615 reservoir/master cylinder leaking??

mathematicsmathematics Posts: 452
edited September 2018 in MTB workshop & tech
My M615 front brake appears be leaking.

A few weeks ago fluid was seeping from the reservoir cap. So I removed the cap cleaned the rubber seal up reassembled and gave the system a good bleed. The brakes felt great. But after a couple of days I noticed brake fluid on the underside of the lever and it has continued to accumulate, its almost a droplet of fluid if I leave it 48 hrs. I can't see anything leaking from the reservoir cap, can they leak from the push rod are inside? If so is there any way to repair or stop this happening?

If I need to replace do I go M6000 or M7000 for the sake of £5?




  • 02GF7402GF74 Posts: 1,294
    In theory fluid can leak from any join in the hydraulic system.

    If it is not immediately obvious where fluid is coming from, then wipe the lever down and dust talc over it. Fluid will leave a trail.

    It sounds like the seals for the piston are going, are replacements available? If so, how much compared to a new lever?
  • If there's too much fluid in the system they will purge themselves, there is a little channel next to the reservoir.
    I found out after bleeding them, find fluid on the lever but after a while it cleared up.

    You normally find fluid underneath if that's the case (gravity!)and right on the rivet/bolt that holds the lever to the master cylinder body.

    If it's the main seal, where the piston pushes you can normally hear it squelching as you press the brake lever, you will hear a bubbling noise.
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