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Brake Master Cylinder Leak


Jan Randall

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There is no pressure increase in the reservoir when using the brakes, as opposed to being stationery, so possibly more likely that it is leaking from the cap during cornering.

My 2015 R400 leaked from both the brake MC cap, and more so from the clutch cylinder, during a track day earlier this year. I replaced the nasty standard cap on the clutch cup with a Girling one, which seals better. The brake cyl leak was solved for me by tightening a little more but  I have cable tied a piece of paper wipe around the joins of both just in case. So far there have been no more leaks, but I'll only stop using the wipe once I'm really sure. it shows leaks very clearly but stops the fluid getting everywhere.

I understand these leaks are not uncommon, especially from the standard clutch cap and on track. 

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Thanks Scott. I have been through the same procedures as you already. However I think it is the joint between the reservoir and the metal at the front as when I push down this weeps slightly, but not enough to drip. I think it ought to be capable of repair if I can remove the metal pins that hold the reservoir in position such that I can reuse them and find out what the red sealant is the manufacturer used. I hope yours turns out to be only the top.

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Hi Jan,

Sorry to hear of your troubles. 

I've not had my brake m/c apart (unlike my clutch m/c!), so don't know what's in there.  My guess would be that there'll either be a couple of O-rings between the reservoir and the metal body, or a gasket and (possibly) sealant.  I don't know who makes these m/cs but you could try asking CC.  If it has O-rings, you might get suitable replacements from somewhere like Eriks.  There's a Service Centre near you.

When you say "metal pins", do you mean they would be difficult to remove?  I ask as my 2008 brake m/c has two Phillips screws holding the reservoir on.  It looks pretty much like this one.

Of course, the alternative point of view says that any leakage problem with brake hydraulics warrants new parts.

Good luck -- hope to meet up again at Castle Combe sometime.

JV

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