Clutch master cylinder leaking?

[dcarver]

2006 with almost 250k miles. 

Clutch goes soft overnight. No visible leakage at slave or mc fittings or along hose.

Possible it's leaking back through the piston seals?

Multiple lever actuation restores pressure, but not completely. 

Bleeding restores 100%.

Once done, it holds pressure as long as bike is ridden.

Academic question really, I bought a 4,300 mile used MC from eBay.

Just wondering if piston seal leak by is a good guess.

[NTXFJR]

Sounds like it could use a new piston seal kit. Reservoir is full?

[raYzerman]

If you are losing fluid out of the reservoir, then there may be some leaking past the seal of the Slave Cylinder.... with that many miles, I'd slip in a new master cylinder kit anyway......
BTW Mr. Carver, there is an ancient PM in your inbox... is your inbox full?

[dcarver]

If you are losing fluid out of the reservoir, then there may be some leaking past the seal of the Slave Cylinder.... with that many miles, I'd slip in a new master cylinder kit anyway......
BTW Mr. Carver, there is an ancient PM in your inbox... is your inbox full?

Reservoir fluid remains full at all times. I replaced the slave cylinder earlier, back to the 2006 with longer throw. The clutch going soft issue happened on both the 2006 and later model slave cylinder. Pretty sure it's not leaking past the slave cylinder seal.

I found a 4,300 mile used master cylinder for cheaper money than the rebuild kit so I'll give it a shot first.

Ray, PM sent back at yah!



Forgot to add that now the damn thing appears to be holding pressure..

[raYzerman]

On my project bike, after I re-primed the master cylinder (bled at the upper banjo), I had a heck of a time getting rid of a bubble... checked everything, then took a syringe and reverse bled it... the air bubble went to the top, done, all good.. Maybe your bubble eventually got to the top...