Clutch Master or Slave?

Whosaberg · Mar 23, 2015

OEM Magura clutch unit in my FE390. Master leaked. Replaced piston with OEM repair kit. Topped up with mineral oil. Bled. Still leaks.

How can I tell if it is the Slave O ring problem, or a bad master cylinder bore?

There's lots out there on this, but I am thoroughly confused and don't want to throw money without results.

Thanks Paul

fe390vt · Mar 23, 2015

slave leak

I have replaced 2 o-rings on the slave from my 390 and a friend's 450. Pretty sure that heat is the culprit.
Fan kit recommended all around to reduce engine heat.
viton oring... don't have part no... but its ends with 0021.
Google search clutch slave husaberg. Search engine on husaberg.org is kind of crappy. No offense to the admin.

berglsmerg · Mar 23, 2015

Run the engine for a rew minutes with the clutch hose disconnected from the master, if the slave is buggered the engine oil pressure will make a small flow out of the hose. Was the mc bore nice and shiny when you installed the piston ?

Check underneath the mc bar clamp for the bore size confirm the new piston is correct, the 167 mc comes in 3 flavours of bore size.

Whosaberg · Mar 23, 2015

Haven't had time to do any serious checks on it yet, but popped the top of the master reservior to see if there was any sign of muck, oil etc...none. The blood looks clear and slightly pink as it was when it came out. The piston for the master came from a non KTM dealer. On the bottom of my clamp it says 9.5. The new piston matched the old in everything, including the black and green orings on it.

Berglsmerg, I notice that your Magura rebuild kit

http://husaberg.org/mechanical/20073-2009-fe570-clutch-mc-rebuild.html

has two black orings...no green and contains the coregated rubber cover. Mined didn't, so I used the old one which pops off. Could that be the problem. Is that corregated rubber cover supposed to fit tight and contain fluid for lubrication of the piston? Could it really be that simple?

I did check the bore when I replace the piston: It was shiny and smooth to the touch. Cleaned it out. But didn't REALLY scrutinize it. Tomorrow!

Cheers guys. Paul

berglsmerg · Mar 24, 2015

The corrugated rubber is really only a dust cover to stop ingress of junk.

Did you lube the piston seals when you installed it?

The green seal does the work, the lower one is a back up in case of leakage.

Is it bled properly? The green seal needs pressure to energise the lip and push it against the mc bore.

Taffy · Mar 24, 2015

Whosaberg said:
OEM Magura clutch unit in my FE390. Master leaked. Replaced piston with OEM repair kit. Topped up with mineral oil. Bled. Still leaks.

How can I tell if it is the Slave O ring problem, or a bad master cylinder bore?

There's lots out there on this, but I am thoroughly confused and don't want to throw money without results.

Thanks Paul

what year is it?

Taffy

Whosaberg · Mar 24, 2015

Hi, Taffy. It's a 2010.

Whosaberg · Mar 24, 2015

Yes I lubed with mineral oil. Today, I noticed that, when cold, squeezing the lever there is a sucking sound coming from the piston/bore area. The corrugated rubber cover deforms (vacuum shrinks) as this happens. Wondering if this is normal or indicative of some sort of piston/bore blowby...? I have two O rings on order from KTM world in Georgia. A week until I get them. I will replace the oring in the slave and take stock after that.

Sounds like the magura slave is highly suspect with only one Oring. Many of the aftermarkets have two or more...Just hard to find them.

berglsmerg said:
The corrugated rubber is really only a dust cover to stop ingress of junk.

Did you lube the piston seals when you installed it?

The green seal does the work, the lower one is a back up in case of leakage.

Is it bled properly? The green seal needs pressure to energise the lip and push it against the mc bore.

Taffy · Mar 24, 2015

just check fella but certainly the 2009s were upgraded and maybe the 2010s as well! mine went and the new one I got had a different mechanism around the back side to operate the clutch. didn't do the job myself but recall checking it.

Taffy

Whosaberg · Mar 27, 2015

OK. Replaced the Oring in the slave cylinder with a viton replacement. Haven't ridden the bike yet, but on pulling the lever, there is still a very small leak from the master cylinder piston, despite putting in a new repair kit. Wondering if the bore is buggered. If so, what are my options...?

Clutch Master or Slave?

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