Clutch slave cylinder fell apart (?)

Hey gang -

I am in the middle of swapping out my chain and sprockets on my '96. Since I'm in Vermont (which is still knee-deep in winter), I have been taking my time to do this maintenance. I had removed the chain and sprockets about a month ago, and placed my order for a new RK kit yesterday.

With my renewed interest (and parts inbound), I took upon the task of cleaning up 10 years of chain grease from the SSSA and the front sprocket cover area.

When I got to the front cover, I noticed that the slave cylinder (which I had removed from the sprocket cover and stuck back on the pushrod) had "fallen apart" and drained the master cylinder of all of it's fluid. Essentially, the piston came out of the cylinder.

Do I have a problem here, or do I simply re-assemble and bleed it, and I'll be fine? This is my first-ever hydraulic clutch equipped bike.

 

The important thing with hydraulics is to keep them really, really clean (on the inside, that is), and to pre-lube the seal(s) with whatever hydraulic fluid will be used. Since the typical braking/clutch hydraulic systems have no filtration, any sort of grit will damage seals and surfaces, which creates even more grit that is also happy to recirculate and destroy whatever it can.

 

Just clean the bore and the piston if they are dirty/corroded. 0000 steel wool works well. Take the o-rings out before cleaning.

Be sure to clean the grooves real well before replacing the o-rings.

Lube liberally with brake fluid and push the piston back in. Make sure the piston stays even with the bore and does not get angled - it will cut the o-ring.

My method uses a big C-clamp.
The outside of the slave is protected from scratches by a thin board.
Then I use a socket just smaller than the piston. Turn the socket so the screw part of the C-clamp is inside the socket.
Then screw the C-clamp together. Reposition the socket as needed.
The socket keeps the pressure on the piston even so hopefully it will not get crooked.

Once the piston is in the bore, remove the socket and use the C-clamp to hold pressure on the piston. This will keep the piston from coming out. Not a lot of pressure is needed. Don't forget the board to protect the outside. A slave cylinder can be left like this for a long time. Even if you mistakenly use the clutch lever, the C-clamp will keep the piston inside the slave cylinder.

To refill the system use a mityvac to reverse bleed the system from the slave cylinder up. Basically, you will push brake fluid up to the MC. Once the slave is filled, it takes surprisingly little fluid to fill the lines. Cover the MC or you will have a 2' fountain of brake fluid spraying all over your bike.

Once filled, burp the banjo and enjoy your newly-filled clutch.

 

I finally go around to replacing the chain and sprockets.

It took a LOOOONG time and lots of bleeds, but I finally have some pressure at the clutch lever.

But it's been 6 months since I rode the bike, and I don't remember what it felt like. Currently, it's not mushy, but doesn't feel quite right.

I cleaned the bore of the slave cylinder several times, and reinserted the piston by hand. It did not require a c-clamp to install, and moved freely once re-installed.

Is there a way to check if the slave is doing it's job without starting the bike (because I don't have a battery currently)???

 

Yes. Put the bike in gear, pull in the clutch lever. If you can turn the rear tire, it works.

Note: It takes a good yank to get the rear tire started turning. You can do it with the left hand on the clutch and the right hand on the tire...

Or take it off the centerstand and put the bike in gear. If you can roll around with the clutch lever engaged, then it works.