Clutch Master cylinder .....as usual need some advice!

[jfheath]

Should bleed it at the slave also to get rid of the old fluid....

Definitely. The old fluid in there isn't going to shift a great deal under normal operation. You want to be rid of the old.

So --- Top up the reservoir, bleed tube on the bleed valve on the top of the slave. Pump up the clutch lever - and hold it in. Open the bleed valve slightly and let the returning slave cylinder piston and the fluid pressure gently push the old fluid out. Close the bleed valve before it stops flowing.

Repeat. Pump the lever a few times to push in the slave piston - to mix any remaining old fluid with new inside the cylinder.

Repeat. Repeat. Keep an eye on the master cylinder reservoir - remember that this process is removing the volume of the slave cylinder every time. The reservoir will go down more quickly than normal.

If you just open the valve and pump fluid through, you are not getting the piston to move through the new fluid. This way, you eventually get a chamber full of new, holding the piston in, and then flushing the old out.

 

[SMSW]

Next time you bleed either the brakes or and the clutch , use a turkey baster to suck all the old fluid out of the master cylinder, refill it, and proceed.

If brake fluid is such a good paint remover, why do we spend big bucks on nasty poisonous paint removers with methylene chloride?

 

[Odie1]

Yeah - the clutch system was bled about 2 months prior, with the master cylinder being emptied with an aspirator (snot sucker!) first.

I kind of wonder if removing a bunch of the old "crud" is what led to the leak in the first place?

Odie1

 

[CYYJ]

Next time you bleed the brakes and the clutch , use a turkey baster to suck all the old fluid out of the master cylinder, refill it, and proceed.

I agree with the above, but with one caution: Don't ever operate the brake or clutch lever on the ST 1100 when the fluid reservoir is empty, because it can be a huge PITA to regain prime and get rid of an air bubble that will develop inside the piston of the master cylinder.

By all means, use a turkey baster, etc. to suck all the old fluid out, and even use a lint-free towel to clean out the bottom of the reservoir if you wish, but once you have done that, refill that reservoir (at least partially) with fresh brake fluid immediately, and then purge the last remaining bits of old fluid in the master cylinder piston by pumping new fluid through until the new fluid exits at the bottom (brake caliper, or clutch secondary master cylinder). Don't pump the master cylinder dry using the lever, because then you will get air into the master cylinder piston, lose prime, and it can be very difficult to get that air bubble out and get the fluid flowing again.

This problem seems to be unique to the two master cylinders on the ST 1100 handlebars.

Michael

 

[SMSW]

This problem seems to be unique to the two master cylinders on the ST 1100 handlebars.

Not completely true. Other bikes (brands) exhibit the same ability to hold onto air bubbles in the brake system despite repeated bleeding.