Re: ST1300 Clutch Slave Cylinder Replacement
Hmmmm - now that is a very good question indeed BMacleod.
There is a seal in the little chamber or cavity in which the end of the CSC sits. The clutch pushrod runs through that seal and I don't know if it passes through a tube running through the crankcase or if it is simply in there with all of the engine oil and engine & tranny parts whirling around. I am sure that somebody on the Forum has been inside an ST1300 engine but I don't know who that might be because these things seem to be so darned reliable (except, of course, for my clutch slave cylinder issue).
It is worthwhile noting that the ST1300 clutch is wet - like nearly all modern bikes - which means that it actually runs IN engine oil (unlike manual transmission automotive clutches, which are nearly all dry), so I doubt that the presence of a bit of brake fluid would cause any slipping or other clutch problems. Similarly, there are around 3-4 litres of engine oil in circulation and I know that I didn't add more than a few ounces of brake fluid to my clutch the whole time my CSC was leaking - so the dilution ratio would be tiny if any occurred.
Finally, the clutch slave cylinder mounting incorporates a weep hole in the housing that is about 2-3 mm in diameter (1/8 inch) and so any leakage into that chamber will eventually run out of the weep hole rather than cause problems with the engine/transmission unit. BTW - that means that the gasket on the CSC mounting does not actually seal anything - because any liquids inside the CSC cavity (whether its clutch fluid or engine oil) will simply run out of the totally open weep hole. Incidentally, engine coolant (aka "water") pumps, including that on the ST1100 and ST1300, also incorporate weep holes for the same reason - so that engine coolant cannot get into the engine oil system if the coolant pump seal fails.
My experience with the CSC was that my initial problem was a very soft clutch which caused me to check the fluid level. The clutch master cylinder was just about empty. I topped it up and after a few days of riding (including several hundred km of combined highway and city miles), my clutch fluid level had dropped noticeably again and so I topped it up. The next morning, there was a spot of brake fluid on the floor under the bike about the size of a silver dollar (so the weep hole was working properly).
The other interesting thing is that when we took off the old CSC yesterday, there was perhaps a tablespoon of fluid still in the CSC cavity in the rear engine case which dribbled out onto the floor of my garage. During the time my CSC was leaking I had to top up the master cylinder twice - the first time, it was nearly empty and the second time, it was down to the lower limit. The total amount of fluid I added was actually pretty small - the entire system volume is small as you can see from the tiny amount of fluid we captured from the bleeding operation in my custom-made Heinz ketchup bottle fluid reservoir.
So...all that leads me to several conclusions:
1) if you catch a clutch fluid leak soon - it should not cause any problems with the engine itself:
2) any excess leakage will eventually wind up under the bike and you should see it on the garage floor;
3) but by then, you will likely have lost clutch actuation because the master cylinder will be empty - and that will force you to do something about it.
One thing to note: the ST1100 clutch slave system is completely different. Those lucky dogs have their CSC bolted to the front of the engine right on the clutch itself - and so changing the clutch slave cylinder would be (as the Brits say) a "doddle".
Anyhow, great question thanks!
Pete