1198 clutch getting airbound

1125 Views 5 Replies 4 Participants Last post by vfrman, Jul 23, 2015

gunther19820

Discussion Starter · Jul 20, 2015

Hey guys, bike has a new clutch in it, plates, basket, pressure plate, springs.... Dealer installed last year. Clutch itself is fine, doesnt slip, etc.

But the system keeps getting airbound, my trackday on Friday I started having trouble getting neutral, then had 2 false gears, 1 putting me off course.

So my question is, where are the systems likely to pull air from? I would say the slave, but if its pulling air, wouldnt it also leak fluid? I have no leaks in the system, and it is not airbound when I bleed it (obviously)

Any ideas? Any sort of bench test procedure for the slave?

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papawle

· #2 · Jul 21, 2015

From what i found its the oem slave.

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Shazaam!

· #3 · Jul 21, 2015 (Edited)

It's not air in the system — it's excessive water in your hydraulic fluid. Water boils at 212°F which creates pockets of compressible water vapor (steam) that behaves like air bubbles. Change your fluid.

You need to get rid of ALL the water that has puddled in the slave cylinder. This requires removing the line from the slave, remove the slave from the engine casing, and inverting it to assure that all water is removed down in the lowest point of the slave/system. Water is heavier than hydraulic fluid so it sinks to the lowest point. Use a blast of compressed air to assure that the slave is completely dry before refilling with fluid and reconnecting the line.

Then bleed the air from the system, preferably from its high-point. Newer bikes have a factory bleed nipple located inside the fluid reservoir to make it easy. Older bikes like the 916 are notoriously difficult to bleed because the factory bleed nipple is located above the system low-point on the top of the slave cylinder. If you replace the banjo bolt at the master cylinder on earlier models with one with a bleed nipple it’s much easier to bleed air from these systems.

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gunther19820

Discussion Starter · #4 · Jul 22, 2015

Thanks Shazaam.
So this raises a new question- what fluid are you putting in? I assume there is a different boiling point between DOT3 and DOT4..

my clutch master is radial, so I will benchbleed it before putting system back together.

Any serviceable pieces to the slave I need to be concerned with- IE any sorts of seals that will need to be replaced when I brake the slave loose?

This is the perfect time to install the new clutch line I have floating around

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Shazaam!

· #5 · Jul 22, 2015

Fluids that meet the DOT 4 standards have a slightly higher wet and dry boiling point than DOT 3 fluids. There's no need to use expensive high temperature brake fluids in the clutch system. Buy what's on sale. The important thing is to change the fluid regularly to remove the absorbed water.

There are some fluids that don't turn black when used with aftermarket slaves such as Valvoline SynPower, ATE Super Blue, Galfer Super DOT 4 and Motul RBF 600.