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Discussion Starter · #1 ·
If my clutch master cylinder reservior does not reduce fluid during bleeding (using a hand vac pump) from the slave cylinder bleed valve but does create some sucking sound coming from the master cylinder; does that mean the mc is bad?

Thanks for the help.
 

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Was the clutch working before you bled the system? What if you connect a hose to the bleeder fitting and bleed without vacuum...just pull in the clutch lever...does the fluid level change then?
 

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Discussion Starter · #3 ·
Was the clutch working before you bled the system? What if you connect a hose to the bleeder fitting and bleed without vacuum...just pull in the clutch lever...does the fluid level change then?
The clutch was not working well. Sloppy tension and could not get in and out of gears. Thought it might be air in the line so I tried to bleed it.

Fluid level does change is I bleed with just the lever. I can now get the appropriate tension in the lever. Went for a quick test ride. In 5 mins of riding. The clutch lever lost tension once again and became spongy again.
 

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Discussion Starter · #4 ·
One added comment. The master cylinder bellows is warped and bloated no longer a v shape. Is that an indication of anything of note?
 

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The bellows can be wiped off of fluid and reshaped. No problem there.

The clutch can be a bugger to bleed. Some folks have had luck "flicking" the lever during the bleeding process...it'll release little bubbles. But be careful, flicking can also splash brake fluid on plastic and paint. You can also try to bleed at the banjo on the master. Some folks also tip the bike over (i think @Stick has had success using this method...he'll chime in).
 

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Discussion Starter · #6 ·
Thanks.

I will try the 'flick' and banjo bleed tomorrow. The slave cylinder is newer so I haven't been as focused there. The fluid is black/gray. So something is afoul somewhere. Seems like it is air or a faulty mc or both. I am just trying to narrow down the problem.

I will post an update tomorrow.
 

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Discussion Starter · #7 ·
Ok. So here is where I am now.

  • tried to reverse bleed with a syringe in the slave bleeder nipple (unsuccessful, did not seem to get the fluid all the way up in the mc reservoir
  • tried the 'flick' technique, uncertain if it helped
  • re-checked the slave, super clean, pushed with my fingers and a good spit of fluid in the mc occurred, travel seemed fine
  • did banjo bleed at the mc, felt good pressure in the lever after

5 min ride is all it took to begin to get spongy again.

I do hear some sounds from the mc when the lever is pulled and when I use a vacuum. And the fluid was black/gray. Seems like it should be the mc.

Anyone think I missed something? And what would you do: get a rebuilt kit or replace? Currently, I have a 13mm Brembo coffin style mc and matching brake mc.


Thanks for the input.
 

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The brake fluid in used in the clutch always goes dark pretty quickly...that's not the reason for your spongy issue. I still think you have a small amount of air in there. When you bleed the system, do you see bubbles in the fluid?
 

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Discussion Starter · #9 ·
When I bleed it via the slave bleed nipple it sometimes spits and sometimes pours or oozes. Might be related to how many lever pulls prior to cracking the slave valve. When I manually pushed the slave cylinder I did not see bubbles and when I bleed through the banjo bold, I could not really see it too well.

For some reason, I do not get good draw with the mity vac. Seems to work better with lever pumping and slave valve cracking with repetition.

I know air bubbles can be stubborn. Which of the techniques should I try a few more times?
 

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Discussion Starter · #11 ·
Unfortunately, there is not a bleed nipple inside the reservoir on this type of mc.

I did do a few different bleeds again today. I was running out of time and did a quick run and it seemed to hold pressure. I will get a more substantial ride in tomorrow to truly test it. I will post the result tomorrow.
 
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