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Old Sep 2nd, 2007, 12:01 pm   #1 (permalink)
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Clutch Master Cylinder Adjustment




The master cylinder piston is adjusted at the factory so that, in its fully retracted state/starting position, the fluid return port to the reservoir is completely uncovered.

Essentially, until the piston moves far enough to cover the port, fluid can flow from the cylinder to the reservoir and thus the fluid is not pressurized sufficiently to cause the lever to generate the forces required for clutch release.

Properly adjusted, there should be a 5-10% dead-band of the full lever movement before there is pull resistance felt at the lever. This freeplay is necessary to prevent covering the port as the piston seal expands normally over time, and to avoid placing the piston seal rest location (where corrosion occurs) right at the return port orifice.

Once adjusted, the manufacturer places a potting compound over the screw adjuster to prevent accidental or incorrect adjustment.

If the potting compound is removed and the piston is incorrectly adjusted such that the return port is completely or partially blocked when the lever is released, the system will remain partially pressurized for a time, and the clutch engagement will be incomplete, causing slippage and premature wear. Similarly, the same mis-adjustment of the brake master cylinder leads to brake lock-up when the brake fluid heats up.

Itís been sugested here that you can do this adjustment yourself by checking for a squirt of fluid into the reservoir when you initially pull the lever, i.e. if you can see a squirt, itís OK. However, keep in mind that youíll still see a squirt with a partially blocked port. Clutch release problems are best solved by the proper selection of slave and master cylinder sizes. Reducing the amount of freeplay using this approach will allow you to move a little more fluid with the same amount of lever movement, but I donít recommend it.
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Old May 11th, 2009, 10:53 am   #2 (permalink)
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Adjustment for clutch master cylinder - 749

Quote:
Originally Posted by Shazaam View Post



The master cylinder piston is adjusted at the factory so that, in its fully retracted state/starting position, the fluid return port to the reservoir is completely uncovered.

Essentially, until the piston moves far enough to cover the port, fluid can flow from the cylinder to the reservoir and thus the fluid is not pressurized sufficiently to cause the lever to generate the forces required for clutch release.

Properly adjusted, there should be a 5-10% dead-band of the full lever movement before there is pull resistance felt at the lever. This freeplay is necessary to prevent covering the port as the piston seal expands normally over time, and to avoid placing the piston seal rest location (where corrosion occurs) right at the return port orifice.

Once adjusted, the manufacturer places a potting compound over the screw adjuster to prevent accidental or incorrect adjustment.

If the potting compound is removed and the piston is incorrectly adjusted such that the return port is completely or partially blocked when the lever is released, the system will remain partially pressurized for a time, and the clutch engagement will be incomplete, causing slippage and premature wear. Similarly, the same mis-adjustment of the brake master cylinder leads to brake lock-up when the brake fluid heats up.

Itís been sugested here that you can do this adjustment yourself by checking for a squirt of fluid into the reservoir when you initially pull the lever, i.e. if you can see a squirt, itís OK. However, keep in mind that youíll still see a squirt with a partially blocked port. Clutch release problems are best solved by the proper selection of slave and master cylinder sizes. Reducing the amount of freeplay using this approach will allow you to move a little more fluid with the same amount of lever movement, but I donít recommend it.

Hi Shazaam.. I am working w/ a 999 clutch master and running into the situation you mention - clutch slippage after repeated uses of clutch.

2 questions for you. .
1) How can I check if this return port is partially blocked? I don't see a partial quirt during initial lever travel. I've seen this on the brake side and know what to look for.
2) Where is this "screw adjuster" covered w/ potting compound?
(I've attached a pic of a master clutch cylinder similar to mine)

Thanks in advance for your help.
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Clutch Master Cylinder Adjustment-999clutchmaster.jpg  
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Old May 12th, 2009, 5:05 pm   #3 (permalink)
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You should see a squirt. The way is to change the stroke volume (of hydraulic fluid) produced by the clutch master cylinder by adjusting the screw (covered by a hot-melt glue in later years) located between the clutch lever and the handlebar grip. Increasing the stroke volume will increase the clutch pushrod stroke distance and consequently the clutch plate separation.

Here's what one looks like. Can't tell from your picture where it is on your unit.



You can increase the stroke volume by turning this screw IN about a half-turn. Mark its initial position for future reference. If you go too far, the master cylinder will not bleed back properly.

So, turn the adjustment screw OUT to move the clutch engagement point closer to the grip, and turn it IN to move it out. Remember to leave some play in the end of the lever after you're done, or you'll wear the clutch out prematurely.

A word of caution here. The reason that there is a factory seal over this adjustment screw is that it's not intended to be used as a service point for clutch adjustment. It's used by Brembo during final assembly to locate the clutch master cylinder piston in the proper position relative to a hole that allows the hydraulic fluid to return to the reservoir. Small changes here can make clutch function erratic and remove too much lever free-play.

It's possible to clean out a plugged port but a new unit may be in order. Also, make sure that the fluid doesn't have water in it down at the slave. Boiling water will cause slippage as well.
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Old May 31st, 2009, 11:42 pm   #4 (permalink)
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Clutch Master Cylinder Adjustment

Shazaam, Jackpot!!

It turns out that this port was easier to adjust that I'd imagined. The 999 clutch master has an adjustment screw directly in the plane of the piston travel. Anti-clockwise almost all the way. Then, started to see the little squirt back in the master cylinder.

This stopped "packing" the slave cylinder.

Thanks a ton for helping with this.
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Old Aug 11th, 2009, 9:19 am   #5 (permalink)
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Shazaam you're a genius! I spent so much time trying everything from clutch thickness, to new springs and all along it was just that adjustment. Thanks a million.
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Old Sep 23rd, 2009, 8:28 pm   #6 (permalink)
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Brilliant! If you want to check your work, remove the clutch springs and pump the clutch a couple time to jack the clutch pack open then put the springs back in. If the springs push the clutch pack closed you are good to go.

Thanks Shazamm
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Old Sep 30th, 2011, 12:09 am   #7 (permalink)
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Quote:
Originally Posted by Shazaam View Post


You should see a squirt. The way is to change the stroke volume (of hydraulic fluid) produced by the clutch master cylinder by adjusting the screw (covered by a hot-melt glue in later years) located between the clutch lever and the handlebar grip. Increasing the stroke volume will increase the clutch pushrod stroke distance and consequently the clutch plate separation.

Here's what one looks like. Can't tell from your picture where it is on your unit.



You can increase the stroke volume by turning this screw IN about a half-turn. Mark its initial position for future reference. If you go too far, the master cylinder will not bleed back properly.

So, turn the adjustment screw OUT to move the clutch engagement point closer to the grip, and turn it IN to move it out. Remember to leave some play in the end of the lever after you're done, or you'll wear the clutch out prematurely.

A word of caution here. The reason that there is a factory seal over this adjustment screw is that it's not intended to be used as a service point for clutch adjustment. It's used by Brembo during final assembly to locate the clutch master cylinder piston in the proper position relative to a hole that allows the hydraulic fluid to return to the reservoir. Small changes here can make clutch function erratic and remove too much lever free-play.

It's possible to clean out a plugged port but a new unit may be in order. Also, make sure that the fluid doesn't have water in it down at the slave. Boiling water will cause slippage as well.
Shazaam,

I think I made a big mistake. I've been trying to diagnose a nasty clutch slipping problem I've been having with my brand new clutch. When it get's hot, it becomes almost unrideable... slipping so much I have to stop for an hour or so to let it cool off.

It sounds like the screw on my master cylinder is misadjusted.. and so I played with it by screwing it all the way out (I hadn't read this article yet and thought it was dragging the clutch with it adjusted "in").

I'm not clear on the best way to figure out how to get it back to the correct location. Do I smoothly engage the clutch until I see movement in the fluid and then set it there.. or what?
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Old Sep 30th, 2011, 7:33 pm   #8 (permalink)
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Screw it in until you see no movement in the fluid, then back it off 1/2 turn at a time until you see movement in the fluid, worked for me?
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Old Jan 2nd, 2012, 11:02 pm   #9 (permalink)
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Thank you

OK so the Symptom I had:

- Bike is running fine when cold
- after 15-20 minutes seems like I have to ride the clutch

The worst this got was when I was in fist with the clutch out and the bike was not moving or stalling.

I tried to ride it and the engine was revving but bike wouldn't move.

Thanks so much for this thread as it saved me buying clutch plates and springs (which I thought required replacement).

Since I re-adjusted this the clutch has been sweet.

Try this first if you have the symptoms I mentioned as its a quick and inexpensive fix

Thanks again to the guy who wrote up the fix.... Legend..
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Old Mar 14th, 2012, 10:27 pm   #10 (permalink)
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thanks for this
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