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Discussion Starter #1 (Edited)
Seems that most people reporting clutch problems have a loss of pressure: i.e. pull in the clutch lever and no resistance/transmission won't disengage. My problem seems to be the opposite. When the bike ('96 900 ss/sp with 15k) is cold, the clutch engages pretty close to the handle (been like that since I got it). After about 30 mins of riding, the engagement point travels further and further away from the handle. By this time, when I release the clutch lever the engine whines as the transmission slooooooowly reengages with the engine. If I pull in the handle, I'm met with the same amount of resistance each time and shifting gears works just fine. If I let the bike sit for a day, everything resets itself and we begin the process all over again.

So, first time this happened I bled the clutch system. Problem persisted. Next day, bled again, this time REALLY checking for air bubbles. Problem persisted. This time I went after the obvious culprit and ordered a new slave, and just for good measure, put on a new pressure plate as well (read about bearings frying out, etc.). Push rod examination shows it to be straight, so relubed and put it all back together. Problem persisted :mad: Finally take it to the dealer. They cover the entire hydraulic system with foam to look for leaks. Find one at the master cylinder, so replace that and the put on a new hose as well (replaced everything from master to slave and in between by this point). Did a couple of short rides and it was fine. Let is sit for a few months waiting for summer to arrive in Seattle :sleep: Took it out this past weekend, and, once again, after 30 mins the problem returns :mad::mad::mad:.

Gonna go back to the dealer (have two to choose from, may pick the other one this time) when I can make the time to get it in. Just wanted some advice from anyone who may have experienced something similar, or has an inkling what the problem may be. Talk about frustrating...

Cheers,
HH
 

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Old Wizard
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3,006 Posts
Hydraulic clutches are self-adjusting so when the fluid expands from engine heat it sends the excess back to the reservoir in order to maintain a constant fluid volume. (When the fluid cools the reservoir returns the missing volume so the lever pull distance remains constant.) So, if for some reason the heated fluid can’t get back to the reservoir, the system gets pressurized and moves the pushrod causing slippage.



My guess is that the tiny master cylinder reservoir return port (on the left in the picture) is partially or fully plugged and the fluid can't return to the reservoir when the fluid heats up.

Another possibility is that someone adjusted it incorrectly and the return port is covered by the MC piston.

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.
 

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Discussion Starter #3
Thanks for the info! Given that the master is brand new, I would think we could eliminate it from the equation, but anything is possible :think:. Any other ideas?
 

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The master cylinder may be new, but did you use the same lever? I agree with Shazaams coments on whats causing the problem, and you may find it is the lever stopping the piston from returning fully. Do you have free play in the lever when hot?

It would be interesting to ride the bike until the problem occurs, then take the lever off and refit it straight away, and then see if the problem has gone for the moment. Just a test, not a fix, but it should prove if the piston is fully returning and uncovering the retrun port.

I wonder if the previous owner broke a lever and replaced it with the wrong one, or one with an adjusting screw set too far in?
 

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Discussion Starter #5
No, the lever is new as well. Still has the plastic in the head of the screw (that denotes it has not been changed from the factory setting... can post a pic if that doesn't make sense). Also, this new master doesn't have the external oil tank. It's a solid unit, so one less link in the system for a leak. New master, new braided cable, new slave, new pressure plate, same problem.

To answer your other question, yes, same amount of free play whether hot or cold.
 

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Old Wizard
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When the fluid gets hot, it expands and the engagement point moves away from the handle. When it cools down, the reduced volume of fluid causes the engagement point to move back toward the handle.

The feed from the reservoir is supposed to prevent this change of engagement point position by replenishing the volume of fluid lost when the fluid cools. It does this through the larger reservoir port (on the right in the above diagram.) In other words, the system is designed to be self-adjusting to accommodate temperature changes and clutch plate wear.

A plugged MC port can prevent refilling the master cylinder, but since it's been a problem for both master cylinders, my guess is that the reservoir or its feed line are partially plugged causing a restriction in flow back to the master cylinder.

I would first remove the reservoir and it's feed line and try to clear the flow with compressed air. It sounds like this is the only component that hasn't been considered or replaced.

Postscript

Another possibility is that someone has mistakenly mixed silicone-based DOT 5 hydraulic fluid with glycol-based DOT 3 or 4. Such a mixture will coagulate/gel causing fluid flow problems.
 

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Discussion Starter #7
Just wanted to follow up on this. We ended up bleeding the clutch master from top banjo bolt (the highest point in the system) and that did the trick. Just left over air bubbles from the previous work, building up and causing the engagement issue. Rode a couple hundred miles and all was well, until the electrical issue... :mad:
 
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