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Discussion Starter #1
Hey all,

I've had my Duc 748 for some time now. A friend of mine bought a Monster 900 last 2 Sunday's ago. I checked all the fluids for him, and changed the oil. I suggested he flush out the hydraulics as well but didn't get around to doing it.

So the other day he tells me he rode to work and the clutch stopped working. He opened up the reservoir cap and saw that it was pretty much empty. Told him to top off with Dot 4 and all was back to normal.

Next day I take my 748 to work, on the way back home my clutch started doing the same thing. Whenever I get on my bike in the morning I look at all the fluids, Oil, Clutch and brake fluids. I looked at my clutch tank at a stop light and noticed that it was really low and there was something black inside it.

Get home, open up the tank and fine the black rubber seal extruded towards the bottom of the tank as if it was getting sucked in. Tank was near empty, topped it off and back to normal.

What could cause (2) different Ducs located in (2) different places in the same town to loose all the Clutch fluid in the reservoir, yet maintain all the Brake fluid for front and rear brakes?

This is a mystery, only thing that comes to mind is the climate.

Any one seen this before?
 

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Check your slave cylinder for leakage.....:D
 

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Yep, almost surely leaky clutch slave.
 

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I'm guessing it's a pre-2001 748? Those have the crappy slaves that tend to blow seals easily. You'll probably open your sprocket cover and find mess of brake fluid in there.

For repair - cheapest is Evoluzione internals (a new aluminum piston with double seals that slots into the stock body). I have this, no complaints. Much better than simply changing the stock seal.

You could get a later post 2001 slave and fit a small spacer inside to make it work with an older bike. These are sealed units that are far less leak prone.

Blingy option is an aftermarket slave unit. Also the most expensive.
 

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Discussion Starter #7
Thanks for the replies,

its and after market slave installed before I took ownership. Haven't looked behind the sprocket cover since I changed the chain last year, but looks like I'll have to to see where all the fluid is going.
 

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Take off the sprocket cover & slave - the fluid is very good at running invisible down and under the engine... The standard seals are cheap enough but dont last long.
 

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Discussion Starter #9
Turns out y'all were right, didn't notice it before but there some fluid trickling down from the clutch slave.
Only problem now is I don't know if the oem o rings will fit my aftermarket clutch slave.

I can't identify the slave, it was on there when I purchased the bike years ago. Here is a pic, anyone seen one of these before?


Sent from my iPhone using MO Free
 

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I highly doubt that is stock.

I currently have a yoyodyne that is doing the same thing. After emailing back and forth for a little bit they explained they would replace it if it was a seal and not a spun bearing.

I can already tell them its not a spun bearing but have a feeling they will tell me its spun no matter what. And they never did tell me where to send it, and how to take care of the return as I would like to continue riding my motorcycle.

Maybe your company would be more helpful in the matter?
 

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Discussion Starter #11
Spoke too soon.

The clutch slave has a Pro Italia logo. I'm assuming that the o rings will work since the install on the pushrod etc

Anything I'm missing?

Thanks again


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Discussion Starter #12
So I finally took it apart last night. Turns out the oil seal was all cruded up but in tact. However, after a few phone calls I found out that the Slave was actually a custom built by a local dealer a long time ago. Rebuild kits are no longer available for it, therefore It makes sense to replace the 3 seals and the slave unit all together.

Now that I'm in the market for a clutch slave, I'm trying to figure out what bore size I should go with. I read different things about 28 and 30mm sizes.

Has anyone have experience with both sizes with Stock MC's? Is the 30mm worth getting over the 28mm? I like it to be easy, but I don't want to sacrifice in other areas over comfort.
 

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Old Wizard
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Partial clutch disengagement (clutch drag, elusive neutral) can be a problem with a 30 mm. The 28 mm slave is a better choice for 748s.
 

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Discussion Starter #14
Partial clutch disengagement (clutch drag, elusive neutral) can be a problem with a 30 mm. The 28 mm slave is a better choice for 748s.
thanks again Shazaam, I need to make my way down to your neighborhood one day and buy you a drink.

Cheers!
 
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