Clutch lost pressure

The Other PaulG

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Hi all -

Any advice re a clutch that's lost its pressure?

The clutch system is from a 620 monster, it's a fairly traditional, simple hydraulic clutch set-up. Having bled both brakes without problem, I moved to the clutch. Plenty of fluid in the reservoir, I pumped the lever a couple of times (simultaneously opening the bleed valve whilst the lever's in motion, the way I have always done it).

After 2 pumps, the lever just went slack. No amount of faster pumps. slower pumps, tapping it along the hydraulic line etc helped. Still slack. I got out the vacuum tool and sucked form the slave cylinder end and the fluid really struggled to come through. The master cylinder was still almost to the brim at this point.

In any other circumstances I'd be thinking I need a master cylinder repair kit, but the bike has been ridden regularly and was showing no issues, and the first two lever pulls had the usual resistance.

So I'm a bit lost.

Any ideas?

Cheers!
 
Master cylinder seals just packed in? Either that or maybe some blockage between the reservoir and master cylinder - seems less feasible.
 
OK, a bit of an update.

Using the Mity-Vac, I can see that I am able to draw a lot of air out of the system through the bleed valve at the top of the slave cylinder, but even after many, many repeated attempts, I am still not getting any fluid to come out.

So.. that makes me think that there is air bleeding into the system around the nipple. (It's not bleeding in through a joint in the MityVac's pipes because with the nipple tight the system holds its vacuum).

It feels as if the nipple (11 on the diag) is not sealing well in its housing (10), so the vacuum is not drawing air and then fluid through from the hydraulic line and the cylinder, but rather constantly bleeding air past the nipple's thread. I tried a bit of plumber's tape on the thread - that didn't fix it, but the nipple feels a bit loose in its housing so I still think this is where the air's getting through.

Therefore, I think I need either a new nipple, or housing, or probably both as it's not clear which one's thread has worn.

That's my latest thinking - has anyone else had experience of nipples or housings wearing?

Cheers,

Paul
 

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Air leaking via the threads on the nipple will reduce the effectiveness of the Mity-vac but I can’t see that it’s the root of your of your problem.

I would fill the pipe with a syringe and some kind of improvised seal in the bleed nipple hole and then see if pulling the clutch lever gives you any pressure. I had a similar problem on my Sherco which turned out to be the master cylinder seals.
 
why don't you, just throw it away , and buy a Guzzi , like wot you said you were going to ..... you know it makes sense.






sent from Broadmoor Hospital.
 
take the slave off , and pump ...does it come out ? is it leaking ?

So... removed the slave cylinder and pump - just the same, no lever pressure.

Took the banjo off the slave and pumped - fluid does come through the hole in the banjo but only in very small amounts. Each pump yields a few drops - so little that the reduction of the level in the reservoir is barely perceptible even after 20 pumps. I did try cracking the banjo at the reservoir end, as suggested on the Monster forum, but whilst fluid did weep out, it didn't really bleed properly and didn't improve anything.

I have ordered new parts 1 and 11 at the slave end anyway because I think they're worn. But I think the answer has to be at the master end - either trapped air I can't release, or something wrong with the pump mechanism, maybe requiring a master overhaul kit.
 
Sounds like master cylinder seals passing- not shifting any fluid.
 
Sounds like master cylinder seals passing- not shifting any fluid.

And the winner is..... Deano, Baldrick, Chas and anyone else who suggested the master cylinder.

Just for the sake of the archive, Ducati say that a master repair kit is not available, and you need a whole new lever / clamp / cylinder unit at £140.

But.... the same master is used on some other bikes including various Guzzis. Guzzi do in fact offer the correct Brembo repair kit.

In the UK I ordered it from Gutsibits, under this reference:

BRA28659 Brake Master Cylinder PS13 Front Brembo Overhaul Kit

£26 incl VAT.

Fitted perfectly, I now have a properly clutchy clutch.

Thanks everyone for their inputs, much appreciated.

Paul
 


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