Clutch Problems Help Required

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Blade
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Clutch Problems Help Required

Post by Blade »

After about 10 hours in the man cave over the last 2 days with little success I m in need of some help.

The plan was to fit a Sigma Slipper Clutch and Brembo RCS 16 Clutch M/C to my 2004 Honda SP2. With hindsight perhaps I should have fitted these separately and got each system working individually but being short of time I didn’t and decided to fit both at the same time.

Fitting of the slipper clutch went well. All friction plates were like new and within the tolerance of new plates so no point in replacing. I checked the metal clutch plates for warping and they were all perfectly flat. The only things I did decide to replace were the clutch springs as these were worn (but still within limits) so a set of 6 OEM Honda springs were sourced and fitted as a precaution. The fitting of the slipper clutch went well with no problems and all settings were within tolerance recommended and I even phoned Neil Spalding of Motogp fame to check my settings (He owns Sigma Performance) who confirmed all was good.

Next task was to fit the Brembo 16 RCS Clutch Master Cylinder and all went well with this or so I thought until I tested the completed set up and found the clutch is not disengaging correctly.

Basically with the bike up on the Abba stand and rear wheel in the air I put the bike in gear (engine off) pulled the clutch in and tried to turn the back wheel by hand. It was possible to turn the back wheel but only by exerting a reasonable amount of force so I think the clutch is not disengaging the plates enough and therefore dragging. For info I tried the same test on my Fireblade and the back wheel turns easily when in gear with the clutch pulled in. I put a DTI on the end of the clutch rod to see how much the pressure plate moves when the clutch lever is fully pulled in and found I have 0.7mm of travel which although I have no specific value I m trying to attain (figure unknown) this seems too small. (Note: I found some info on the internet that suggests the travel should be equal to one clutch plate’s thickness so in this case that would equal 2mm but I don’t know how good this info is)

I stripped the Sigma slipper clutch to check everything was put back together as per the manual and confirmed this was correct.

Next I thought I'll take the slave cylinder off and see how much the slave cylinder moves when the clutch lever is fully pulled in and I got the same value of 0.7mm. This proved to me that the problem is not with the Sigma slipper clutch as it is free to move and the amount of travel at the slave clyinder is equal to amount at the pressure plate so no travel is lost within the actual clutch unit if that makes sense. In my opinion its just that the slave cylinder is not moving enough (0.7 mm) to open up the clutch plates in the stack to disengage fully.

As the Brembo 16 RCS has a 16 mm piston and the OEM Honda master cylinder piston is 12.7 mm diameter I thought to myself is the Brembo RCS master cylinder not moving enough fluid to move the slave cylinder and subsequent clutch pressure plate by the correct amount. I don't think this is the case as A, Brembo recommend the 16mm RCS for my specific bike and B the Brembo RCS Master cylinder piston is larger than stock therefore if anything it will move more fluid so in theory the slave cylinder should move more or the same amount for less travel at the lever.

Therefore after trying all the above I m assuming the problem is air in the clutch line which means I m not displacing enough fluid out of the Clutch master cylinder to move the slave cylinder by the correct amount. I have checked for leaks and cannot find any. I have tried bleeding at the slave cylinder bleed nipple and the nipple on the Bremo RCS. I have tried injecting DOT 4 clutch fluid at the slave cylinder to reverse fill the system as well as the traditional method of filling at the reservoir by the clutch lever and bleeding the system down at the slave cylinder bleed nipple. I have removed the slave cylinder and tried pumping this by hand to displace the air to the high point at the Fluid reservoir. Trying all the above I have managed to move some air but as the travel is to little at 0.7 mm I think I still have some air in the system but bugger me if I can’t get it out. Note for info although the clutch lever is not spongy it does seem a little lighter than I would expect so this also helps confirm my theory of air in the system being the cause of the problem.

In short I have tried everything I can possibly think of with no success and therefore I m looking for some help from someone with more experience on the subject.

Do people agree its most likely air trapped in the system or could it be something I have over looked ?

Any comments or suggestions are most welcome. Thanks and hope some one can help.
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Re: Clutch Problems Help Required

Post by C00kiemonster »

I'd say it is likely air in the system. I'm no clutch expert, but I've had problems with air in brake lines before and had to fight to get it out.

Have you bled the rcs itself? If it's like the brake mc it has it's own bleed valves as well as the calipers (on the brakes). Short of that perhaps a mechanical bleed system that vacuums the fluid in/out.

Sometimes on clutches you have to preserve the engage / disengage levers position before work in the clutch itself? Is the system too engaged to start with so when you pull the clutch it works but can't pull it far enough?

You have my sympathies.. Sometimes it's better to walk away and approach it again after a couple of days! Good luck.
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Re: Clutch Problems Help Required

Post by C00kiemonster »

C00kiemonster wrote:I'd say it is likely air in the system. I'm no clutch expert, but I've had problems with air in brake lines before and had to fight to get it out.

Have you bled the rcs itself? If it's like the brake mc it has it's own bleed valves as well as the calipers (on the brakes). Short of that perhaps a mechanical bleed system that vacuums the fluid in/out.

Sometimes on clutches you have to preserve the engage / disengage levers position before work in the clutch itself? Is the system too engaged to start with so when you pull the clutch it works but can't pull it far enough?

You have my sympathies.. Sometimes it's better to walk away and approach it again after a couple of days! Good luck.
Oh.. Also. Is the fluid definitely dot4 or mineral fluid. Very different. Mine is a mineral fluid clutch as dot4 rots the seals and does have a different hydraulic basis. Just a thought....
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Re: Clutch Problems Help Required

Post by Blade »

Cheers for the comments Cookie.

Yes bled from RCS nipple. Yes its DOT 4. I have a bleed kit also. The clutch pach height is correct and the slipper clutch clearance is spot on. I have had problems bleeding other systems in the past but always managed to resolve it as have a range of tricks as described above but not worked this time.

Talking to someone else with an SP apparently the slave cylinder is a know problem and kicks off internally reducing travel. Oberon don't make a billet replacement unfortunately so will overhaul the stock item with new seals and try again.
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Re: Clutch Problems Help Required

Post by D6Nutz »

I can't add too much from a technical point of view, but from experience...

It does sound like it could be air, and I do agree with what cookie says. The RSV has to have a special type of fluid for the clutch, I can't remember off the top of my head what it is though (just not DOT 5.1). I also know that clutch systems when empty can be a royal arse to bleed.

I had the slave cylinder replaced on mine and I watched one of the guys from AP battle with to bleed the system for quite a while. He was trying eveything in book.

I hope you get it sorted mate.
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Re: Clutch Problems Help Required

Post by duke63 »

I don't know about the Honda system but i know that on the Ducati clutches the height of the clutch plates pack is critical to getting the clutch to engage and disengage properly.

Have you tried the bike on the road though?

Most bikes will drag the clutch a bit even with the clutch disengaged. Both my bikes need a little force to turn the wheel with the clutch disengaged. Try starting the bike on the stand put the bike in gear, disengage the clutch and put your foot on the rear tyre. You should be able to stop it turning.
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Re: Clutch Problems Help Required

Post by Blade »

Cheers Duke but already checked all that and bike won't go in gear with engine running as its not disengaging properly.

I'm going to rebuild the slave cylinder and replace the push rod.

Will call Neil Spalding for some advice too.
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Re: Clutch Problems Help Required

Post by Blade »

Starting to thing its not air now and could be push rod travel restricted due to weak slave cylinder.
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Re: Clutch Problems Help Required

Post by duke63 »

Read this, Blade?

http://www.rc51forums.com/forums/showthread.php?t=4006" onclick="window.open(this.href);return false;
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Re: Clutch Problems Help Required

Post by Blade »

Cheers Duke really appreciate the link but I had already seen it (traweled all Rc / sp forums for hours) and tbh doesn't tell me anything I hadn't tried already unfortunately. Its a very awkward one this one as I have tried virtually everything already.

Going to investigate more but very much think its a weak slave cylinder or very slim chance a sticking plunger rod. Both are easy to check so will do tomorrow as unfortunately busy today which is a shame as this is really bugging me and I just want to get fixed.
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Re: Clutch Problems Help Required

Post by Blade »

I m also hoping Neil Spalding will be able to tell me how much travel I should expect to disengage the clutch fully as I need a figure to aim for or could be chasing my tale trying to achieve more than is required.

At a kids play group now will call after lunch and hopefully have some more clues in which direction to proceed.

Thanks for peoples input.
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Re: Clutch Problems Help Required

Post by dizzyw »

Blade, might be useful might not, but when I was rebuilding my bro's fireblade we had a very similar problem with the clutch, we had to crack the banjo bolt to bleed it properly to allow the fluid actually into the cylinder, no matter what we did with bleed nipples, we just could not get fluid into it, once we did this all was well.
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Re: Clutch Problems Help Required

Post by Perkles »

I had problems bleeding mine on the Duc ,i taped the lever up over night and bled from the banjo bolt on the lever,i also had to fit a small spacer onto the slave pushrod which sorted it
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Re: Clutch Problems Help Required

Post by Blade »

Cheers Dizzy and Perkles but tried both suggestions with no improvement.

I thought about adding a spacer to push rod but won't this cause slip when running as partially disengaged ?
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Re: Clutch Problems Help Required

Post by Perkles »

Blade wrote:Cheers Dizzy and Perkles but tried both suggestions with no improvement.

I thought about adding a spacer to push rod but won't this cause slip when running as partially disengaged ?
it didnt cause mine to slip
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Re: Clutch Problems Help Required

Post by duke63 »

Oberon clutch slaves comes with a spacer for the clutch rod for certain Ducatis. But i would have thought if you needed a spacer it would have been included with the slipper clutch.
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Re: Clutch Problems Help Required

Post by Blade »

Oh that's interesting Duke cheers for the info.

Been in discussion with Oberon this morning but they don't offer a replacement for my bike which is strange as fits about 6 different honda s so plenty of potential customers.

After my discussions their design team may look into producing one but would be over winter so too late for me.

Tsr do a lovely one which is what hrc use and rumoured to be on the rcv bikes but at £210 plus import duty its expensive and I can't guarantee it will sort the problem.
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Re: Clutch Problems Help Required

Post by Blade »

Fitting a new oil seal might help as this is where the push rod locates so if its worn it could be part of the problrm
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Re: Clutch Problems Help Required

Post by Blade »

Really appreciate everyone's help. Thanks guys it good to get suggestions and sound out my ideas.

Will just have to continue working through one think at a time.
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Re: Clutch Problems Help Required

Post by Deegee »

I know you mentioned the new master cyl had a larger bore, but does it have sufficient stroke? I know Brembo recommended that unit, but countless times of having dealt with parts depts and their typos resulting in two nearly identical parts getting switched, I know it's not impossible. Anyway it's just a thought.

If you've got a DTI or a depth vernier it should be possible to double check the stroke and thus the displacement, same with the slave cyl. At least that way you'll know absolutely whether it's trapped air.
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