My clutch slave cylinder modification

After suffering clutch slave cylinder failure on my mid-2004 950 ADV at <20,000 km, I have been looking at ways to improve the poor design. I have purchased the uprated KTM replacement, but as it looks much the same, I don't have much faith in it.

Looking at the parts it became obvious that the plastic spacer had deformed, and by doing so, allowed the slave piston to skew in the cylinder.

I considered having a copy of the plastic spacer made in aluminium, but dismissed this as the design is quite complicated to make. I also thought of using the push-rod to hold the piston straight, but ruled this out as forces from the push-rod may subject the piston, and its seal, to additional stress. In the end I came up with the simple idea of inserting a brass bush into the plastic spacer so as to guide the piston. The brass bush was aligned accurately with the bore of the slave cylinder by using a specially made jig.

I have yet to fit the modified part, but will do so and report my findings.

Here is a photo of the inside of the spacer:

... and one of the outside:

I'm all ears ... (and eyes)
RC

The distortion of the spacer at least in my case, does not affect the shape of the hole, but the axle of the hole, in relation to the siting surface. The hole is no longer vertical to the surface where the spacer sits, due to distortion. The distortion occurs as a result of the forces applied by the piston on to the mounting bolts, being eccentrical to the center of the piston. At least according to my understanding.

Copying the spacer wouldn't have to be exact as long as the outer shape is similar and the inner circular homing reccess is exact. Cheers.

Hey Red,
it seems that you're on the right track trying to eliminate the distortion of the internal bore thus not allowing the piston to skew, what I don't think will work is the brass in the bushing. Wouldn't that expand much more than the aluminum and plastic creating more problems? With that said, I'm not aware of your internal O.D. of the bushing against the pushrod so it may not be an issue.
I'm curious to see how it's work.
Good luck
Alex

Guys,

Stop wasting time. The thing is junk fit only for the bin. So chuck it away and buy a Evoluzione instead. Fit and forget. More time for beer drinking then.

Agreed. There's already a superior fix out there. Spend your time on something more productive, like redesigning the water pump

How much time do you think I 'wasted'? The guy around the corner from my office modified the part in <1 hour and asked for £5 (US$10). I paid him £10 (US$20). Good for him. Good for me.

You say 'The thing is junk only for the bin', well, did you know that you have to use it with the Evoluzione unit?

I had already purchased a complete uprated slave cylinder from KTM (before the Evoluzione unit was available) as a result of what I'd read on OC. £85 (US$170). But I do not regret that, as my slave cylinder failed on holiday, and as the replacement unit was in my took kit, I was back on the road in no time! Thanks OC!

Also, an Evoluzione kit would cost me 235 US$ (180+56 postage)! That's a lot of beer where I live - 117 liters to be exact! No disrespect to Evoluzione, but that's a lot of money. And how proven is it? The basic design may have been tested well on other bikes, but not yet on the 950/990 ADV. We need to give it time to prove its self.

The Evoluzione cylinder does come with a 1 year warranty, but I would have to pay to post it BOTH ways - £56 (US$112) in the event of a claim. My first cylinder took 3 years to fail.

Some people (cpmodem, for example) have not suffered slave cylinder failure despite covering high mileage. Is it because he's a sympathetic (good) rider? Is it because he's good at preventative maintenance? Or is it that his machine has not been subject to high ambient temperatures - mine failed at around 40 deg. C.? I think it may be a combination of all three.

PS to Evoluzione: please don't take offense - if I had not bought a second KTM unit, and lived in the USA, I expect I would buy one of your units.

It's simply explained CP! It's because I have yet to suffer from water-pump failure. You don't see fixing the slave cylinder as a priority because yours has not failed. I don't see the water-pump as a priority because mine has not failed.

I am ready though - the parts are in my tool kit! Thanks to OC!

I also have one of these electric pumps on my bench ready for solving the water-pump problem... if I ever get around to it:

In my case the piston hole in the plastic spacer was oval - and not oval in the way that you would expect if the spacer was twisting as a result of the piston being off-centre compared to the mounting bolts. The hole was of a larger diameter towards the mounting points. It was quite bad.

I may have attempted to have a simpler version of the spacer made in aluminium, but as my bike is 3000 km away it would be too risky to make alterations to the original design without being able to check carefully.

What differences did you notice between the original spacer and the updated KTM unit? I think I remember you saying that the updated KTM unit is still working after two years' of use (how many miles/kms?).

Do you have a photo of the aluminium spacer that you had made?

It also struck me that our failed slave cylinders could be due to high ambient temperatures - mine failed in France in 40 deg. C after a long stint of hard riding, and you live in Greece... it can get hot down there, can't it?

Cheers!

It's a good point about the expansion. I think the aluminium of the piston will expand more than the brass bush. The geezer who did the job for me said that he thought brass was the best. The piston slides easily inside the bush, but there is some friction.

The diameter of the push-rod is a lot less than the ID of the bush. They will not even touch.


Maybe I should have had the bush made of aluminium so that it would expand at around the same rate as the piston. We'll see...

Sorry I meant the piston not the pushrod .
I keep on thinking that the main concern with these things is like you mentioned extreme temp riding and lack of maintenance. Also the fact that they collect all kinds of shit from the chain doesn't help either. I've been fucking around with better sealing the unit from the elements, I'll post pistures as soon as I come to a conclusion.
Cheers,
Alex

Oh, hand bags at the ready. Right here goes. I've covered 6000 miles since fitting the Evoluzione unit. It is still working perfectly and in that time I would have rebuilt the original crap at least 3 times. Funnily enough I was in the dealers today and a 05 was being dropped off a recovery truck because the slave was leaking and thats the new improved model. The dealer now keeps a large stock of seals because they keep failing. I would pay double the price of the Evo if I it gave me the piece of mind that I wasn't going to get stranded somewhere. Which I now have. Rant over. Resume normal service

When you say 'better sealing the unit from the elements' I take it you mean the joint between the plastic spacer and the engine, as the joint between the slave cylinder and the spacer has an o-ring. How about these thoughts:

1) Make a gasket from appropriate gasket paper.

2) Construct a curtain or deflector to shield the slave cylinder and the spacer from stuff thrown at them by the chain. Maybe a metal shield that fits between the engine and the plastic spacer, then bend it 90 degrees so that it forms a barrier between the slave cylinder and the chain.

Yes, but I think that the plastic spacer is the only part at fault - the piston needs it in order to function properly, but that does not mean that the piston or the cylinder are at fault. Everything else in the hydraulic clutch system should be able to cope with the heat. Easily. If a hydraulic front brake can survive under much higher temperatures, why can't the clutch hydraulic system?

Here is a list of the parts, and my opinion as to how they can be affected by heat:

1) Plastic spacer: Flimsy construction that distorts when hot and under pressure via the action if the clutch.

2) Slave cylinder casting: No problem from heat.

3) Slave piston: No problem from heat.

4) Slave piston o-ring: No problem from heat - often used in hotter places without difficulty. I say no problem, but

4) Hydraulic hose: No problem - same or similar stuff is used in the brake system, which gets hotter and is under higher pressure.

5) Clutch master cylinder: As a whole, no problem. I don't think it gets hot enough to cause concern, as it is so far away from the heat. Therefore I don't think it's rubber parts (plastic or metal as well) are suffering from heat. If anyone disagrees

6) Clutch fluid: I don't know what temperature the Motorex stuff can take because they don't say on their website. However, LHM Plus (Liquid Hydraulic Mineral) if perfect. It's easily able to withstand the pressure and temperature (>150 BAR / 2175 PSI, boiling point >200 deg. C). So if the Motorex stuff is failing due to excessive heat, just change it for LHM Plus. It's nice and thin so provides sensitive clutch action. But be careful - it looks good enough to drink!

Sorry to be so boring but enough people have had clutch problems to make it worth investigating properly.

Oops! Looks like you've got shares in Evoluzione

I am not criticising Evoluzione, but I am saying that their slave cylinder has yet to prove itself. 6000 miles is nothing. My, known to be bad, KTM unit worked perfectly for 12,000 miles - which is also nothing. So, lets see.

When my slave cylinder failed, the fluid was Black! I am quite sure that it was the original factory stuff; so clearly it was not up to the job. It was either eating something, or failing because it could not hack it.

Are you sure that your dealer is using suitable fluid? One of my dealers, who is a long-established off-road KTM dealer, said that he had not experienced many slave cylinder problems. The hydraulic clutches were used on the off-road bikes long before the LC8 road bikes appeared, so it's worth listening to what they have to say. The other dealer I don't trust, so shall not bother repeating the words, although they were not negative.

Even KTM Austria seem to be confused by this matter (check the Owner's Manual).

PS to union jack: please don't take any of this personally. Take it easy. I'm just looking at it objectively.

This is what I was thinking as well:
1) Making the gasket between the engine and spacer would be easy, yet not sure about the effectiveness, so being the lazy cunt that I am, I stuffed the underside of the spacer(against the engine) with high temp brake slider grease to see the results. So far after about 2,000 kms of mixed street and trail riding including mud, watercrossings and sand I puled the unit out again and checked it. Funny enough, there was a whole shitpile of dirt and sand and chain goo that was around the perimeter of the unit but nothing inside!! This seems to me like a viable solution, all I need to do is make the gasket now and try again.

2) As far as the deflector, I'm running the 17T front and I just can't how it'll fit in there, with no clearances. It seems that the Mattinhofen elfs like playing with very tight tolerances. I'll review the clearance again when I install my 16T

Cheers for now

I'm still on the same page here, I pulled my cylinder out first at 13,000km and the fluid had failed although there were no apparent clutch issues.
I'm currently running ATF(transmission fluid) which is about a 7W and although is a little sticky, hasn't given me any problems. The reason for this is that it has some swelling properties kinda like a seal renewer if you will.

What do you think about enlarging the mounting bolt holes like the EVO unit. That alone should stiffen the spacer.

By the way, I also think that EVO have done an excelent job in their unit, I just can't see me replacing mine until it gives me a reason.

Alex

I'm not sure what to think about enlarging the holes to help stiffen the spacer. The reason I'm questioning the value of this is that looking at my spacer it does not appear that the piston hole had been elongated by the twisting action caused by the piston being off centre. The piston hole is elongated up/down and not left/right (or front back, depending on how you look at it). I really think that the plastic spacer is too crap to use. It's just not good enough.

KTM say to use 10W fluid, so I expect a lighter fluid may quicken the response (good) but may leak more easily - although I think this is unlikely. The ATF should be OK with the heat. But I'm not sure what it'll do to the rubber (or plastic) inside the master cylinder.

What do you mean when you say that your fluid had failed - do you mean it leaked out or what?

It was just to the point of no return, no leaks just crappy looks and the viscosity of olive oil.

I don't think you need to enlarge the holes on the spacer since the factory bolts are loose on it. It would be a bit of an improvement since it'll hold the spacer tighter against the slave.