New Sigma clutch slave cylinder

[Garth]

The one I took out does. That is how I identified the replacement I am getting. Elsewhere it had an FTE number so I have ordered an FTE one which is a third the cost !

[Ian Mackenzie]

When I did my Duratec conversion, I ended up machining the bell housing to get the correct clearances as I had non standard set up. When the clutch wears the finger will move outwards, so ideally you want around 1mm (2mm max) free in the slave before it hits the fingers at full compression. That was the measurements I went with.....

Stuart no doubt will be able to provide further advice.

Cheers

Ian

[John Vine]

...it would appear that even with the old CSC the pressure plate is preloaded by about 5mm by the CSC!

Do you mean that, when installed in the b/h and the whole caboodle hooked up to the engine, the bearing face of the CSC would be 5mm back from its rest position?  If so, I'd say that was entirely normal, as a degree of pre-load is needed to ensure the bearing face is in constant contact with the clutch diaphragm fingers.  (I don't know whether 5mm is the correct value, however, but it sounds about right.) 

ETA:  Thinking a little more about this, the CSC will need to be compressed a good deal more than 5mm.  RWD Motorsport have a natty little diagram here, suggesting that it should be compressed to within 3mm of its full travel.  The 3mm is to allow for clutch wear.

JV

[Garth]

Thanks Ian. I have spoken to Stuart and agree with your understanding of needing a few mm for the slave to be compressed further as the clutch wears. 

JV at the moment my CSC will depress the pressure plate fingers by about 5mm as when assembled the CSC will be fully compressed and then it will push the fingers in as you join the bell housing and block together as it has nowhere to go. I need to push the CSC back by 8 mm by machining down the bell housing support.  This will leave the CSC compressed to within 3 mm of full compression. It will then be pushing against the pressure plate fingers but not depressing/preloading them! Hope that all makes sense??!

Your link to the RWD Motorsports page was very helpful thanks

Garth

[Jim 123]

Maybe I am misinterpreting your description, but if the CSC is touching the pressure plate fingers in the rest position the CSC will be in constant ratation which will accelerate wear on the thrust bearing?

[John Vine]

Yes, that makes perfect sense, Garth, and I agree with your figures.  I misunderstood the relevance of the 5mm!

...if the CSC is touching the pressure plate fingers in the rest position the CSC will be in constant ratation which will accelerate wear on the thrust bearing?

Modern CRBs are designed to be in constant contact with the clutch diaphragm fingers.  If they weren't, they would have to accelerate up to crank speed in milliseconds every time you operated the clutch, which would lead to premature failure due to excessive heat build-up and loss of lubricant.

CSC bearings are kept in constant contact by the spring inside the bellows.  CRBs on cable-operated clutches are (or should be) kept in constant contact by a pre-load usually applied by a spring (or springs) operating on the clutch cable.  The long history of CRB failures in the cable-clutch K cars is pretty well all down to lack of this essential pre-load.  If you haven't already come across it, have a look at this article I wrote for LF on this very subject.

JV

[7 wonders of the world]

There are a number of different spacer thicknesses available for the Duratec CSC from Caterham.

[Garth]

Thanks 7 wonders but I need to gain space - not add to it!!

[Jim 123]

John re the link in #31, a very good article.

[Garth]

Hi JV

Have read your article with interest thanks. I am assuming that with the sort of clutch release bearing I am dealing with the preload is determined by the internal spring? It should follow then that with the bearing fitted in the correct position (with the correct clearances etc.)  one does not have to worry about the preload? Cheers. Garth

[John Vine]

Thanks for your kind words, Jim123 and Garth!

Yes, with a concentric slave cylinder (CSC) the pre-load is applied automatically by the (compressed) spring inside the bellows.

JV

[Garth]

The next trick will be to make sure it is not over extending as I understand if the clutch pedal stop is not set correctly the pressure plate can be pushed too far causing the clutch to start slipping? 

[John Vine]

You have a choice of location for the clutch pedal stop: footwell or pedal box.  Mine's mounted on the front footwell panel, but some have found the pedal box to offer a firmer and more secure mounting.

Either way, you need to set it (assuming you already have the recommended 3mm or so slack behind the CSC when it's compressed) so that you're able to de-clutch fully.  Then adjust the stop so that you have just a little more travel beyond that point. Discussion here.

JV

 

 

 

[Jim 123]

Garth my apologies if this is a stupid comment but I don't have the parts in my hand to play with.  Rather than machine the bell housing, is it feasible to shorten the pre load spring in the CSC? From your photo this may give the length of CSC assembly that you need. 

[Garth]

We have to machine the bell housing - evidently this is quite common.

There is no adjustment on the slave and in my case the slave would be fully compressed and then would also depress the clutch plate fingers by about 5mm as one tightened up the bell housing to the block!

I have to increase the distance from the front of my bell housing to the bearing face on the slave (see sketch attached earlier) from 76 mm to about 84 mm to ensure the slave is not fully compressed and has that 3 or so mm extra movement to allow for clutch wear. This means moving the slave back further into the bell housing and the only way to do that is to machine it down a little!

I think that is logical and makes sense??

[Jim 123]

I was wondering if you could take some coils out of the spring under the CSC gaitor to arrive at the same result rather than take metal off the bell housing. But as I said, I don't have any physical parts to hand to validate my thoughts, so my last post was just an idea before you start shaving metal off the casting. Looking at your photos I strongly suspect your CSC is a Valeo assembly and their tech people may have a stock part to fit your unmodified bell housing packaging and throw requirements.  The areas you plan to machine probably will have no impact of the casting integrity anyhow.

[John Vine]

I suppose one solution might be to use a bell-housing/engine spacer? Perhaps in conjunction with machining the CSC mount in the b/h? The snag is of course that the g/box rear mount would also have to be moved backwards.

JV

[Garth]

Hi Jim/John

I have tried to take my old slave apart - just to see how it works! It is not the springs that prevent the slave from compressing any further it is the physical shape of the parts. I have done a great deal of searching online to look for shorter slaves of this design and not come up with anything. There seem to be several OE manufacturers who do this part so I will drop one or two of them a line to see if they do a shorter version.

There is plenty of 'meat' on the slave cylinder support, so I am not worried about machining it down 8mm! I think this is a better solution than trying to move other components around thanks John!

I have a clutch stop in the bulkhead so will just use that.

[Garth]

Very Brief update..

Have a new slave it is an FTE part and identical to the Ford part it is replacing (turns out my original Ford one is made by FTE but costs 3 times as much to buy from Ford!). Bell housing being machined by Premier Power on Wednesday and then I can hopefully start putting it all back  together with the help of Alan and Graeme.

Fitting new master cylinder and hydraulic hose.

Thanks for all the help guys...

Garth

[Garth]

Final update - engine in again with correct position of slave in relation to pressure plate springs - new slave and master and it all works!

Still getting used to the new clutch action - uprated pressure plate - feels more like an on/off switch so a bit easier to stall pulling off!

Thanks for all the advice and also again to Alan and Graeme who helped me take the engine in and out twice!

Garth