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CNW Clutch slave.

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CNW Clutch slave.

Posted by gary_painter at September 08. 2018

I wonder if anyone happens to know what diameter bore CNW use in their hydraulic clutch slave?

I don't have one, nor intent to have one... Just doing a bit of maths on hydraulic systems for a bit of fun.

Elsewhere in the equation is the lift required for a Commando Clutch.

I've seen 0.1" (2.5mm) stated. Is there an optimum? What are folk getting on their Commandos?



Re: CNW Clutch slave.

Posted by nigel_keating at September 09. 2018

Gary, no idea about cnw slave and I don't know off hand what the lift is on mine  but I took some care to get the stack height correct with surflex plates and now it is lighter than any hydraulic clutch with no drag or slip. It does run dry though as I have a belt drive.

However this page may be helpful if you haven't already seen it.

Re: CNW Clutch slave.

Posted by john_holmes at September 09. 2018

961 question ?

Re: CNW Clutch slave.

Posted by gary_painter at September 10. 2018

Thanks for the replies guys.

Nigel, I don't have a problem setting up a cable clutch for light operation. I've been at it a few years now! The Ajay's and Matchboxes had the same clutch actuator in the AMC 'box, so on familiar ground.

I must admit that I didn't know there where different profiles available for the actuator arm, which I learned from the Atlantic Green article. Also where I got the 0.1" lift from... I had seen it, but thanks for flagging it up anyway.

Not a 961 question John. I'm just chewing over some thoughts about comparisons of mechanical advantage and clutch lift on cable and hydraulic systems.

Hydraulic doesn't always come out with the best Mech adv to lift ratio, but cables are notorious for drag and poor maintenance, so get bad press.

Still interested to find out what piston size the CNW slave has... Seems to be a well guarded secret!


Re: CNW Clutch slave.

Posted by gary_painter at September 16. 2018

So... Can anyone tell me the piston diameter of the Colorado Norton Works Clutch slave?

Or any other Norton Hydraulic conversion for that matter.

It's often debated how good Hydraulic systems are, compared to a well set up cable clutch.

I'm trying to compile a set of figures for mechanical advantage, clutch lift and cost, to compare the various set ups and post up as a sort of "What Clutch" article.

Any contributions welcome. 

Re: CNW Clutch slave.

Posted by katherine_scott at September 18. 2018

Previously gary_painter wrote:

So... Can anyone tell me the piston diameter of the Colorado Norton Works Clutch slave?

Or any other Norton Hydraulic conversion for that matter.

It's often debated how good Hydraulic systems are, compared to a well set up cable clutch.

I'm trying to compile a set of figures for mechanical advantage, clutch lift and cost, to compare the various set ups and post up as a sort of "What Clutch" article.

Any contributions welcome.


sorry I can’t help with the CNW information,  however happy to share what I used for my system, I machined my slave from aluminium bar an and my pistons in steel, orings work fine for test seals while you are experimenting  with slave bore diameter. After testing many combinations I finally went with 1" bore hard anodised my  slave used a seal kit from an Austin Healy 3,000 mk3. I also added a silicone oring to keep the gear oil off the seal. Master cylinder is 5/8 bore unit from FJR 1300 adjustable leaver with a decent stroke, works fine massive improvement on the original cable system.

If you search  my hydraulic clutch project their are some photo links.


Katherine Scott

Re: CNW Clutch slave.

Posted by gary_painter at September 22. 2018

Thanks for the info Katherine, and well done for having a go.

When you first posted a 7/8" slave piston I was surprised, as that would not produce a very good mechanical advantage, but you have edited that to 1" and it makes more sense.

I have gotten very bogged down with long calculations and measuring various leverage moments in the system. When suddenly I had an epiphany, you might say.

Of course mechanical advantage is only part of the equation. At the end of the day it's the overall mech adv from handlebar lever travel to clutch diaphragm lift that should be counted, and this doesn't vary significantly with whatever means are employed to transmit the handlebar lever force to the clutch, as it's more or less governed by the lever itself.

What varies is the effort needed at the lever to produce a given lift. It's fairly common knowledge that finding the sweet spot on the diaphragm via stack height is important to get the right feel to the lever, but that is the same for cable and hydraulic systems.

I have concluded that the advantage that hydraulic systems have over a cable is the lack of resistance and drag that the mechanical system can suffer and possibly the reduced maintenance.

I haven't counted the clutch cables that I have used over the years, but by and large they are no bother if lubed at least annually and routed sensibly. Every now and then though , one will be impossible to get sweet with routing or lubing, or at least will not stay sweet very long.

In recent years I have used one or two hydraulic clutches and have had no bother whatsoever except a weeping slave that I inherited from a previous owner and quickly fixed.

So I went round in a bit of a circle with the maths and came to a conclusion by looking at the question from a slightly different angle. I'm now happy to regard both systems as different, but not necessarily better or worse than each other..... Must get out more..! 

Re: CNW Clutch slave.

Posted by iain_brown at September 23. 2018

Hi Gary,

Jim Comstock makes the cNw kits, you could email him and see whether he will give the info. There will be contact details on his website

I have one on my 850, don't know the tech details sorry but functionally at least as good as any Commando cable clutch i have tried. Not everyone's cup of tea but nice to have the option.

I too would get out more - but i'm still working on my Norton.

Re: CNW Clutch slave.

Posted by gary_painter at September 23. 2018

Previously iain_brown wrote:

"I too would get out more - but i'm still working on my Norton."

Thanks for the info Iian, I will try Jim Comstock, But I imagine the piston size will be a fairly guarded trade secret!

Still working on my Commando too! I collected it a year ago in many boxes.

It had been in bits since 1979. So I have managed to loose assemble the grubby parts into something resembling a bike, just to see where everything goes and work out what upgrades to go for.

Obviously I'm listening to lots of Commando owners for advice, it being my first Norton after many Triumphs and AMC twins.

There seem to be two equally enthusiastic, separate camps, favouring cables or pipes. So I seem to have been embroiled in a little bit of over thinking with that particular issue!

About a year ago I went on a little ride out with a couple of mates on Triumph and Commando. we were all comparing clutch pull, my mates were in awe of my featherlite Ducati Monster's clutch (and the rattle!).

It just so happened that the Commando cable snapped during the ride. Although repaired with a spare in under 20 minutes, I decided there and then, that I would be fitting a hydraulic clutch to my Commando. Now it seems I have a foot in both camps?? 


Re: CNW Clutch slave.

Posted by neill_watkins at November 18. 2018


A bit of a late reply but I,m doing a hydraulic clutch setup over winter, using a BMW 32mm diameter slave cylinder and modified 5/8" Mk3 Commando master cylinder.

This is close to the ratio of the BMW setup: 32mm slave and 16mm Brembo master and the slave looks adaptable to the Mk 3 inner gearbox cover.

It,s a compact nicely engineered part with a sealed ball bearing thrust like a car and best of all, a single ball bearing that contacts the clutch rod, which will need shortening.

Looking at the Comstock slave cylinder photo, it must have a 30mm max piston and uses the Brembo 13mm master cylinder.

Long calculations not required, base your mod on existing setups, sometimes you can overthink these things.


Re: CNW Clutch slave.

Posted by gary_painter at November 18. 2018

Previously neill_watkins wrote:

A bit of a late reply.

Quite well timed as it happens Neill.

Yesterday I went to see how a prototype was getting on with an engineer chappie I met this Summer. We got chatting about the idea and the next thing you know, there is metal cut! I won't reveal his name just yet, but he knows Peter Williams and has worked on projects with him in the past... So no fool!

I decided on the Brembo 13mm master as used by CNW, I am familiar with the Brembo stuff from serial Ducati ownership anyway.

The prototype has a 28mm slave piston, which is the maximum that will fit in clutch actuator hole and be retained by the original threaded ring, whilst retaining a 3mm cylinder wall ( I doubt the CNW piston is much bigger unless the wall thickness is less)

Early results indicate an unbelievably light clutch pull,(estimated less than 10lbs) but insufficient lift.. Or probably just sufficient lift actually, but we are going to try a 26mm piston to try and get 2mm+ lift and hope the mech adv is not knocked too hard.

With a spring balance on my Ducati clutch lever I am getting 10lbs pull... That's light! When I tried this on the Commando with a jury rigged cable, looping out in one smooth arc (no twists and turns under the tank ect.). I measured a 22lb pull and to be honest that didn't feel extra heavy compared to other cable clutches I have fingered in the past.

Just pulling the cable in, to slightly deform the perfect arc, increased the effort at the lever considerably. I didn't "weigh" this but it does imply that the cable routing has a very large effect on the clutch pull. (like we didn't know that!)

This morning I was examining a slave made by the late Malcom Saggers, an old friend of mine whom you may remember from the Roadholder article on the AMC Unified Twin project... He built the first engine.

That uses a 31.75mm piston, but sadly we couldn't measure the master bore so the maths is big guess, but the action is smooth, light  and trouble free after many miles with Malcom and quite a few more in an Ajay with Colin.

Niell, your slave looks very nice and I like the bearing a lot. I will be very interested to see how you manage to mount it in the gearbox. Using the standard ring might be tricky as I suspect there is not room for it over the slave body (even with the lugs machined off). Perhaps you are thinking of tapping holes in the case to screw it on with the three lugs?

Also very interested to see how you have modified, presumably, a brake master? To fit the left handlebar? All I will say is, check the lift you can achieve with that particular ratio before you modify anything irreversibly... 2mm is desirable.

… To be continued..Wink

Re: CNW Clutch slave.

Posted by neill_watkins at November 19. 2018


plenty of interesting info there! I think we,re closing in on it in different ways. I vaguely recall Jim Comstock saying the clutch lift was around 0.100" to 0.125 so 2mm + may be OK. I had a chance to measure this when I replaced the pressure plate in August but forgot. Easy enough to check.

Malcolm Saggers piston is close to 32mm so may have used either 13 to 16mm master cylinder, the most common sizes.

Good guess re the BMW master cylinder mount, the 39mm o.d. body looks to be the right diameter to centre neatly into the threaded hole without the screw ring. I,ll make up a triangular alloy flange to match the slave, then bore and hand fit the centre diameter to fit over the over the existing alloy boss.

I,ll bond it in with epoxy and secure with three M4 or M5 grubscrews drilled in the line of the boss and flange to leave a flush face to meet the slave, then drill an tap the M6 mounting holes in the flange. Needs to be a solid permanent fit because it holds the shaft bearing in position if I,m not mistaken. The position of the flange still allows access to the nuts for the inner housing.

The Mk3 master cylinder is reversed with the reservoir removed and fitted to the other side with the small drillings redrilled to suit. Alot of cosmetic blending etc to match it to the brake side. The pivot point and lever are unaltered, basically like the Brembo but Norton Lockheed. Already modified an early type master cylinder like this for another bike, will send a pic later.

The complete setup can be checked for functionality off the bike and piston travel etc measured but don,t see any problems as it duplicates the BMW.. The exit point for the Aeroquip line from the gearbox will be the same as the cable. Broke a clutch cable en route to the Austria Rally in August, easily replaced in a leisurely 40 minutes, the only problem in 2800 miles, but my clutch has never been 100% easy. either with the original or my current lightweight Barnet assembly. I have a 13mm Brembo master cylinder just in case!

Katherine,s conversion is very good and I followed her progress on AccessNorton, but I don,t have access to a lathe and my usual local machinist has retired, so whatever fits and works the best with just hand fitting and blending will go on.

Re: CNW Clutch slave.

Posted by gary_painter at November 20. 2018

An interesting project Neill. I hope you can keep us up to date on here, as it develops.

I like the way you are solving problems with what resources you have and I love how you have reversed the Master. Ingenious.

It seems difficult to establish how much lift is required.. Especially without a running bike.

The Atlantic Green article states that the clutch is virtually disengaged at 1.27mm lift (Sorry to convert to mm but I find metric fractions of inches to be infuriating!) Also that the Commando actuating arm gives more than double the required lift, which I think I measured at about 3mm, but like yourself have forgotten!

I think I will be happy with a minimum of 2mm lift, anything more will be an insurance against dragging, but probably a waste of effort?.. We will see.

The master that Colin was using with the "Saggers" slave really did look and feel like a 13mm jobbie, but would have been producing very little lift at that ratio. However it was lifting the coil spring Ajay clutch perfectly, so maybe those don't need very much lift?

It's frustrating not having all the pieces of any particular jig-saw here, but the mist is clearing and do seem to have become hooked on the idea of having a hydraulic system on the Commando... Very keen to ride it but loving the build anyway.. Thank goodness I have a Ducati to ride in the meantime..

Re: CNW Clutch slave.

Posted by katherine_scott at November 21. 2018

Hi Neil

I will be keen to see how your project works out. I did test with a 14mm master cylinder, but clutch drag caused issues with finding neutral and harsh 1st gear selection. However both the bore and the stroke of the cylinder must be taken in to consideration.



Katherine Scott


Re: CNW Clutch slave.

Posted by gary_painter at November 21. 2018

Previously Katherine Scott wrote:

 However both the bore and the stroke of the cylinder must be taken in to consideration.


 Absolutely so Katherine. The master-slave ratio is not the whole equation.

The distance between the lever pivot and the piston rod is what governs the stroke of the piston. Longer master stroke = more lift.

How much you can move the lever with your hand, depends upon the size of your hands and how much adjustment, if any, there is in the span of the lever. However the clutch should still work properly with the minimum span adjusted in.

Fancy modern levers have lots of span adjustment..  Good for those with little hands.

Some of the latest radial lever sets also have adjustable stroke on the piston side of the pivot. This is done either with an eccentric pivot or by altering the angle of the piston rod to rest in differing positions on the lever

All very clever and perhaps a bit too much unless you really know what you're doing. Probably at least 60% gimmick in most cases! Besides which, a radial lever on a Commando would look a mite out of place!!

For the moment all that is adjustable on my project is the slave diameter, but it doesn't matter which element of the equation is manipulated. It's the overall ratio of lever movement to clutch lift that matters.

Re: CNW Clutch slave.

Posted by neill_watkins at November 22. 2018

Katherine Scott and Gary Painter

Good points raised and I will probably need to do some fine tuning with the pushrod length to suit the Commando clutch. BMW slave has around 8mm travel so final setting will be somewhere in between all going well, done at the diaphram end with everything bolted in place and light preload on the slave piston.

Mk3 master has the same pivot point as the 13mm Brembo, probably the 16mm too and I want to keep the lever span standard to match the brake side. There should be plenty of travel to play with, the standard Mk3 brake master handles my twin callipers with ease.

I,ll try 13mm and 16mm and select the best for ease and function, if 13mm is better I,ll sleeve to 13mm using the Madass140 kit, a well designed slide in mod rather than the drill and tap method used by others, currently $60+ shipping from the USA.

Look forward to getting it done, my clutch actuation has never been consistent at any setting, either with the completely standard setup or my lightweight Barnett, the cable that broke only lasted around 18,000 miles. Renewed my original Yamaha seals at 94,000 from new, no adjustment required ever, just occassional pivot lube and change fluid along with the brakes.

Re: CNW Clutch slave.

Posted by gary_painter at November 22. 2018

Neill, you will probably get away with the standard pushrod, as the adjuster is quite long. There's plenty of stroke available in your slave, but the biggest problem is going to be to get the piston "started" far enough up the bore to avoid bottoming on that circlip when the clutch is operated.

With a hydraulic slave, the adjuster is only used to position the piston in the bore with sufficient travel to work properly. once bled it stays in that parked position. The adjuster stays put, as no free play can be achieved, the piston always catches up with the rod and removes free play... Much as brake pistons move out to take up pad wear. (or rather, return less each time the brake is used.)

If we have the same handlebar lever moments, then I doubt that a 13mm master will move the 32mm slave very much. It moves my 28mm piston about 1.7mm or something.. 16mm should be much better.

With twin discs a 16mm master is ideal and a 13mm for a single disc, but don't be too quick to compare clutch operation with brakes. Brakes move very little, but use lots of pressure. High mechanical advantage is used to achieve high pressures on the pads.

The clutch only has to overcome the spring pressure but flow enough fluid to move the piston far enough to disengage the plates.

Loving this project...

Re: CNW Clutch slave.

Posted by neill_watkins at November 23. 2018

Gary Painter

Worthwhile project to be sure but all calcs, various configurations and combinations removed from

the equation now, got the nice bits I need to make it work, modification, assembly and installation next.

Won,t be till New Year now, got too much non motorcycle stuff to do till then and still enjoy riding the bike to work at the moment, snow and ice may put an end to that....

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