27 replies to this topic

[TOMMO0302]

The increased line bore is a good idea. To get your head around it, imagine trying to push (using the term lightly) 1 million litres of water down the River Severn, then the same amount of water down a stream....which is going to require more force?

[pogie]

Many thanks for your replies chaps and Tommo your analogy about the water and rivers is spot on and has finally got my head around line pressure.

Spud, I hope you don’t feel that I’m hi-jacking your thread, but it has really throw up some good ideas. In fact I’m so enthusiastic about getting back into the Mini, I’m going to pop run up to Mini Spares this afternoon and buy the clutch parts.

Edited by pogie, 13 March 2007 - 11:19 AM.

[TOMMO0302]

Good Stuff Pogie!

I'm sure you were planning on it anyway, but i would definately have a chat with them at minispares about your ideas and see what they think about the increased bore diameter...it may have adverse affects?

[spud]

Thanks for all the input everyone as there is lot's to think about.

Pogie, please let us know how you get on with your visit to minispares. Your thoughts on using a small bore master cylinder might (if it is possible to fit one) make a considerable difference. From what I can gather, the standard bore is 0.75 inches whereas the small bore version is 0.70. Now it might not sound very much smaller but by my calculations the area of the piston in the small bore version is approximately 10% smaller than the standard one. If my thinking is correct then does it follow that 10% less effort (force) is required to operate the clutch at the expense of 10% extra pedal travel to displace the same amount of brake fluid.

I'm sorry I'm not an engineer, and by all means shoot my theory down in flames, but your thoughts would be appreciated. Is a large bore hose available or would I have to get one made up? I take it that all the apertures, holes etc along the length of the hydraulic system would at least have to match the bore of the new hose? (ie master cylinder oulet and slave cylinder banjo holes)

Oh yes, anyone can hijack my threads I don't mind

Cheers,

Spud.

[pogie]

Thanks for all the input everyone as there is lot's to think about.

Pogie, please let us know how you get on with your visit to minispares. Your thoughts on using a small bore master cylinder might (if it is possible to fit one) make a considerable difference. From what I can gather, the standard bore is 0.75 inches whereas the small bore version is 0.70. Now it might not sound very much smaller but by my calculations the area of the piston in the small bore version is approximately 10% smaller than the standard one. If my thinking is correct then does it follow that 10% less effort (force) is required to operate the clutch at the expense of 10% extra pedal travel to displace the same amount of brake fluid.

Hi Spud. I asked the guys at Minispares about the bore sizes on the clutch master cylinders but they reconed there is only one size for all Mini clutches. I forget to ask about the old style brake master cylinders, so one of them could be used if they have a smaller diameter bore.

I'm sorry I'm not an engineer, and by all means shoot my theory down in flames, but your thoughts would be appreciated. Is a large bore hose available or would I have to get one made up? I take it that all the apertures, holes etc along the length of the hydraulic system would at least have to match the bore of the new hose? (ie master cylinder oulet and slave cylinder banjo holes)

I understand what you mean about the hose sizes and apertures along the system, I imagine the line pressure would be governed but the size of the smallest bore/aperture. It may be that you would have to open up the holes in the banjo bolts or the drillings in the slave cylinder to reduce the line pressure as far as possible. This would have to be done with great care as not to cause any leaks in the system.


My original idea was to strip and measure my own M/C and using the same calculations as you used, select an after market item. These are available in various sizes
http://www.demon-twe...CP2623-90PRM115
(though I would probably not buy it from D-Tweeks as the are normally very expensive when compared to other suppliers) and use it with a remote fluid reservoir. I saw a similar set up ages ago in one of the Mini mags on what I'm sure was a KAD built car of some description, so it looks like there should be an item somewhere out there to fit the bolt spacing on the Minis bulkhead.

I drove up to Mini Spares in Potters Bar and it's the first time I've been to them since they moved from Friern Barnet, it’s much easier to get to but I preferred the layout of the old shop. Anyway, I bought all the parts I need for replacing the clutch which came to around £160ish for everything from the flexible hose onward. Before I left home I checked to see if I could find my old flywheel puller, which of course I couldn’t, so I also had to invest in a new one and a 30mm socket to undo the bolt which is a different size to the one used with the old style flywheel.

Whilst the items were being brought out to me I preformed a very technical and rigorous test of the difference in line pressures between the standard flexi hose and a braided Goodrich item. Well that’s a bit of a fib, I actually just blew down each hose in turn and the one that took the least effort I deemed to have the lowest line pressure. The standard item won the test, so unfortunately no blingy braided hose for my clutch.

I explained to one of the guys behind the counter what I was thinking of doing and he (Gary?) agreed that what I had come up with would work. He also mentioned extending the pedal for better leverage, but it was his other suggestion that I really like. He said some racers who need to use high pressure clutches to deal with the power of their engines fit remote brake servos into the clutch line to reduce pedal pressure.

I must admit this was like a eureka moment, as it would take a allot of the guessing out of the equation and should also hopefully allow me to modify the engine and fit a performance clutch some time in the future . What's also good is that somewhere in my garage I have a remote servo from my old 1380 Clubbie that I used with a Cooper S disk setup. It will have been sitting in the garage for nearly 17 years so may be beyond repair, but if I'm lucky the conversion may only cost me the price of a servo rebuild kit, a bit of copper brake pipe, a tee piece for the brake servo vacuum line and some rubber hose. Gary said to tuck the servo under the dash in the passenger footwell where it would be out of the way, and then to plumb it in the same as you would for a brake set up.

Hopefully I will have the time this weekend to change the clutch, so I will see how the pedal feels after that and if it's still too heavy for me I will go down the route of fitting the servo.

I will add to this thread to let you know how I get on.

Cheers, pogie

Edited by pogie, 13 March 2007 - 10:07 PM.

[fikus01]

i was going to suggest fitting a single line cooper style servo but it looks like matey boy above me got there already, its totally possible,

[pogie]

i was going to suggest fitting a single line cooper style servo but it looks like matey boy above me got there already, its totally possible,

I can't believe I hadn't thought of it before. It was a proper "Doh!" moment when the Mini Spares guy suggested it.

[spud]

Well done that man!! Tis a good idea!!

Please keep us up to date with pics if possible if you plan on doing the job. In the meantime could you find any links to pics of the parts you are considering using as I am not familiar with remote servos. Am I right in thinking that the only connections required to the servo are the hydraulic pipe in (from clutch master cylinder), hydraulic pipe out (to clutch slave cylinder), and finally the hose connection which tees into the manifold to brake servo pipe?

Will the vacuum in the inlet manifold 'power' both servos when both pedals are depressed? To be honest I would rather do away with the brake servo if it came to it.

So many questions

Spud.

[spud]

I have now fitted , as suggested, a remote brake servo (secondhand) under the passenger side dash and piped it in correctly. I have used the 'copper' version of brake pipes and have tee'd the vacuum pipe into the exiting brake servo pipe on the brake servo side of the one way valve (or whatever it's called). I've done all that and it hasn't made the slightest bit of difference to the force required to operate the clutch pedal . When the engine is off the pedal is now stiffer than it was before and when it is running the pedal is as good as it was before the conversion.

The best modifications I have done so far are to move the drivers seat back until hit touches the rear bin and remove the steering column lowering bracket. This way, my left leg is in a straight line from my hip joint to the pedal. But I could still really do with the pedal being easier to depress!!

Could there be something wrong with the servo? How can I test it? The clutch flexi hose and the slave cylinder are in very good condition. Apparently it had been reconditioned/checked over before I bought it.I was under the impression that these servos are something like 2:1 pressure ratio, so ideally the force required should be half what it was. Surely the results should be better than this
Perhaps it is because I now have a brake and a clutch servo.

Any ideas anyone?

Spud.

[taffy1967]

Easiest way to test the brake servo, is to freewheel down a hill with your engine and ignition switched off and press the brake pedal firmly to gauge how it works.

Then repeat with the engine running and see if the pedal is softer?

[spud]

Should I assume that as the servo is in the clutch system and it is only marginally easier with the engine running that the servo is at fault?

Spud.

[taffy1967]

I guess you'd only know be trying a similarly equipped Mini and comparing?

But surely any improvement should mean it's working though?

[spud]

I've just taken it for a run and now realise that the clutch pedal is no easier with the engine running than without so I can only assume that the servo has a problem or something else is at fault. Are these servos difficult to strip down and rebuild?
Can anyone think of any reason why this system doesn't work?

Any help appreciated.
spud