Discussion
If the clutch has got heavier after changing the slave and master cylinder then it doesn't have anything to do with the actual clutch itself. If the slave cylinder bore is smaller than the original then this will make it heavier; try and find one with the correct bore size or rebuild your old one if you still have it.
Aussie John said:
If the clutch has got heavier after changing the slave and master cylinder then it doesn't have anything to do with the actual clutch itself. If the slave cylinder bore is smaller than the original then this will make it heavier; try and find one with the correct bore size or rebuild your old one if you still have it.
Slave smaller bore piston will have more travel than the larger bore but pedal pressure will be higher 
Don't know how accurate this is or indeed if it will be of any help but I have just used a smooth piece of 3x2 down through the steering wheel onto the clutch peddle and some scales on top, it took around 35 lbs to "stroke" the clutch peddle through its travel. As stated on a previous thread I have bored my slave from 1" to 27mm some time back. Otherwise a standard 500 chimaera. I still wouldn't call it a lite clutch but I don't find it bothering me in traffic.
NZ fan said:
As stated on a previous thread I have bored my slave from 1" to 27mm some time back.
That's interesting, I'm wondering if you could take the ID out even further, perhaps to a size where a piston and seals from a larger slave would fit 
Still, I guess 1" to 27mm increase in diameter provides a significant increase in surface area...Sardonicus said:
yes: Slave smaller bore piston will have more travel than the larger bore but pedal pressure will be higher
Hydraulic ratios, hey
There's a formula for that
As we know the slave cylinder is operated by the master cylinder, so lets look at an example to establish the distance the slave moves.
-> A= 15,9 cm²
S(mm) = [V(cm³).10] / A (cm²)
Master cylinder oil flow per stroke of-> V = 3,5 cm³
-> S =( 3,5 .10) / 15,9 mm = 2,2 mm
So the slave cylinder moves 2,2 mm per pump full stroke actuation of the master cylinder.
This explains it well.
Essentially its just another form of gearing.
If your intimidated by the maths you can just cheat with one of them there online calculator jobies
http://www.engineeringtoolbox.com/hydraulic-force-...
But remember there's another set of gears at play folks, you need to throw in a leverage formula for your release arm to calculate the true movement at fingers on the clutch pressure plate.
It's easy to think that this leverage ratio will always remain a constant, but as Sardonicus quite rightly points out wear at the fingers will change it.
That wear may be only small, but you calculate it back through the length of the release arm & 1mm cam be 10mm of travel or more at the pedal.
I'd say the best option for a lighter clutch is to leave everything hydraulic just as it is, changing the hydraulic ratio is always going to change the pedal travel & where the clutch bite point resides along this travel.
Adding a small servo is going to help make the clutch feel a lot lighter at the pedal but the bite point will remain completely unaffected, something like the small clutch servos you used to see on a Mitsubishi 3000GT or Nissan Skyline should do the trick.
The problem (as always) with a TVR, is available space & packaging, everything is nearly always crammed in as tight as a Nun's chuff already.
For example, have a close look at the available space in the inner wing around the clutch mater cylinder, "feck all" I think best describes it
But if we could squeeze a servo in, I think the Nun would quite enjoy it
NZ fan said:
very good now please try and keep your mind on the job. Also less of the "down under" talk, I happen to believe that N.Z. is on the top of the world and I challenge you to prove me wrong.
sowwy.....it's watching the recording of the All Blacks playing Ireland this morning that got me started. Only got to half time - bound to go This thread has my total attention right now. Been on the phone to the USA re throw out bearings already, and I am now researching altering the clutch pedal fulcrum. I am loving TVR ownership, but my days may be numbered if I cannot lighten the clutch, thanks to the progressive arthritis in my left big toe and the consequent pain from operating the clutch.
QBee said:
sowwy.....it's watching the recording of the All Blacks playing Ireland this morning that got me started. Only got to half time - bound to go This thread has my total attention right now. Been on the phone to the USA re throw out bearings already, and I am now researching altering the clutch pedal fulcrum. I am loving TVR ownership, but my days may be numbered if I cannot lighten the clutch, thanks to the progressive arthritis in my left big toe and the consequent pain from operating the clutch.
Honestly, these guys are the experts.
I've seen cars with super light hand clutches before, if they can do that I doubt lightening a TVR clutch pedal would present much of a challenge.
http://www.youtube.com/watch?v=oiXnVl_KZ70#t=50
Worth a few calls, or why not chase up John Halstead, I bet he could come up with something.
Personally I dont think it would be just for those with arthritis, I believe we could all benefit from a lighter clutch
Calling Engineer1949
Edited by ChimpOnGas on Tuesday 26th November 17:26
Thanks Dave
Already in discussion with John by email, having met him and shared a garage at Snetterton earlier this month with him and Nick and the Orange Beast.
The mobility solution is a good possibility thanks, as is the idea of altering the leverage by moving the fulcrum of the clutch pedal.
Already in discussion with John by email, having met him and shared a garage at Snetterton earlier this month with him and Nick and the Orange Beast.
The mobility solution is a good possibility thanks, as is the idea of altering the leverage by moving the fulcrum of the clutch pedal.
QBee said:
Thanks Dave
Already in discussion with John by email, having met him and shared a garage at Snetterton earlier this month with him and Nick and the Orange Beast.
The mobility solution is a good possibility thanks, as is the idea of altering the leverage by moving the fulcrum of the clutch pedal.
Great, let us know what comes form your discussions with John.Already in discussion with John by email, having met him and shared a garage at Snetterton earlier this month with him and Nick and the Orange Beast.
The mobility solution is a good possibility thanks, as is the idea of altering the leverage by moving the fulcrum of the clutch pedal.
Just remember if you change the fulcrum point or alter the hydraulic ratio between the mater & slave cylinders you're going to change the bite point.
That might not sound like a big issue but actually you could very easily end up with something that's virtually un-drivable.
That's why in my opinion you're far better of avoiding the hydraulic or release arm mods altogether, and looking for some form of assistance.
The Land Rover crowd already do it with a servo, it's just they have a lot more space to work with.
http://www.briandorey.com/post/fitting-a-redbooste...
It's also worth having a look at how the aerospace industry tackles the the challenges of managing control systems in certain light aircraft.
Helper motors are an interesting solution, but I still think a clutch servo from an old Nissan Skyline or the like would be better.
Perhaps the answer the the space issue in a TVR is a reverse mounted master cylinder where the rod is pivoting above the pedal fulcrum point rather than below it as on the standard set up, so in effect your pushing down force is converted to act in the opposite direction compressing the reverse mounted master cylinder piston.
This would allow you to fit the master cylinder (and the moderately bulky Skyline servo mounted to it) up under the dash where there's significantly more space available than in the inner wing where the clutch master cylinder is currently mounted.
To help visualise my idea, here's a typical reverse mounted master cylinder arrangement (without a servo).
Now imagine it with a small clutch servo mounted to it.
All the bulk suddenly resides up under the dash, not crammed in the O/S inner wing.
Here's a complete assembly from a Mitsubishi 3000GT.
Well that's the way I'd tackle it
Edited by ChimpOnGas on Tuesday 26th November 18:32
NZ fan said:
Pink_Floyd said:
Chilliman said:
Still, I guess 1" to 27mm increase in diameter provides a significant increase in surface area...
20% extra.27mm (only 1.6mm bigger) = 572.5 square mm. 12.98% increase in surface area.
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