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Clutch Myth?


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#16 GraemeC

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Posted 15 August 2013 - 05:47 PM

I'm going to play devils advocate here.....

What do the throw out stop nuts on a pre-verto set up really do?
I think they're pretty pointless...........

#17 Guess-Works.com

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Posted 15 August 2013 - 06:45 PM

basically it stops you burying the clutch pedal into the floor pan... and running the risk of overthrowing the spring in the diaphragm.

 

For example, the throwout stop should be set so once the system is adjusted and bled, with someone pressing the clutch to the floor, the throwout stop should be wound in so it's against the face of the clutch cover, then with the clutch released, turned in again 1 flat and locked off.

 

This now means you clutch pedal does not hit the floor...

 

The same applies to a verto clutch.



#18 A-Cell

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Posted 15 August 2013 - 06:51 PM

Absolutely. This was the design intent of of the original mini clutch which was replicated when the diaphragm was introduced. Subsequently the Verto clutch was designed to fit within th same operating window.

#19 GraemeC

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Posted 15 August 2013 - 09:40 PM

And there's the point. You use the someones idea of maximum pedal throw, less 1 flat, to get the set point.

How do you establish that everyone holds the pedal down to the same point when winding up the nuts to the cover in the first place? What about carpet thickness, leg strength etc? It is not a measurable, repeatable procedure.
How do you KNOW this is enough to prevent overthrow? You don't, especially with lightened flywheels that could have the diaphragm at any point in its compression.
Is that one flat really going to make that much difference? Unless the diaphragm is right on the edge of overthrow then no, probably not.

Edited by GraemeC, 15 August 2013 - 09:41 PM.


#20 Ethel

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Posted 15 August 2013 - 10:21 PM

There's no point in pressing the pedal further than is needed to totally disengage the clutch, all that can do is push the flywheel & crank against the thrust bearing harder. The throw out stop ensures you can't.

 

I'll offer a slightly differing opinion to Guessworks & say the clutch cover will bottom out against the flywheel before the diaphragm can invert- if it didn't, relying on the throw-out stop wouldn't protect against the crank travelling towards the clutch and there'd be no  friction linings. Both types of clutch will just push harder than is needed against the thrust bearing, the pre- verto will be worse if all the give has been taken up  leaving you pushing directly on the flywheel.



#21 DILLIGAF

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Posted 15 August 2013 - 11:57 PM

Any spring will return to it's state at rest, when it's flat there is just less force trying to return it to it's natural position........

 

Verto clutches are set once when first fitted, the gap between the clutch cover and the through out nut should be set to 6.5mm...........

 

As I said before, if you set your clutch up properly (getting the spring flat) you will be amazed at the difference. Nearly as easy as a veto and thats with a orange diaphragm and fast road plate.

 

It's in Clive Tricky's Mini tuning books from decades ago........


Edited by DILLIGAF, 15 August 2013 - 11:57 PM.


#22 GraemeC

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Posted 16 August 2013 - 03:31 PM

There's no point in pressing the pedal further than is needed to totally disengage the clutch, all that can do is push the flywheel & crank against the thrust bearing harder. The throw out stop ensures you can't.

 

Now that makes sense - but in that case you would set the stop nuts by winding them in until the clutch didn't release, and then back them off a flat or two.

The standard wauy of setting them doens't take into account how far, or hard, the clutch release bearing is depressed - simply how far you can throw the pedal.



#23 Ethel

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Posted 17 August 2013 - 12:39 AM

Because the pedal throw is the usually the same limit: it will stop when the solid bit of the pressure plate, that carries the spring, hits the flywheel, and the attached crank hits the thrust bearing. Winding on the stop nut ensures you'll hit that rather than the thrusts when you press the pedal. You're right that you could possibly wind on the throw-out nut a bit more, and still have the clutch release, but you'd have to look at the pressure transferred to the crank via the pressure plate to decide if it was worthwhile. As I was waffling on about the design of the diaphragm spring is intended to reduce the pressure as it comes close to flattening out. The Verto is similar, it just has some of the leverage built into the spring itself. That's crafty because it puts the fulcrum on the crank assembly, so it doesn't "see" the same magnification of the leverage of the clutch release mechanism that the pre Verto does. you still need to make the same clearance for the friction pltare to slip (against similar clamping force). The lack of leverage evident in the Verto clutch arm is made up by the pressure  plate "fingers".



#24 jmmini

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Posted 17 August 2013 - 02:06 AM


 


Don't do it if you ever have to re-take your driving test though!

 
Why not ?
 
Handbrake on, gears to neutral, feet off pedals.
 
 
I read it as he swaps over before stopping  :shy: my mistake. 
 
But when I was learning to drive, my instructor told me that I should only ever put the car into neutral when I am parked up. I imagine this was his view though, rather than the examining boards.

My Instructor said the same also

#25 Dan

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Posted 17 August 2013 - 06:54 AM

  We must have all at some time or another sat and played with some kind of flat spring or small diaphragm from some machine or other, trying to force it to stay flat.  I know I have and as expected, when it is flat you can make it lock.  There is equal force trying to turn it each way and so it locks.  It is primed to go off either way and frankly would be quite dangerous if it were a powerful spring and not contained properly.  But they do lock up.



#26 Earwax

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Posted 17 August 2013 - 09:18 AM

For clarification please.  

 

Guessworks, when you said 

 

Unfortunately that is the wrong way to set up a diaphragm clutch... if the internal spring gets anywhere near flat then you run the risk of it over extending and then swapping sides, at which point you're stuck at the side of the road with no clutch.

 were you referring to the minimania article, Ethels idea or spring flat set up   ?  I was of a similar opinion to DILLIGAF ie flat adjusted

 

Any spring will return to it's state at rest, when it's flat there is just less force trying to return it to it's natural position........

 

Verto clutches are set once when first fitted, the gap between the clutch cover and the through out nut should be set to 6.5mm...........

 

As I said before, if you set your clutch up properly (getting the spring flat) you will be amazed at the difference. Nearly as easy as a veto and thats with a orange diaphragm and fast road plate.

 

It's in Clive Tricky's Mini tuning books from decades ago........

 

Not trying to start anything , just trying to learn from more experienced people   Cheers D



#27 DILLIGAF

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Posted 17 August 2013 - 09:36 AM

Well I've been machining the lugs on the back plate as per clive tricky's advice on every clutch I've run in my mini (ultralite flywheel & backplates)........



#28 Ethel

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Posted 17 August 2013 - 09:40 AM

I wouldn't want to speak for Guessworks, but he & Dan are making valid points.

To chuck in another analogy:

 

It's the same as pushing a car over a hump back bridge. You have to keep pushing just to stop it rolling back on you; as you get near the top it get's easier to push as the  "rate of climb" reduces; you could in theory get it to balance on the top of the hump; once it is at the top it can roll down either side. Substitute the car's gravity for the elastic force built up on both faces of our diaphragm spring. The ideal is to stop just before you reach the top of the hump so you can be sure the "clutch car" rolls back to where it came from. The top of our hump is where those forces equalise, which will be near, but not necessarily exactly, where the spring goes flat.



#29 DILLIGAF

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Posted 17 August 2013 - 12:10 PM

As usual on this forum people are rubbishing something they haven't tried, in direct contravention of what it says at the rules/guideines..........

 

All your actually doing by making sure the plates flat when engaged, is doing away with the manufacturing tolerances............

 

Thus making the clutch work as it was designed to...........



#30 Dan

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Posted 17 August 2013 - 09:19 PM

  Really?  It sounds like a discussion to me.

 

  In any case I do owe you an apology, last time you mentioned clutches I thought you were saying you could adjust the clutch to make it lighter, not install it to do so.

 

 I have an issue with what Clive Trickey has published about these clutches though, but I'm not certain either way because I haven't actually got all the performance data for the diaphragms used in the thing.  I did once have a big sheet from AP that compared them all and gave clamping loads and recommended HP bands for each, but I haven't seen the actual spring rate graphs for them.  Diaphragm springs can be manufactured to have more or less any characteristic you like, even a negative rate.  Certainly from the way it feels in operation the Mini clutch feels like the rate reduces dramatically toward the end of travel, and I guess that is the heart of this subject.  The thing is that if that trend is the same throughout the spring's range of movement, and I'm not saying that it is or isn't, then all you do by pre-loading it is lighten the clamping load.

 

 You say that a clutch installed to Trickey's recommendation (and I must say I haven't tried it) feels lighter in operation.  Well the thing is that the only way to make it feel lighter without increasing the mechanical advantage of the release system is to actually make it physically lighter.  I have never had a problem with keeping the clutch at the bite on an orange clutch, that's not what I was referring to before (an earlier thread).  I think the clutch is approaching flat at full pedal anyhow because as we all know the load drops right off, the problem is simply how tiring it is getting it there in the first place especially in traffic.  Now if installing one with some pre-load will lighten the pedal throughout the range that is great, but if all it's really doing is lightening the clutch pressure that's bad.  Why install an orange then de-rate it back down to brown by milling the bosses?  And the thing is that all the other tuners, and AP, and Rover, all say that the clutch should be installed at factory tolerance.  If this position is where the spring is designed to give its greatest effort then that makes sense.  If the clutch could be so dramatically improved just by taking more metal off of the pressure plate then why did the famously tight fisted BL spend all the money on the Verto clutch?

 

 I just don't buy that it's that easy to make that much of a difference with no penalty, and that nobody at the manufacturer went with that.  Remember that Clive Trickey died not so long after the diaphragm clutch was introduced to the Mini range (at least I think he did, I couldn't find a date when I looked but I think it was '69.  Apologies if that is wrong) and he would have been far more familiar with tuning the coil spring clutch.  Now pre-loading a coil clutch is a much better idea and may well increase the clamping load at the same time as raising the bite to a more convenient position.  But a diaphragm clutch is a very different animal and depending on how the diaphragm is designed is probably best being installed as the manufacturer suggests.

 

  These are my thoughts, it's called reasoned argument.  I'm not really expecting much in the way of a sensible response from Dilligaf to this but I post it in the hope it helps Earwax or anyone else.

 

  I'll readily admit I haven't tried installing a clutch in anything other than the factory setup, but this is my reasoning as to why it may be that all the mainstream advice is to just install it per factory.  If it feels lighter to do it the other way but clamps as tightly then fair enough, but if it feels lighter because it is lighter then personally I'd not bother.






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