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Clutch Myth?


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#1 nospamprl

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Posted 15 August 2013 - 06:47 AM

I've been driving for nearly 40 years under the understanding that keeping the clutch pedal depressed is harmful for the clutch (like when in heavy traffic, I switch to neutral whenever I estimate the car will be stopped for more than 3-5 seconds).

 

Am I right or is it just an inherited behaviour? Sometimes it may be easier to just keep 1st engaged and the pedal depressed that switching from 1st to neutral back and forth.

 

Thanks.

 



#2 A-Cell

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Posted 15 August 2013 - 07:24 AM

For me too that is good practice. And on a mini you are'nt loading and prematurely wearing the crank thrust washers!
The safety brigade would also say that it an idiot hits you up the back you are less likely to have your foot slip off the clutch and your car shoot forward into the car in front, or worse the pedestrians walking across in front of you.

#3 mini_mad_andy

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Posted 15 August 2013 - 07:34 AM

Yep, I do the same. As A-Cell said it stops the wear on the thrust bearing, and also the clutch springs which is what tends to fail (become weak) and causes clutch slip.



#4 Old Bob

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Posted 15 August 2013 - 08:14 AM

No question that you are driving correctly - and I am sure your clutch lasts longer because of it.

 

Sometimes the old ways are best!

 

Bob



#5 jackmason

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Posted 15 August 2013 - 08:16 AM

I do the same!



#6 Guess-Works.com

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Posted 15 August 2013 - 09:18 AM

same should apply to automatics, when in stationary traffic, put the unit into neutral, instead of leaving it in drive... All you're doing leaving it in drive is over working the torque converter and the oil, degrading them both unnecessarily.

 

With manuals it's not so much the clutch which is wearing out, but the crank thrusts which has been mentioned above... changing a clutch plate is not really a big deal, but changing the crank thrusts is essentially a complete engine rebuild.



#7 JustSteve

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Posted 15 August 2013 - 09:18 AM

I also do the same. Don't do it if you ever have to re-take your driving test though! 

 

 

I find it an issue in slow moving traffic, with a 'mild' cam and a tall 1st gear. All the modern cars are able to creap at about walking speed while I'm having to slip the clutch.  :bah:



#8 Guess-Works.com

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Posted 15 August 2013 - 09:25 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.



#9 JustSteve

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Posted 15 August 2013 - 09:31 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.



#10 jagman.2003

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Posted 15 August 2013 - 10:39 AM

For me too that is good practice. And on a mini you are'nt loading and prematurely wearing the crank thrust washers!
The safety brigade would also say that it an idiot hits you up the back you are less likely to have your foot slip off the clutch and your car shoot forward into the car in front, or worse the pedestrians walking across in front of you.

 

That's my reasoning too. Also it's less wear on the release bearing. I also have a theory from many years of driving that the gearstick is linked to the traffic lights. As soon as I put it in neutral it will change to green..!



#11 Stiggytoo

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Posted 15 August 2013 - 11:05 AM

Just a quick question. When I pull away I tend to use very little revs and lift the clutch very early. The car will briefly judder. Is this better for the clutch/engine than using more revs and slipping it more?

#12 Ethel

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Posted 15 August 2013 - 11:21 AM

This could be a better place than hijacking Stevede's project thread....

 

The pre-verto clutch uses a diaphragm spring - like a shallow cone of steel that behaves similar to a frisbee of dustbin lid, in that the if you  push the centre in far enough it reaches a point where it's on the verge of inverting and popping out the other side. At  that point the spring won't be pushing in either direction, so won't be capable of putting any reaction force through the flywheel onto the crank thrusts.

 

I've mentioned this on Steve's thread, with a link to a good article on Minimania's site. Giving it some more thought, I reckon it's an idea worth developing. The Minimania article suggests setting up the clutch with the diaphragm spring flat when compressed: which would theoretically be that sweet spot. Would that work out in reality though? It's unlikely the stresses on either side of the spring would be exactly equal & opposite. What could be interesting would be to measure the actual effect on the pressure the spring transmits. I'd propose putting together a test rig to press on the clutch in place of the release bearing to measure the load applied:

 

Initially, to obtain the clamping pressure on the friction plate.

At the point the clutch releases, the minimum load you're likely to put on the thrust bearings.

The minimum value at, or near, the spring going flat, which would be our sweet spot.

 

We'd then tinker about adjusting the fitting height of the clutch diaphragm to try and get the sweet spot & clutch release to coincide so we can measure the effects and see what scope we have for getting the most holding power out of our clutches while minimising the wear on our crank thrust bearings.

 

Ideally, we could do with a hydraulic press with a pressure gauge that we can work out how much force is on our test rig - anyone?



#13 Guess-Works.com

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Posted 15 August 2013 - 12:05 PM

This could be a better place than hijacking Stevede's project thread....

 

The pre-verto clutch uses a diaphragm spring - like a shallow cone of steel that behaves similar to a frisbee of dustbin lid, in that the if you  push the centre in far enough it reaches a point where it's on the verge of inverting and popping out the other side. At  that point the spring won't be pushing in either direction, so won't be capable of putting any reaction force through the flywheel onto the crank thrusts.

 

I've mentioned this on Steve's thread, with a link to a good article on Minimania's site. Giving it some more thought, I reckon it's an idea worth developing. The Minimania article suggests setting up the clutch with the diaphragm spring flat when compressed: which would theoretically be that sweet spot. Would that work out in reality though? It's unlikely the stresses on either side of the spring would be exactly equal & opposite. What could be interesting would be to measure the actual effect on the pressure the spring transmits. I'd propose putting together a test rig to press on the clutch in place of the release bearing to measure the load applied:

 

Initially, to obtain the clamping pressure on the friction plate.

At the point the clutch releases, the minimum load you're likely to put on the thrust bearings.

The minimum value at, or near, the spring going flat, which would be our sweet spot.

 

We'd then tinker about adjusting the fitting height of the clutch diaphragm to try and get the sweet spot & clutch release to coincide so we can measure the effects and see what scope we have for getting the most holding power out of our clutches while minimising the wear on our crank thrust bearings.

 

Ideally, we could do with a hydraulic press with a pressure gauge that we can work out how much force is on our test rig - anyone?

 

 

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.

 

The two big nuts on the on the end of the plunger are there to stop this condition, the throw out stop nut. 

 

The spring must always have a return pressure or the plunger would not be pushed out where the clutch is released....



#14 Dan

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Posted 15 August 2013 - 12:19 PM

  If you manage to get it exactly flat, surely it will never re-engage the clutch as John says.



#15 Ethel

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Posted 15 August 2013 - 12:22 PM

I see that, it doesn't mean there isn't scope for fine tuning though. I'm thinking the diaphragm won't get that near flipping in reality, the stresses on it's faces aren't likely to equalise nicely as it goes flat. Performance diaphragms must also be a compromise as they are made to fit the dimensions of the, weaker, standard item. There should also be limited travel built into the pressure cover to flywheel clearance, which could be further tuned to make invertion impossible. The throw out stop is at least as much for stopping you directly pressing the fly against the crank thrusts when the cover butts against the fly.

 

You may be right that it's not worth the effort, but it would be interesting to see how much clamping force you can get with how little loading on the thrusts by optimising the diaphragm operation range.

 

I reckon the inertia of the pressure plate flattening the drive straps might also have a little effect on returning the clutch, but that's summet else entirely!






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