Need a nice strong clutch plate - this happened to my last 1

DEVONMAN · Post by **DEVONMAN** » Sun Jul 01, 2012 1:12 pm

Stevieturbo.
I was surprised by your earlier comment rergarding my statement that "clamping force increases as the pressure plate wears."

Wrongly or rightly I have believed this to be correct so following your comment I have consulted my books and they back my point of view.

It seems that when new the maximum clamping force is not achieved and this does increase as the plate wears and at a point well into the wear cycle clamping force then falls off rapidly but the plate is probably on the rivets by then.

Regards Denis

sidecar · Post by **sidecar** » Sun Jul 01, 2012 7:14 pm

Hi Guys,

Thanks for all the replies, I was wondering whether the pressure plate has an ideal size for the drive plate, a bit of a guess but I reckon that the borg and beck plate was probably 8mm thick when it was new.

I'll let you know what Helix say but I bet they will just say I should have purchased the pressure plate that they recommended. The problem is that does not explain why one drive plate is OK with my current pressure plate but another one is useless. (Unless the 0.2mm is taking the diaphragm over its maximum, if this is the case then it all seems a bit too marginal to me)

cheers,

Pete

stevieturbo · Post by **stevieturbo** » Sun Jul 01, 2012 7:49 pm

DEVONMAN wrote:Stevieturbo.
I was surprised by your earlier comment rergarding my statement that "clamping force increases as the pressure plate wears."

Wrongly or rightly I have believed this to be correct so following your comment I have consulted my books and they back my point of view.

It seems that when new the maximum clamping force is not achieved and this does increase as the plate wears and at a point well into the wear cycle clamping force then falls off rapidly but the plate is probably on the rivets by then.

Regards Denis

Do the books explain how this is achieved ?

I had issue with a clutch just a few months ago, and I tested several pressure plates and their clamping characteristics in a press testing clamping pressure every 0.2mm

Your explanation would totally contradict everything I tested. And the friction plates when brand new didnt come close to ever achieving maximum clamping pressure that was possible. Obviously this is simply down to manufacturing tolerances, and them wishing never to go beyond the covers normal position, ie over centre as if your foot was on the clutch

The only strange thing I encountered, was the clutch cover with some 130k on it had a much higher clamping pressure everywhere than the brand new ones I was comparing to. Right from the force it took it to move at all.

DEVONMAN · Post by **DEVONMAN** » Sun Jul 01, 2012 9:30 pm

stevieturbo wrote:
DEVONMAN wrote:Stevieturbo.
I was surprised by your earlier comment rergarding my statement that "clamping force increases as the pressure plate wears."

Wrongly or rightly I have believed this to be correct so following your comment I have consulted my books and they back my point of view.

It seems that when new the maximum clamping force is not achieved and this does increase as the plate wears and at a point well into the wear cycle clamping force then falls off rapidly but the plate is probably on the rivets by then.

Regards Denis
Do the books explain how this is achieved ?

I had issue with a clutch just a few months ago, and I tested several pressure plates and their clamping characteristics in a press testing clamping pressure every 0.2mm

Your explanation would totally contradict everything I tested. And the friction plates when brand new didnt come close to ever achieving maximum clamping pressure that was possible. Obviously this is simply down to manufacturing tolerances, and them wishing never to go beyond the covers normal position, ie over centre as if your foot was on the clutch

The only strange thing I encountered, was the clutch cover with some 130k on it had a much higher clamping pressure everywhere than the brand new ones I was comparing to. Right from the force it took it to move at all.

One book shows a graph which indicates clamping force against wear and this shows increased clamping force as the clutch wears. My own understanding is that up to the point where the diaphragn goes flat and then overcentre, the force reduces towards zero. So conversely, the force increases when the diaphragm moves towards the released position. Thats why the pedal force get less when the clutch pedal is on the floor.

I can imagine that in a racing car situation it would be desirable and possible to set the clamping force at the maximum when new but for a road car the makers would need to ensure a non slip situation for high mileage/constant traffic use and a gradual reduction of the designed initial clamping force would not be acceptable as it would deminish the effective life of the clutch as it used to with the old spring type Borg & Beck clutches.

In your penultimate and final sentence above your statements totally agrees with my initial point that the clamping force increases as the clutch wears, so we seem to be going around in circles on this one.

Regards Denis

stevieturbo · Post by **stevieturbo** » Sun Jul 01, 2012 10:34 pm

DEVONMAN wrote: My own understanding is that up to the point where the diaphragn goes flat and then overcentre, the force reduces towards zero.

Again, this is not what Ive seen through actual testing.

The thicker the friction disc gets for wont of a better way to describe it. Pressure increases ( almost linearly actually ) up until the point where it is going causing the diaphragm to go over centre
Clamping force does ease off slightly there and once over centre drops again.

It's behaviour is quite normal and expected in my opinion. It is just a spring after all, it cant really behave any differently.

To suggest it could clamp more with reduced spring pressure, as would happen as the friction disc gets thinner just makes no sense whatsoever

I certainly cant think of any circumstances any spring would behave like that during it's normal travel ( ie not a coil bound or something )

DEVONMAN · Post by **DEVONMAN** » Mon Jul 02, 2012 7:48 am

stevieturbo wrote:
DEVONMAN wrote: My own understanding is that up to the point where the diaphragn goes flat and then overcentre, the force reduces towards zero.
Again, this is not what Ive seen through actual testing.

The thicker the friction disc gets for wont of a better way to describe it. Pressure increases ( almost linearly actually ) up until the point where it is going causing the diaphragm to go over centre
Clamping force does ease off slightly there and once over centre drops again.

It's behaviour is quite normal and expected in my opinion. It is just a spring after all, it cant really behave any differently.

To suggest it could clamp more with reduced spring pressure, as would happen as the friction disc gets thinner just makes no sense whatsoever

I certainly cant think of any circumstances any spring would behave like that during it's normal travel ( ie not a coil bound or something )

I think you are wrong to compare a diphragm to a normal coil spring.
The diaphragm does not act in a linear manner and forces follow a sine wave form.
As the diaphragm approaches the flat shape the forces tend to zero.
A well designed clutch will stay within this approach zone for a plate at both new and worn thickness.
If the force tends to zero in one direction then it follows that it must increase in the opposite direction but only within this zone. (the wear zone).
Outside this zone the forces go over the crest of the sine wave and diminish rapidly.

Regards Denis
As it approac

stevieturbo · Post by **stevieturbo** » Mon Jul 02, 2012 9:36 am

Again, that is not how real world testing shown it's behaviour.

Clamping pressure did fall from a maximum of around 1500psi once it did go over centre, but it certainly never went anywhere near zero and it would be impossible for it to do so.

Sure you arent mixing up foot travel pressing on the centre of the diaphragm compared to me talking about actual disc clamping forces ?

Foot effort required may reduce slightly once over centre, but even that wouldnt drop to zero ( as anyone knows it still takes effort to hold the pedal down )

DEVONMAN · Post by **DEVONMAN** » Mon Jul 02, 2012 2:49 pm

stevieturbo wrote:Again, that is not how real world testing shown it's behaviour.

Clamping pressure did fall from a maximum of around 1500psi once it did go over centre, but it certainly never went anywhere near zero and it would be impossible for it to do so.

Sure you arent mixing up foot travel pressing on the centre of the diaphragm compared to me talking about actual disc clamping forces ?

Foot effort required may reduce slightly once over centre, but even that wouldnt drop to zero ( as anyone knows it still takes effort to hold the pedal down )

Again, we are getting nowhere with this discussion.
I used the term "tend" to zero as I agree it is unlikely to reach actual zero.
If you PM your email address I will gladly send you the diagram from the Clutch and Flywheel handbook I have.
(Don't think I can put it on here ,copyright etc)

Or maybe someone else on here is willing to comment.

Apologies to the original OP as this discussion is no doubt not helping you.

Regards Denis

sidecar · Post by **sidecar** » Mon Jul 02, 2012 4:15 pm

I think the OP has long gone! I then hijacked the thread.

Anyway I spoke to Helix today who told me to speak to Mardi Gras in Silverstone as that's who I actually bought the drive plate off.

Not surprisingly they reckon that I need the matching pressure plate, the chap reckons that pressure plates are designed to work with certain thickness of drive plate. I then told him that the new plate was 8mm and the old one is only 0.2mm thinner. He more or less agreed that it was unlikely to be the cause of the problem but could not offer any more advice other than to buy a new pressure plate.

I'm now at a bit of a loss, I have a load of part numbers off my pressure plate and it has red paint on it so I'll spend some time trying to find out some info on it off the web.

Cheers,

Pete

DEVONMAN · Post by **DEVONMAN** » Tue Jul 03, 2012 8:04 am

sidecar wrote:I think the OP has long gone! I then hijacked the thread.

Anyway I spoke to Helix today who told me to speak to Mardi Gras in Silverstone as that's who I actually bought the drive plate off.

Not surprisingly they reckon that I need the matching pressure plate, the chap reckons that pressure plates are designed to work with certain thickness of drive plate. I then told him that the new plate was 8mm and the old one is only 0.2mm thinner. He more or less agreed that it was unlikely to be the cause of the problem but could not offer any more advice other than to buy a new pressure plate.

I'm now at a bit of a loss, I have a load of part numbers off my pressure plate and it has red paint on it so I'll spend some time trying to find out some info on it off the web.

Cheers,

Pete

Hi Pete,
Given you say you are at a bit of a loss, just a few possibilities why the new plate (just 0.2mm thicker)is slipping.

1. If your flywheel and pressure have seen heavy use or high milage, the surfaces may no longer be true and parallel. Your old plate may have worn to suit this situation and therefore is making full contact.
In the case of the new plate, due to flywheel wear etc it may be clamped more towards the centre and therefore would effectively be acting as a smaller clutch.
This should improve with wear in.

2. The new plate has less grippy material.

3. Your clutch is only just adequate for all those horses/torque you have and given the wear mentioned in 1 above, the new plate may become just adequate and not slip when it wears in to current flywheel profile.

Just my humble thoughts.

Regards Denis

JP. · Post by **JP.** » Sat Jul 07, 2012 7:01 am

When I bought my McLeod Street/strip clutch kit from Real Steel, Charles told me to break in the new plate for a few hundred miles and not fully load it. Like breaking in new brake pads.
Charles warned me not to (drag) race the clutch kit directly out of the box.

Charles also told me the drivenplate only does about 25% of the clamping, while about 75% of the clamping force is generated by the pressureplate and offcourse a good faced flywheel.

I wonder if Helix told you to break in the clutchsystem you bought or where you alowed to fully load the kit straight out of the box.

Just some personal information I wanted to share in this topic.

sidecar · Post by **sidecar** » Sat Jul 07, 2012 9:29 am

JP. wrote:When I bought my McLeod Street/strip clutch kit from Real Steel, Charles told me to break in the new plate for a few hundred miles and not fully load it. Like breaking in new brake pads.
Charles warned me not to (drag) race the clutch kit directly out of the box.

Charles also told me the drivenplate only does about 25% of the clamping, while about 75% of the clamping force is generated by the pressureplate and offcourse a good faced flywheel.

I wonder if Helix told you to break in the clutchsystem you bought or where you alowed to fully load the kit straight out of the box.

Just some personal information I wanted to share in this topic.

Hi JP,

Helix did not tell me to break the clutch plate in but I did think that it might be required. I did load it up as soon as the engine was warmed up and it slipped once the revs got above 4k. I did not let it slip for more than a second or two because I did not want to over heat anything. I tested to clutch a couple of times and it consistently slipped for a second or two. Not sure what you mean by 25% of the clamping is done by the drive plate, I would have thought that all of the clamping is done by the pressure plate.

The flywheel and pressure plate both have good, well machined surfaces.

My new close ratio (tall first gear) gearbox has just arrived so I'll be pulling the transmission out shortly, I'll have a good look at everything then. I'm thinking of fitting a 'Green spring' AP pressure plate with the Helix drive plate, they are good for 340 ftlbs of torque.

The company that I actually bought the Helix plate from is called Mardi Gras, they have offered to test my pressure plate on their test rig. I've searched to web for hours but cannot find any info on the pressure plate, it has a red spring. (I can find pictures of it but nothing else). RPI have given me the part numbers but that has not helped. I 'suspect' that it is rated at 270 ftlbs.

Cheers,

Pete