Manual transmission Clutch Question...

[poomanchu]

Originally Posted by sarguy01

First off, the clutch cannot LOCK in a 1:1. So his statement was not “spot on”. In the world of friction, there can always be a chance of slip. Two metal plates with a disk sandwiched in between is hardly an absolute locking device. If there were some teeth, gears, etc that locked it, fine. But there aren't any mechanical engagements on the Civic clutch. It works on the principles of friction. A clamp relies on friction as well. Have you ever had a part, that was clamped tight, move? I have and it's because the force acting on that part overcame the friction holding it in place.

Again, I am not suggesting the clutch is slipping at all times. I am suggesting an engaged clutch can slip under certain circumstances. I am not saying it WILL, I am saying it CAN. I do not think that while I am driving my clutch is constantly slipping.

There is a lot of clamping pressure. But, that is not directly correlated to the amount of torque a clutch can hold under given circumstances. One ton of clamping pressure doesn't mean the clutch can hold one ton of the engine’s torque. There are a lot more factors, like the constantly changing coefficient of friction, as sited in one of the articles in the original post. Also cited in those articles, were the explanations about the differences between dynamic and static friction, outside factors, etc. It was actually some interesting reading.

In our world, we can assume all we want about the clutch not slipping. But, under the physics world, a clutch can slip. Do you disagree??

I have stated what I said., Yes, the clutch does LOCK in a 1:1, if it is not locked, it is slipping. If it is slipping while engaged, it or whatever is causing it to not clamp with full pressure needs replaced. Though the disk is probably fried by then.

Can the clutch slip in normal operation? yes, by manipulating the clutch pedal you manipulate the clamping pressure which LOCKS it into place. So there is some slip transitioning from engaged to not engaged. But besides that there should be no slip.

Don;t really know what else to say. The person who I quoted as spot on is still..spot on. An engaged clutch does not slip. Yes it is not mechanically welded or bolted together (would defeat the point of a clutch), but it does lock into a 1:1 through the force exerted by the pressure plate and friction material of the clutch.

Can an engaged clutch slip under certain conditions? Yes, like if it is failing or overheating or there is a material between the flywheel and clutch causing slippage.

[sarguy01]

Originally Posted by wdb

But that's how I read your post - that a clutch is never fully engaged and that some slippage was always occurring.
CAN slip, sure. DOES 'slip', a tiny bit, i.e. the flywheel and pressure plate do not maintain perfect 1:1 rotation, under certain circumstances, when the operator would otherwise assume that it was not slipping, sure. But *always* slipping? I don't buy it.

I did say always. I did however correct myself and have since changed it to "under certain circumstances".

I sometimes type quicker than I think. Sorry for the confusion...

[sarguy01]

Originally Posted by poomanchu

I have stated what I said., Yes, the clutch does LOCK in a 1:1, if it is not locked, it is slipping. If it is slipping while engaged, it or whatever is causing it to not clamp with full pressure needs replaced. Though the disk is probably fried by then.

Can the clutch slip in normal operation? yes, by manipulating the clutch pedal you manipulate the clamping pressure which LOCKS it into place. So there is some slip transitioning from engaged to not engaged. But besides that there should be no slip.

Don;t really know what else to say. The person who I quoted as spot on is still..spot on. An engaged clutch does not slip. Yes it is not mechanically welded or bolted together (would defeat the point of a clutch), but it does lock into a 1:1 through the force exerted by the pressure plate and friction material of the clutch.

Can an engaged clutch slip under certain conditions? Yes, like if it is failing or overheating or there is a material between the flywheel and clutch causing slippage.

You say it's locked, then say it could slip, well, which one is it?? A solid shaft connecting the engine to the transmission can't slip (maybe twist a little...). A set of gears between the engine and transmission can't slip. lf it is locked, it can't slip, ever. An engaged clutch can slip and it doesn't need to be failing or overheating to do so.

A Centerforce Clutch uses weights that increase clamping pressure as the rotational speed of the clutch increases. Increased clamping pressure = more torque capacity, but the clutch doesn't LOCK!

Driving down the highway, yes, the clutch should be holding 100% of the engine's torque.

You are assuming that the clutch needs to be failing in order to slip. This is untrue. If the conditions are right, a clutch can slip. This slip might be as slight as .0001% of a rotation, but the slip is still there. This is because a clutch is not mechanically locked.

My point is, a clutch will never hold 100% of the time. A clutch cannot lock, outside of a "friction lock".

[poomanchu]

Originally Posted by sarguy01

You say it's locked, then say it could slip, well, which one is it?? A solid shaft connecting the engine to the transmission can't slip (maybe twist a little...). A set of gears between the engine and transmission can't slip. lf it is locked, it can't slip, ever. An engaged clutch can slip and it doesn't need to be failing or overheating to do so.

A Centerforce Clutch uses weights that increase clamping pressure as the rotational speed of the clutch increases. Increased clamping pressure = more torque capacity, but the clutch doesn't LOCK!

Driving down the highway, yes, the clutch should be holding 100% of the engine's torque.

You are assuming that the clutch needs to be failing in order to slip. This is untrue. If the conditions are right, a clutch can slip. This slip might be as slight as .0001% of a rotation, but the slip is still there. This is because a clutch is not mechanically locked.

My point is, a clutch will never hold 100% of the time. A clutch cannot lock, outside of a "friction lock".

I have made my points and am not going to regurgitate everything. I have clearly stated when a clutch will slip, and when it will not.

I will say it again, one more time. A properly engaged clutch should not slip. If it is, it either is overheating, has a foreign item between the disk reducing frictions, is failing or has surpassed its maximum torque capacity, basically the engine is overwhelming its clamping power to lock it in place.

If your point is the clutch will not hold 100% of the time while engaged, it is failing. Yes, when you press in the clutch pedal you are releasing that clamping force.

And what exactly are we talking about now? You say it slips all the time, then no you didnt mean that, only under certain conditions, then a friction LOCK is not a LOCK. The original guy's response correcting your misinformation (as listed below) is correct.

Originally Posted by sarguy01

Technically, there is always a slight amount of slip, at all times, since there is only a friction connection between the flywheel and clutch disk. But, we won't get into that since that amount of slip is probably less than 1%.

This is still false.

BS. It's zero.
A properly working clutch allows zero slippage while engaged. None.
Locked in a 1:1 ratio.
Real world: 1% slippage would be a huge problem for a clutch.

Sorry, you have misinformation and I felt an overwhelming need to educate.

This is still true

Edit: I should have said, "Technically, there is always a slight amount of slip, under certain conditions, since there is only a friction connection between the flywheel and clutch disk."

Define 'certain conditions'. I have named a few conditions which would cause a engaged clutch to slip, yet you reject or bypass them completely.

[sarguy01]

Originally Posted by poomanchu

I have made my points and am not going to regurgitate everything. I have clearly stated when a clutch will slip, and when it will not.

I will say it again, one more time. A properly engaged clutch should not slip. If it is, it either is overheating, has a foreign item between the disk reducing frictions, is failing or has surpassed its maximum torque capacity, basically the engine is overwhelming its clamping power to lock it in place.

If your point is the clutch will not hold 100% of the time while engaged, it is failing. Yes, when you press in the clutch pedal you are releasing that clamping force.

And what exactly are we talking about now? You say it slips all the time, then no you didnt mean that, only under certain conditions, then a friction LOCK is not a LOCK. The original guy's response correcting your misinformation (as listed below) is correct.



This is still false.



This is still true



Define 'certain conditions'. I have named a few conditions which would cause a engaged clutch to clip, yet you reject or bypass them completely.

Please reread my original post. I know that statement is false and reworded it. It now reads, "Technically, there is always a slight amount of slip, under certain conditions, since there is only a friction connection between the flywheel and clutch disk."

I also said in Post #5 and #12 that I miss worded my original post.

How many times shall I say I miss worded it? I made a mistake! I admitted it!

I didn't purposely bypass your mentioned conditions. And, under certain circumstances, as I've mentioned, includes foreign objects, such as sand, dirt, but can also include oil, water, etc. How many of us have a leaky rear main seal? Is it possible that some of that oil can get onto the clutch? Yes. That oil would lower the total holding capacity of the clutch. What if the transmission’s front seal is leaking? Certain circumstances can also include the temp, surface finish/friction material (i.e. a new clutch and a 150,000 mile clutch will not have the same coefficient of friction), inertia of the parts, vibration, rate of torque application, the list goes well beyond my comprehension. Read more here: http://www.pemltd.com/pdf/determining-the-static.pdf

A friction lock is not a physical lock. When someone "locks" their brakes, is there some pin or pawl that engages the brakes? No, but friction can hold the brake rotor. But since friction is "locking" (holding, clamping) the brake rotor, it can still be turned if enough torque is applied to overcome the holding power of the brake's friction. But, the brake rotor isn’t technically locked, is it?

I don't like using the word lock on a clutch because it doesn't physically lock. Does that explain it better???

I will say it again, one more time. A properly engaged clutch should not slip.

I agree with this. But, SHOULD means there is a chance it COULD slip!!!

Maybe I suck at writing about physics and am not typing out my thoughts clearly enough!

[poomanchu]

Ah ok. Yes, anything from oil to a pole forcefully shoved between can break the friction lock. But a friction lock is still a lock. So many fasteners use nothing but friction, nails for instance, lag bolts, staples. Just as a friction lock can be broken by 'certain circumstances', so can other means of fastening or locking. Gears and bolts can be sheared, welds broken, etc.

[mikeyjd]

Much to do about nothing here..

[mechman600]

If you stand near the edge of a cliff where the ground is slanted 45 degrees, only friction is keeping you from sliding and falling off. I am quite sure that under most circumstances, you could stand near the edge for hours without sliding off. Maybe even days if you didn't fall asleep and fall over. Therefore, it can be said that your feet have a 1:1 ratio with the ground, even though it is only friction keeping them from moving. If not, you would fall off the cliff.

Same thing as an engaged clutch.

[sarguy01]

Originally Posted by mechman600

If you stand near the edge of a cliff where the ground is slanted 45 degrees, only friction is keeping you from sliding and falling off. I am quite sure that under most circumstances, you could stand near the edge for hours without sliding off. Maybe even days if you didn't fall asleep and fall over. Therefore, it can be said that your feet have a 1:1 ratio with the ground, even though it is only friction keeping them from moving. If not, you would fall off the cliff.

Same thing as an engaged clutch.

The corrected statement I provided said under certain circumstances.

So, let's use your example:
Standing on the edge of a cliff at a 45* angle = engaged clutch. No outside factors (wind, rain, rock slides) No Slip. No argument. 1:1.

But, let's add some circumstances that a clutch can face:

Wind gust (wind gust hitting car head on) - Sudden change (rate of torque) - changes the coefficient of friction. The engine has to suddenly add torque to keep the car at the same speed.

Earthquake (driveline vibrations caused by natural frequencies, harmonics, engine shaking, potholes, etc) - vibrations will change the coefficient of friction.

Hot earth? (Just go with this...the flywheel gets hot from repeated use) - changes the coefficient of friction.

Worn hiking shoes (worn clutch disk, pressure plate and flywheel surface) - will affect the overall coefficient of friction and lower the amount of holding power.

Wet ground (Humid? Oil leaking on clutch) - Will surely change the coefficient of friction.

So, under some of these circumstances, would you not agree that a good clutch can slip? By slip, I only mean losing its "1:1" for a moment or two, not slip wildly. All of these circumstances can happen and this is only a list I could come up with in five minutes.

[P-hack]

It is going to be vehicle/driver/condition dependent if it slips a tiny bit outside of normal conditions. I don't understand the fuss? If it slips when it isn't supposed to then fix it.