What factors determine Clutch wear?

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Angelbroken
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What factors determine Clutch wear?

Post by Angelbroken »

Hello again guys! . . . So I drove by a vehicle today with its hazard lights flashing and the two people standing around it inspecting it. As I drove by I smelled a heavy, HEAVY burnt paper smell. (Instantly reminded me of what people say a 'burning clutch' smells like) and got me wondering what exactly wears the clutch out most. . . Is it high speeds? high RPM? or a combination.

My dad, (who's driven standard all his life) gave me the analogy that using the clutch is like 'sticking your foot out the door and dragging it on the ground' as you drive. At low speeds, your shoe won't get ripped off all that fast, but at 60mph, your shoe (and your leg) will be ripped off pretty fast.

So is speed alone all that determines clutch wear? Or is engine RPM somehow a factor? Like would using the clutch at 3000RPM and 50mph be worse then 50mph and idle RPM (980 for me)? Or is it just as simple "How fast you're going".

Oh, and Im not really looking for a "riding the clutch is the worst" answer, becuase even in the fastest shift the clutch is still 'used' for even a fraction of a second. I'm trying to figure out what factor wears the most during that fraction of a second. :lol:
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Re: What factors determine Clutch wear?

Post by theholycow »

Road speed is irrelevant. "Speed" when talking about a clutch is engine speed and/or input shaft speed.

Here are the factors: RPM difference between clutch and flywheel, pressure, time, temperature of clutch (though that last one is really a function of the first 3 anyway).

If you drag your shoe lightly out of the car at 6mph it won't get ripped off.
If you drag your shoe heavily out of the car at 6mph it will get ripped off.
If you drag your shoe lightly out of the car at 60mph it will get ripped off.
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Re: What factors determine Clutch wear?

Post by watkins »

Youre a cow. You know nothing of shoes. Unless you become one...
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Re: What factors determine Clutch wear?

Post by theholycow »

That's why I wear sandals.

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watkins wrote:Humans have rear-biased AWD. Cows have 4WD
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Re: What factors determine Clutch wear?

Post by watkins »

Where in the name of all things bovine-devine did you get that?
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Re: What factors determine Clutch wear?

Post by Angelbroken »

Hmm. . .Okay - but how do you use a clutch 'roughly'? I mean what determines if the clutch is being used in a "foot dragging lightly" or "foot dragging heavily" sort of way?
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Re: What factors determine Clutch wear?

Post by bk7794 »

correct me if I am wrong, but my basic understanding is if your using the clutch as a foot rest and its slipping the entire way down the highway, That would be determined in my eyes as dragging it heavily. So if the clutch is not adjusted right this might happen.

I think slipping it heavily with your foot planted at like 7000rpm and slipping the clutch would be like sticking your foot heavily into the ground...correct me if I am wrong though please.
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Re: What factors determine Clutch wear?

Post by AHTOXA »

A properly working clutch, once engaged doesn't care how fast a vehicle goes or how fast the motor turns. It is not slipping at that point.
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Re: What factors determine Clutch wear?

Post by theholycow »

Angelbroken wrote:Hmm. . .Okay - but how do you use a clutch 'roughly'? I mean what determines if the clutch is being used in a "foot dragging lightly" or "foot dragging heavily" sort of way?
Looking back at what I posted about it:

RPM difference between clutch and flywheel - Generally this happens during high RPM launching. Car is at a stop, you rev up to 4000RPM (or worse) and start to engage clutch. One botched (or unskilled racing) launch isn't going to cut your clutch life in half but I wouldn't recommend doing it anyway.

Pressure - You're engaging the clutch and you hold it almost fully engaged where it's still slipping a little. I can't imagine anyone ever doing this. It's certainly not something you'll do accidentally. The only realistic scenario is when your clutch is worn out or your engine is upgraded, and you push more torque through it than it can hold. You needn't worry about this.

Time - You start to launch and pause your clutch foot where it's slipping...and never continue engaging the clutch. A realistic, and harmless, situation would be when you're stuck in slow moving uphill traffic and need to crawl at very low speed. Again I can't imagine a realistic situation (other than harmless ones).

Temperature of clutch - This is mainly a function of the other issues, but one way it could happen without doing anything wrong would be in aggressive stop-and-go traffic...launch brake honk brake honk launch brake launch brake launch honk honk middle finger launch brake racial slur launch road rage brake launch...

You could have all of those issues at once if you're towing a trailer that's too heavy for your vehicle in mountainous terrain with lots of stop signs.
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Re: What factors determine Clutch wear?

Post by tankinbeans »

bk7794 wrote:
I think slipping it heavily with your foot planted at like 7000rpm and slipping the clutch would be like sticking your foot heavily into the ground...correct me if I am wrong though please.
If you're revving at 7000rpm and drop the clutch it is then completely disengaged. In this state, it doesn't care and your car will begin to slow. The only thing that is undergoing any strain, and I've read that it's fairly minimal strain, is the throw-out bearing. Some advise to wait at a light in neutral, clutch up, to prevent strain on the bearing; I don't because I'm not yet comfortable timing everything correctly to drop it in gear without undo fingers and beeping.

Somebody else will probably further explain my own n00b assertions.
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Re: What factors determine Clutch wear?

Post by theholycow »

That's all correct. If the clutch pedal is all the way down to the floor, then there is no friction and you can rev all you want without fear of hurting the clutch.

Also, I forgot to address this bit earlier:
bk7794 wrote:correct me if I am wrong, but my basic understanding is if your using the clutch as a foot rest and its slipping the entire way down the highway, That would be determined in my eyes as dragging it heavily. So if the clutch is not adjusted right this might happen.
You'd need to have a heavy foot resting on it to make it slip. The usual way people rest their foot on it doesn't move the pedal enough to make it slip, but may move the pedal enough to put the throwout (technically called "release") bearing to work when it should be at rest. Either way it's not a good idea, when cruising your left foot should not be touching the clutch pedal.
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Re: What factors determine Clutch wear?

Post by bk7794 »

I shouldn't have said rest their foot on the clutch, but I get what you mean. But if you are slipping it while lets say going 75mph in 4th gear and the engine is revving at lets say 7000RPM. When it is slipping it would be having a caliper stuck in the grabbing position. Right? So that would wear it down and potentially...no actually overheat it right?


haha my posts just seem so out of place.
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Re: What factors determine Clutch wear?

Post by theholycow »

Yup, that would be quick destruction as you describe.
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Re: What factors determine Clutch wear?

Post by Rope-Pusher »

Slipping will cause overheating, which will/can cause glazing.
Evidence of overheating is normally a color change, like patches of blue below:
Image
The amount of heat generated is related to how long it was slipping and at what rpm it was slipping. Low speed slippage typically generates less heat than high speed slippage. The temperature is related to the energy of the slippage heat, the initial temperature before slippage, and the thermal mass of the components. More massive flywheels and pressure plates tend to protect the clutch disk from getting to a high enough temperature to glaze the friction material. The heat from a little slippage at launch is generally absorbed by the flywheel and pressure plate, especially if they started out relatively cool. Continuous high speed slippage will tend to supply enough heat to overcome the thermal inertia of the components and reach very high temperatures.
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Re: What factors determine Clutch wear?

Post by Angelbroken »

theholycow wrote:
Angelbroken wrote:Hmm. . .Okay - but how do you use a clutch 'roughly'? I mean what determines if the clutch is being used in a "foot dragging lightly" or "foot dragging heavily" sort of way?
Looking back at what I posted about it:

RPM difference between clutch and flywheel - Generally this happens during high RPM launching. Car is at a stop, you rev up to 4000RPM (or worse) and start to engage clutch. One botched (or unskilled racing) launch isn't going to cut your clutch life in half but I wouldn't recommend doing it anyway.

Pressure - You're engaging the clutch and you hold it almost fully engaged where it's still slipping a little. I can't imagine anyone ever doing this. It's certainly not something you'll do accidentally. The only realistic scenario is when your clutch is worn out or your engine is upgraded, and you push more torque through it than it can hold. You needn't worry about this.

Time - You start to launch and pause your clutch foot where it's slipping...and never continue engaging the clutch. A realistic, and harmless, situation would be when you're stuck in slow moving uphill traffic and need to crawl at very low speed. Again I can't imagine a realistic situation (other than harmless ones).

Temperature of clutch - This is mainly a function of the other issues, but one way it could happen without doing anything wrong would be in aggressive stop-and-go traffic...launch brake honk brake honk launch brake launch brake launch honk honk middle finger launch brake racial slur launch road rage brake launch...

You could have all of those issues at once if you're towing a trailer that's too heavy for your vehicle in mountainous terrain with lots of stop signs.
watkins wrote:Where in the name of all things bovine-devine did you get that?
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Hmm. Thanks cow; based on your descriptions, I don't think I have ever done any of those things. Even in heavy rush hour, the longest time my clutch slips is 1-2 seconds at most. I'm a pretty moderate driver, so if there's anything I'm guilty of, it's taking my time driving =P
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