How does the clutch not face the most resistance in high gear?
It does, but as long as the tires don’t slip the clutch sees the same resistance.
The transmission multiplies the torque differently depending on which gear it’s in. 300 lb-ft in gets maybe 750 out in first gear. 300 in gets 300 out if the transmission is in high gear.
If the clutch slips at 100 lb-ft you still get 250 out in first gear. And 100 lb-feet in high gear. If 150 lb-ft is needed at the output (drive wheels) the clutch will slip in high gear but not first gear.
But the clutch is between the engine and transmission. It only see the max torque the engine produces. So 300 lb ft or 100 lb ft, if the tires don’t slip the clutch sees the same torque across it. If the tires slip, it sees less torque.
This is like those trick questions in high school science class: If you weigh 150 pounds on your bathroom scale, what would your scale read if you placed it on top of another identical scale?
Both of those statements are true. But there’s more to this. If the torque were always the same there’d be no need for different gear ratios in the transmission. Starting in high gear would work as well as starting in low.
Why does the engine labor at 20 MPH going uphill in high gear but not at the same speed in low gear if the torque is the same?
2 reasons… In high gear the engine’s rpm is so low it doesn’t produce much torque. And because the torque multiplication through the gearbox doesn’t put as much torque to the wheels.
You can’t work this backwards.
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The engine makes plenty of torque when you get up to speed. In my experience it is far, far easier to test a weak clutch in high gear. If it slips in low it’s total toast.
Okay, perform the experiment at the same RPM then. If 150 lb-ft at the wheels is required to move the car and the transmission is in first gear then the clutch sees only 60 lb-ft, the torque is then multiplied by the transmission so the output is 150 lb-feet. In high gear to get 150 lb-ft you’d need to put in 150 lb-ft. The clutch sees all of that.
You’re simply denying the torque multiplication of the transmission.
If it slips at all in any gear it is still toast
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I am not denying it, I am telling you it does not matter. If you develop 150 lb ft at the wheel (the ground develops force not torque) and 60 at the clutch, and it doesn’t slip. That doesn’t mean the clutch is good if it slips at 150 lb ft now does it?
The entire point of the test is to apply the max torque the engine can supply to the clutch to see if it slips. The resistance of the transmission at the input shaft is the result. The gear selected does not matter.
The gear selected DOES matter. In a lower gear a marginal clutch can pass enough torque to spin the tires without slipping. In high gear a marginal clutch will slip.
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By the way, does the above look familiar? Still want to say the gear selected doesn’t matter?
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That was a reply to the OP who did not notice slipping until 5th gear. It should have been noticeable before that.
Remeber I also said this…
I believe manual transmissions do not multiply torque. Only torque converters, (as those found in automatic trans), can do that because of the stator, but only when slipping and the stator comes into play.
The clutch sees the torque produced at any instant. If is then multiplied by the transmission. If the drive wheels spin because of the multiplied torque then the clutch will see less torque. If the transmission is in a higher gear the torque will not be mulitplied and the clutch can slip if marginal.
Really? What do you suppose the gear reduction does, then?
Only by the engine
Yes
Yes. So the clutch won’t slip because the tires do first. I again remind you of this…
The torque at the clutch is only supplied by the engine. It is ONLY resisted by the tires in any gear. If the engine revs beyond what it should in any gear while the tires are gripping the road, the clutch is slipping. Whether it is in 1st gear or 5th gear the effect is the same.
Agreed.
The resistance to tire rotation that the engine sees will depend on what gear the transmission is in. It’s easier to get the tire rotating in low gear than it is in high gear. Surely you agree to that. That resistance is overcome by the torque at the output end of the transmission. The output torque of the transmission is a product of the input torque multiplied times the transmission’s gear ratio.
The input torque is what the clutch sees.
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The gear reduction in a transmission puts more torque at the wheels because of the higher engine rpm for a given road speed. It also lowers the amount of force needed to move a vehicle forward, since lower gears move the vehicle at lower speeds.
The stator in the torque converter enables torque multiplication with the rest of the gear train ratios staying fixed.
If you’re going to say that the gears lower the torque, then you’ll need to also say the differential gearing also lowers torque, and getting smaller tires also lowers torque.
Maybe we’re arguing over simple symantics, gear reduction vs torque multiplication.