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Thread: Clutch, tranny problem or bad driver?

  1. #26
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    Quote Originally Posted by zellamay View Post
    ... The torque is the same in 5th as it is in 1st... The difference is that in 1st gear 3000 rpm is at a low speed, but in 5th gear 3000 rpm is at a much higher speed. ... At higher speeds, the car resists acceleration much more, due mainly to air pressure, and also from increased friction from bearings and tires and greater resistance of rotating parts to rotate faster.
    The torque curve rises and maxes with RPM in any gear, not related to MPH speed. I don't see how air pressure or bearing friction etc are involved in clutch slippage. I don't think clutch slippage is related to external forces, such as speed and resistance.

    I think the slippage is caused by the torque into the friction plate. It's just hard to understand how a clutch can apply full power starting off in 1st while slipping at low RPM in 5th.
    Last edited by Vintage42; 12-10-2018 at 06:22 PM.
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  2. #27
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    Quote Originally Posted by Vintage42 View Post
    The torque curve rises and maxes with RPM in any gear, not related to MPH speed. I don't see how air pressure or bearing friction etc are involved in clutch slippage. I don't think clutch slippage is related to external forces, such as speed and resistance.

    I think the slippage is caused by the torque into the friction plate. It's just hard to understand how a clutch can apply full power starting off in 1st while slipping at low RPM in 5th.
    If you go back to bycicle gear box example. Assuming that instead of you pedaling your front sprocket is connected to an engine. It would be much harder to turn the wheel if you are in the higher gear then if you are in the lower gear. This, friction plate slipping due to force required to move the higher gear. Even if you are moving already, it is still harder to pedal in higher gear then lower. I also don’t think that clutch slippage has little to do with an oncoming air resistance. Maybe little. All that air resistance tells me is that you would go slower at the same rpms. I guess it still plays role on how soon and how much slippage you would get. But so is the drag caused by tires diameter and how much you had for bfast. Putting you car on a dyno although gets rid of air drag, it still has the tire resistance to deal with. Regardless this argument will never stop until we get someone with PhD in Physics join the thread.
    Last edited by DimrBimmer; 12-10-2018 at 06:51 PM.

  3. #28
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    When I started driving, cars had big strong bumpers, and some bad clutches. A test was:
    Put the bumper against a wall and try to push the wall over in top gear. The clutch would slip and the engine would race.
    Try that in first gear. The engine would stall.
    A bad clutch could not hold the torque.
    Last edited by Vintage42; 12-10-2018 at 07:53 PM.
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  4. #29
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    I give up.

  5. #30
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    Quote Originally Posted by zellamay View Post
    I give up.
    So quickly? LOL. And I was hoping we were going to brake reply record here. Not!
    I do want to know what are my options for 2001 m roadster as far as clutches and flywheel go. I am not planning on getting turbo or supercharger anytime soon or ever. But do plan on taking the car to a track few times per year. So while I do not need a race clutch, I am wondering what folks here are using for aftermarket clutch options.
    Last edited by DimrBimmer; 12-10-2018 at 10:46 PM.

  6. #31
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    You are confusing the power source with the power drains. If the clutch lets go at, say, 150 ft-lb, it is going to let go at 150 ft-lb in 5th gear or 1st gear. All the rest of your list are items that explain why the driver did not order up enough torque in 1st gear, not why the clutch can magically hold better.



    Quote Originally Posted by Geo31 View Post
    Nicht so.

    When the pressure plate engages the clutch disc and flywheel, the clutch sees both the engine torque and the resistance of inertia at the wheels, which is governed by aero, mass, and mechanical advantage (gearing) and to a lesser extent, other losses.


    /.randy

  7. #32
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    The bicycle analogy is very flawed. You are looking at horsepower, not torque. What matters is the force being applied to the pedal crank (the equivalent position as our clutch), not how fast or easily the bike accelerates. If you stand on the pedal with all your weight, the TORQUE at the pedal shaft is the same, no matter what gear you are in.


    /.randy

  8. #33
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    Quote Originally Posted by rf900rkw View Post
    ... the clutch lets go at, say, 150 ft-lb, it is going to let go at 150 ft-lb in 5th gear or 1st gear..
    That sounds spot on. Regardless of the gear you are in, it would always slip at same amount of torque. Come to think of it, going back to my original post, I am pretty sure I experienced the same in 4th gear as well while being a led-foot... so, I am pretty sure replacing clutch is in my near future if I want to occasionally track the car. Now if someone could recommend good aftermarket clutch and flywheel combo.

  9. #34
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    I tried. I really tried. ... What causes clutch slipping is not just torque. It is the combination of torque applied on one side of the clutch, ... AND ... resistance applied on the other side of the clutch. If there was no resistance, the clutch would not slip no matter how much torque was applied. ( I know I sound like a broken record, and wish I could say it better, but: ) the reason the clutch slips sooner in higher gears , at the same rpm/torque, is that there is more resistance in higher gears. ..... P.S. I suggest a SMF, and a light one. Dual mass flywheels are just another mechanical thing, and lightweight makes the car more fun to drive, letting the engine respond much quicker to throttle input when shifting.
    Last edited by zellamay; 12-11-2018 at 02:47 PM.

  10. #35
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    I remember hearing folks discuss clutch chatter issues after installing lighter flywheels. I don't know if a different pressure plate was used in these instances, though.
    Tony
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  11. #36
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    Quote Originally Posted by ProductUser View Post
    I remember hearing folks discuss clutch chatter issues after installing lighter flywheels. I don't know if a different pressure plate was used in these instances, though.
    Yes, I read about that too. Many cars come from factory with SMFs and don't chatter, so I wonder why BMWs would chatter if one also uses a sprung-hub clutch? I think, from reading, that a sprung-hub clutch is necessary and solves a lot of that problem, so I'll use one.

  12. #37
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    The gear ratio of the transmission MULTIPIES the torque to the rear wheels from the engine. and the clutch is before the trany so it only see engine torque. First has the highest gear ratio, (about 5 to 1) , fifth is normally about 1 to 1. The clutch hold power is measured in torque (ft lbs).

    Making up some number, let say we need 200 ft lbs to the rear wheels to burn the tires and the clutch will hold 150 ft lbs of torque. In first gear we need 200 ft lb / 5(gear ratio) or 40 ft lbs from the clutch/engine to burn rubber. In fifth, we can NOT do it because the gear ratio is 1 to 1 and we would need 200 ft lbs from the clutch/engine but the clutch slips at 150 ft lbs. so the clutch will slip. From a previous post, the " resistance " is the torque applied to the gearbox/wheels to burn the tires (this is multiplied by the gear ratio), the engine supplies the torque to the other side of the clutch. Clutches are measured by the amount of torque they will hold, nothing else.

    Clutch chatter is related to the friction between the clutch and the pressure plate/flywheel. You want the clutch to slip smoothly on the pressure plate when being released. If the binding force is too much, the clutch will start to grab and chatter. Very common on high torque race clutch setups. I had one, you always had a bit of chatter and sometime it just grabbed and you had to quickly depress the clutch to avoid jumping forward. Not a good street setup. It is really hard to beat the stock setup if you want a smooth clutch action.
    Last edited by Adker; 12-11-2018 at 11:27 PM.

  13. #38
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    Quote Originally Posted by zellamay View Post
    I tried. I really tried. ... What causes clutch slipping is not just torque. It is the combination of torque applied on one side of the clutch, ... AND ... resistance applied on the other side of the clutch. If there was no resistance, the clutch would not slip no matter how much torque was applied. ( I know I sound like a broken record, and wish I could say it better, but: ) the reason the clutch slips sooner in higher gears , at the same rpm/torque, is that there is more resistance in higher gears. ..... P.S. I suggest a SMF, and a light one. Dual mass flywheels are just another mechanical thing, and lightweight makes the car more fun to drive, letting the engine respond much quicker to throttle input when shifting.

    If there is no resistance, there is no torque. Try this. Place a nut on the table and try to tighten it with a torque wrench. Can't, can you? No resistance, no torque.

    And this is the issue here. The engine supplies the torque. The driver controls the engine. It is much easier for the driver to apply sufficient torque in a higher gear. And things happen slower so it is easier to observe. But the clutch only sees engine torque and will slip at a given torque no matter the gear

    Proper test for clutch slippage. look up your engines torque peak RPM. Sweep the engine through that RPM band at full throttle in whatever gear is most comfortable.



    On the clutch itself. The Gripforce stage 2 single mass kit was/is very popular with the forced induction guys. It's cheap, and works in the power range we're talking here. The only caveat is some examples have shown a tendency to chatter when hot. Oh, and they create a bunch of gear rattle at idle... especially in the Getrag boxes.


    /.randy

  14. #39
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    [QUOTE=rf900rkw;30162803]

    Proper test for clutch slippage. look up your engines torque peak RPM. Sweep the engine through that RPM band at full throttle in whatever gear is most comfortable.

    Are you saying that you don't agree with the concept that it is easier to see early signs of clutch slippage in a higher gear?

  15. #40
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    And is it true that if the clutch begins to slip when throttle is applied at speed in 5th gear, like maintaining speed up an Interstate hill, it will stop slipping if you downshift to a lower gear?
    Last edited by Vintage42; 12-12-2018 at 12:10 PM.
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  16. #41
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    Quote Originally Posted by Vintage42 View Post
    And is it true that if the clutch begins to slip when throttle is applied at speed in 5th gear, like maintaining speed up an Interstate hill, it will stop slipping if you downshift to a lower gear?
    I ll take that one.
    In lower gear there is less resistance to move same mass up the hill. Same with bycicle gear scenario. What do you do on the bike when going up the hill? You downshift. If bycicle gear box had tendency to slip, it would have in higher gear up the hill. Thus, engaging lower gear lowers the resistance and chance of slippage. Well, that’s how I understand it.

  17. #42
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    Quote Originally Posted by DimrBimmer View Post
    ... engaging lower gear lowers the resistance and chance of slippage. Well, that’s how I understand it.
    The air resistance at 70 mph going up an Interstate hill is not changed by engaging lower gears.
    But as I understand Adker's Post #37, downshifting does reduce the torque handled by the clutch.
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  18. #43
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    Quote Originally Posted by DimrBimmer View Post
    I ll take that one.
    In lower gear there is less resistance to move same mass up the hill. Same with bycicle gear scenario. What do you do on the bike when going up the hill? You downshift. If bycicle gear box had tendency to slip, it would have in higher gear up the hill. Thus, engaging lower gear lowers the resistance and chance of slippage. Well, that’s how I understand it.
    In a lower gear, there is not "less resistance to move the same mass up the hill". All resistance factors remain the same in any gear: weight, friction, wind, kinetic energy, etc. When you change gears, bicycle or car, you are simply moving the engine (gasoline or human legs), into it's better rpm range.

    - - - Updated - - -

    Quote Originally Posted by Vintage42 View Post
    The air resistance at 70 mph going up an Interstate hill is not changed by engaging lower gears.
    But as I understand Adker's Post #37, downshifting does reduce the torque handled by the clutch.
    I don't see how downshifting would reduce the torque experienced by the clutch. You still have the same resistance, and the same force driving it (assuming you are maintaining constant speed).

  19. #44
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    Quote Originally Posted by zellamay View Post
    In a lower gear, there is not "less resistance to move the same mass up the hill". All resistance factors remain the same in any gear: weight, friction, wind, kinetic energy, etc. When you change gears, bicycle or car, you are simply moving the engine (gasoline or human legs), into it's better rpm range.
    By resistance I mean resistance of the clutch against the plate before it starts to slip. But whatever. I think I give up already myself. I just want to know where I am going to find additional $2k to replace my clutch. Hmmmm... Santa?!?

  20. #45
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    The magic of mechanical advantage...WheelTorque=MotorTorque × Gear ratio

    And that is all I have to say
    Last edited by Adker; 12-12-2018 at 02:57 PM.

  21. #46
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    Quote Originally Posted by Adker View Post
    The magic of mechanical advantage...WheelTorque=MotorTorque × Gear ratio

    And that is all I have to say
    Wouldn’t glazed clutch be a variable in there somewhere?

  22. #47
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    The equation shows how much torque is available, the clutch just limits the maximum torque value. A glazed or worn clutch would just lower the original operational torque of the clutch. At some point, it just slips with any torque. I have seen cars that would not move because they used the clutch while slipping and burned up the friction material, what a horrible smell.

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