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Thread: Clutch, tranny problem or bad driver?

  1. #1
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    Clutch, tranny problem or bad driver?

    Since I do not know anyone else with similar car to compare this to, I wanted to ask the wise folks here if it is normal or I might be looking some potential issues with the car. I am obviously very new to my M Roadster and it’s gear box is new to me. While trying to get more familiar with the car and let it breathe a little, especially downshifting into the turns and opening it up in the straight, I have started to be more aggressive on acceleration. I recently noticed the following.
    If heavily accelerate through the gears, say 2,3,4,5, without downshifting first, rpms drop 1-1.5k down with every up shift and goes back up as it accelerates as you would expect it with no noticeable issues. Now to the issue....
    If I am coasting in 3rd or 4th and need to go faster and drop it one gear (or 2 depending on my speed) and flore it, as I get to 4 and shift to 5 my rpms jump right back to 8k as if I am still in 4th and car is not pulling as I would expect it to. Eventually, after I ease off the gas and give it gas again, it seems to catch and start pulling again. Is that a sign of slipping clutch or tranny issues? I have to try this few more times to better describe it, but that’s the jist of it. Powerband or not, it shoots from about 7k to 8.5 (chipped) in under a second and I never hit rev limiter. Sensation is as if my rear spins out, which I very highly doubt LOL.

    Thanks

  2. #2
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    You are describing the classic first signs of the clutch being worn out. When one is suspecting the clutch is going out, the test is to put it in a higher gear, say 4th, or 5th if you have the space to go that fast, and floor it. If the clutch is going out, as the engine gets into it's power band, about 4k, you will see (on the tach), and feel (as if the rear end is spinning out), the engine gain rpm without the car going much faster. Unless there is something causing it, (like poor clutch pedal adjustment keeping the clutch from fully engaging), it is time for a new clutch. It will get worse soon. .... I suspect (I'm not the expert here), that the stock clutch delay valve exposes this problem sooner, as in your case, where you have the rpm higher when downshifting.

  3. #3
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    Clutch, tranny problem or bad driver?

    Also be aware that with the factory clutch-dely-valve in place that you will need to execute slow deliberate shifts, no speed shifts.

    That said this does sound like a case of a worn clutch plate. How many miles? When you replace the pressure plate, clutch disk, and throw out bearing, also replace the engine rear main seal.
    You should also consider replacing the transmission shift detent pins (ZF S5D320Z) while transmission is out. Probably inspect and replace the Giubo also. Unfortunately the Lemforder replacements appear to be NLA, so your choice will be Febi (Bilstein Group) or Meyle.
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    Last edited by bluptgm3; 12-09-2018 at 11:47 AM.

  4. #4
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    Put it in 5 at about 25mph and floor it.. a bad clutch will slip

    Sounds like getting on the throttle before the clutch has engaged to me
    Test it by slowing down your shifting especially when getting back on gear... off throttle, then clutch in, downshift (or upshift...), clutch out, then make sure it "hooks" before getting back on the gas

    I sometimes slip the clutch in my E36 after driving my Z3 for awhile - different engines/transmissions, different driving habits. I just have to make a mental note to let the clutch grab before getting back on throttle, in the S54 it's a little more friendly to me rolling on the throttle earlier. Different clutch engagement points as well.

  5. #5
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    Quote Originally Posted by bluptgm3 View Post
    Also be aware that with the factory clutch-dely-valve in place that you will need to execute slow deliberate shifts, no speed shifts.

    That said this does sound like a case of a worn clutch plate. How many miles? When you replace the pressure plate, clutch disk, and throw out bearing, also replace the engine rear main seal.
    You should also consider replacing the transmission shift detent pins (ZF S5D320Z) while transmission is out. Probably inspect and replace the Giubo also. Unfortunately the Lemforder replacements appear to be NLA, so your choice will be Febi (Bilstein Group) or Meyle.
    Sent from my iPhone using Tapatalk
    There is no clutch delay valve in the M

    A narrow restriction in the hose. But no delay valve.




    Sent from my iPhone using Tapatalk

  6. #6
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    The car is 2001 M roadster with 57K miles. So it is S54. I got it at 55K last year. It was kept in very good shape and was taken cared of through it’s previous 4 owners. It was tracked by owner #2 and has some minor modifications (shark tune, exhaust, short shifter, full body brace). Sounds like too early to have clutch problems, but who knows about owners 3 and 4 and their driving habits. Under heavy acceleration and shifting I do have little burning smell that could only come from the clutch. My shifting habits are to stay off the clutch as much as possible and while I do not just dump it, I quickly move through the gears and depress the clutch during shifting for only about a second or less and only gun it when fully off the pedal. Clutch engages about half way, until it heats up, then I run out of space and shifting becomes hard. But it takes about 30-40 mins of shifting in traffic for that to present itself. I will try recommendations above and come back with my findings. I do know that I need new clutch line and a flush. I will do that first before replacing the clutch and see if it improves. Any clutch recommendations? Maybe replace flywheel to something a bit lighter while at it?
    Last edited by DimrBimmer; 12-09-2018 at 02:20 PM.

  7. #7
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    You'll be amazed what a new line will do

  8. #8
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    Quote Originally Posted by DimrBimmer View Post
    ... as I get to 4 and shift to 5 my rpms jump right back to 8k... after I ease off the gas and give it gas again, it seems to catch and start pulling again. Is that a sign of slipping clutch...
    Quote Originally Posted by DimrBimmer View Post
    ... Sounds like too early to have clutch problems... I do know that I need new clutch line and a flush. I will do that first before replacing the clutch and see if it improves...
    That can help shifting by making sure the clutch releases fully and does not drag. But it will not cure your clutch slippage.
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  9. #9
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    Quote Originally Posted by Vintage42 View Post
    That can help shifting by making sure the clutch releases fully and does not drag. But it will not cure your clutch slippage.
    So if it slips, why does it appear to only do it in 5th? Other gears appear to “hook” fine in lower gears. Revs are the same across the board. Wouldn’t it also slip in other gears under heavy acceleration and fast shifting? You would think with gear ratio it would put more stress on clutch disk in lower gears then the 5th, no? Again, I am just talking out of my ass as I am no mechanic. Just a handyman who gets the general idea how things work. For everything else there is YouTube

  10. #10
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    Youtube is a very poor repair book.

    Your clutch is worn. 5th gear always shows it first. That is because the final gear is where the engine will struggle against the most.

    It may be due to technique, or clutch line, or maybe CDV, but in the end, the friction surface isn't gripping. The disk may be 'glazed' over from overheating, so it may get better with gentle driving, but in the end, clutch will need to be changed.
    -Abel

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  11. #11
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    Quote Originally Posted by DimrBimmer View Post
    So if it slips, why does it appear to only do it in 5th? Other gears appear to “hook” fine in lower gears. Revs are the same across the board. Wouldn’t it also slip in other gears under heavy acceleration and fast shifting? You would think with gear ratio it would put more stress on clutch disk in lower gears then the 5th, no? Again, I am just talking out of my ass as I am no mechanic. Just a handyman who gets the general idea how things work. For everything else there is YouTube
    The car is most resistant to acceleration in 5th gear, that is: at higher speeds, mainly due to air resistance. So the clutch might grip enough to accelerate through the lower gears, but at higher speeds, when the air starts pushing back more, the clutch that is just starting to go out will start slipping. ..... Kind of a different topic, but still talking of air-resistance: Turbo-charged cars sometimes can't even reach full boost in lower gears because there is not enough resistance. The car just "goes" immediately.

  12. #12
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    Eventually you may have trouble making it up a hill. That happened to my Scirocco with 410,000 miles on the original clutch.

  13. #13
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    Quote Originally Posted by DimrBimmer View Post
    So if it slips, why does it appear to only do it in 5th? Other gears appear to “hook” fine in lower gears. Revs are the same across the board. Wouldn’t it also slip in other gears under heavy acceleration and fast shifting? You would think with gear ratio it would put more stress on clutch disk in lower gears then the 5th, no? ...
    Yes, I would think exactly as you do. And I have never to this day heard a satisfying explanation. How can a worn clutch not slip when taking off hard in 1st, and yet slip when applying throttle in 5th at some moderate speed?
    You would think the clutch must transmit more force accelerating in 1st than accelerating in 5th.
    Last edited by Vintage42; 12-09-2018 at 07:14 PM.
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  14. #14
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    Quote Originally Posted by Vintage42 View Post
    Yes, I would think exactly as you do. And I have never to this day heard a satisfying explanation. How can a worn clutch not slip when taking off hard in 1st, and yet slip when applying throttle in 5th at some moderate speed?
    You would think the clutch must transmit more force accelerating in 1st than accelerating in 5th.
    The clutch works hardest when trying to get the car moving in high gear.

    Best explained with an example.

    Think about riding a bicycle. If you put it in top gear and try to get it moving you have to apply a lot more force to the pedals than when you do the same in the lowest gear.

    Lower gears make it easier for the engine to turn the wheels. When the engine works less hard, the clutch does too.
    Last edited by BruceWarne; 12-09-2018 at 09:08 PM.

  15. #15
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    Quote Originally Posted by Vintage42 View Post
    Yes, I would think exactly as you do. And I have never to this day heard a satisfying explanation. How can a worn clutch not slip when taking off hard in 1st, and yet slip when applying throttle in 5th at some moderate speed?
    You would think the clutch must transmit more force accelerating in 1st than accelerating in 5th.
    The satisfying explanation is 2 posts above yours. It "feels" like the car and clutch are under more force in lower gears because the car is easier to accelerate at lower speeds. (easier to accelerate = less tendency to make the clutch slip). It "feels" like the car is under less force in higher gears because the car is resisting acceleration more, thus harder to accelerate at higher speeds. (harder to accelerate = more tendency to make the clutch slip). Another way to help understanding: the engine produces the same torque at a certain rpm regardless of what gear the car is in. So, why does the car accelerate so much faster in lower gears? Answer: less resistance.

  16. #16
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    I like Bruce’s explanation referencing gears on a bycicle. Makes more sense to my non-mechanic mind. I still find it difficult to comprehand that wind/air resistance would cause enough drag to cause clutch slippage. While gearing makes more sense. It obviously takes much harder to pedal a bike when on smaller sprocket (higher gear) at any speed. Especially when trying to accelerate. I have ripped apart my bike chain once doing exactly that. I guess either version easily proven/disproven if slipping could be replicated on a dyno...
    Last edited by DimrBimmer; 12-09-2018 at 11:16 PM.

  17. #17
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    Quote Originally Posted by DimrBimmer View Post
    I like Bruce’s explanation referencing gears on a bycicle. Makes more sense to my non-mechanic mind. I still find it difficult to comprehand that wind/air resistance would cause enough drag to cause clutch slippage. While gearing makes more sense. It obviously takes much harder to pedal a bike when on smaller sprocket (higher gear) at any speed. Especially when trying to accelerate. I have ripped apart my bike chain once doing exactly that. I guess either version easily proven/disproven if slipping could be replicated on a dyno...
    Except that the gearing explanation is not a good analogy. The bicycle analogy would have to be: at the same pedal rpm (not at the same speed as Bruce implies), compare a lower gear to a higher gear. The lower gear is easier to pedal. Why is a bike easier to pedal, at the same pedal rpm, in a lower gear than a higher gear? Answer: less resistance. The added resistance in higher gears comes mainly from pushing more air as you move faster, just like a car. If you could ride in a vacuum, and had zero-friction bearings/tires, it would be just as easy to pedal at high speeds as it would be at lower speeds. Stick your hand out of the car window at 5 mph, then do it at 100 mph. You will feel tremendous force. Your car is feeling a lot more than that.

  18. #18
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    Quote Originally Posted by zellamay View Post
    Except that the gearing explanation is not a good analogy. The bicycle analogy would have to be: at the same pedal rpm (not at the same speed as Bruce implies), compare a lower gear to a higher gear. The lower gear is easier to pedal. Why is a bike easier to pedal, at the same pedal rpm, in a lower gear than a higher gear? Answer: less resistance. The added resistance in higher gears comes mainly from pushing more air as you move faster, just like a car. If you could ride in a vacuum, and had zero-friction bearings/tires, it would be just as easy to pedal at high speeds as it would be at lower speeds. Stick your hand out of the car window at 5 mph, then do it at 100 mph. You will feel tremendous force. Your car is feeling a lot more than that.
    While air resistance is certainly a factor, gearing has a significant impact. Both of course come into play and a LOT sooner than folks would think. When I was training for Ironman (and doing Ironman) I would consistently gain 2 mph on the bike (from 18-20ish mph) by going into the aero position. We're talking about a relatively small reduction in frontal area (6" on either side and about 6" in height) and slight improvement in Cd. Same effort, gain 10%. Aero resistance becomes into play much sooner than people think, but the mechanical advantage of gearing is not insignificant either.
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  19. #19
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    Quote Originally Posted by zellamay View Post
    The satisfying explanation is 2 posts above yours... air resistance... why does the car accelerate so much faster in lower gears? Answer: less resistance... .
    I had read that before posting, but it was not satisfying to me in explaining clutch slippage. The bicycle, maybe.
    Last edited by Vintage42; 12-10-2018 at 08:19 AM.
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  20. #20
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    Any physics professors drive a z and on this board? We could certainly use one right now. Honestly, as already been said, I am sure both wind/air resistance and gearing come into play. Air resistance + gearing resistance = higher gear clutch slippage. That said, I am switching “gears” of the thread back to original post and question. Any recommendations for clutch replacement and maybe lighter flywheel? I am bringing my car to a mechanic soon to do all bunch of stuff. Maybe have him swap the clutch while at it.
    Thanks!
    Last edited by DimrBimmer; 12-10-2018 at 08:19 AM.

  21. #21
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    The clutch sees engine torque. Only. Engine torque, for a given engine, is controlled by the amount of fuel in the cylinder per stroke. Only. There is no gear shift lever position sensor in the clutch system. What is being observed is down to delta-T and driver input. The driver is more willing to apply larger throttle for longer in a higher gear.


    /.randy

  22. #22
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    Quote Originally Posted by DimrBimmer View Post
    ... I guess either version easily proven/disproven if slipping could be replicated on a dyno...
    So the clutch slips when accelerating in 5th when loafing along at 40 mph, then hooks up and chirps the tires after a power downshift to 2nd.
    Would the dyno explain why the clutch slips under low power and torque in the first case, and does not slip under high power and torque in the second case?

    So if you start off in 5th with enough revs, a bad clutch slips and the engine does not die. If you start off in 1st, the bad clutch does not slip and can burn rubber.
    What would a dyno make of that?
    Last edited by Vintage42; 12-10-2018 at 02:03 PM.
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  23. #23
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    Quote Originally Posted by rf900rkw View Post
    The clutch sees engine torque. Only.
    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.
    George Roffe
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  24. #24
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    Quote Originally Posted by Geo31 View Post
    ... 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.
    So when the friction disk loses it grip for whatever reason, why does it slip in 5th and not 1st?

    I restored and forumed pre-'70 BMW bikes. Dry clutches between a rear main seal and a transmission input seal. When the seals would leak, oil would drip from a hole under the bell housing. Eventually oil would make its way to the clutch and be slung out over the friction disk. And the first symptom would be slippage in top gear.

    I go with Randy's explanation in #21.
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  25. #25
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    [QUOTE=Vintage42;30161684]So when the friction disk loses it grip for whatever reason, why does it slip in 5th and not 1st?

    Because the car resists acceleration more in 5th than in 1st. As Randy said, the clutch does not know what gear the car is in. It knows 2 things: 1) how much torque is being applied on the engine side. 2) how much resistance is being applied on the d.s. side. The torque is the same in 5th as it is in 1st (unlike the bicycle analogy). 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.

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