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      09-12-2010, 07:56 AM   #1
dekaliber
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"Rubber-banding" effect in 1st

I thought this was normal for these cars, or otherwise a result of occasionally sloppy driving, but a BMW CCA instructor commented on this yesterday when he drove my car at pre-tech so I thought I'd get some opinions.

Once engaged in 1st gear, does anyone else notice an occasional "rubber-banding" effect in the driveline as you depress the accelerator, where power delivery is uneven and it takes a second for the car to rev freely? I want to say it's mostly clutch-related, because it was much, much worse with the CDV, and virtually unnoticeable in the Z4 3.0si, which has a different clutch altogether. Since the CDV replacement and ~2500 miles of practice on the M, it doesn't happen with the same severity or frequency. It does not happen in any gear beyond first. It also doesn't happen if I launch more aggressively, which probably explains why it didn't seem to be as prevalent in the cars I test drove, because I was definitely a bit more spirited on those drives (without being abusive, of course).
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      09-12-2010, 10:13 AM   #2
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The only time I've experienced this is on very cold mornings, say below 40F, and only lasts until I'm into 2nd and does not repeat.
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      09-12-2010, 10:05 PM   #3
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It happens to me as well.
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      09-12-2010, 11:47 PM   #4
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Maybe symptomatic of drive-by-wire. I haven't noticed, but will start paying attention.
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      09-13-2010, 12:58 AM   #5
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I thought it was just drive-by-wire as well. I hear that an ECU tune smooths out throttle response though throughout the entire rev-range too =]
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      09-13-2010, 04:36 AM   #6
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I've had it happen occasionally on cold starts. It rarely occurs once the car has warmed up.
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      09-13-2010, 06:43 AM   #7
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I get it too. I just take it as a peculiarity of the adaptive drive by wire throttle pedal.. I do a lot of driving in stop-start traffic and i think that messes up the mapping making it lethargic and "soft". I've found that resetting the throttle mapping adaptation every now and then helps a lot.
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      09-13-2010, 07:25 AM   #8
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IIRC, the M has the same tranny as the 3.0si

also when was the last time you changed your air filter?
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      09-13-2010, 11:43 AM   #9
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Quote:
Originally Posted by mike87 View Post
IIRC, the M has the same tranny as the 3.0si

also when was the last time you changed your air filter?
i'm assuming a clogged air filter may cause the 'jerkiness' in engaging first gear? fwiw, i've checked my air filter and do still occassionally notice the rubberbanding gear engagement in first.
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      09-13-2010, 12:01 PM   #10
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wait, what air filter? I'm confused...
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      09-13-2010, 08:41 PM   #11
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Quote:
Originally Posted by mfanatic325 View Post
wait, what air filter? I'm confused...
The paper intake air filter I believe. I checked mine a few weeks ago and it still looked pretty clean, although I was able to shake out a decent amount of dust. A new one is on the way, just in case.

Still, I don't think it's an engine or throttle-related issue. The rubber-banding effect is not unlike what happens when someone is trying to learn how to drive stick, but that's not really an issue in this case. My 3er is buttery smooth in any gear, and it has the same ZF unit as the M and 3.0si as far as I can tell. As mentioned, it doesn't really happen with a more aggressive launch at slightly higher (2000+) RPM, which leads me to think that it's something to do with the clutch, particularly when engaged at lower (normal?) engine speeds.
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      09-13-2010, 11:33 PM   #12
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ohhh icic. I hadn't quite seen the correlation between air filter & car behavior until just now lol..

anyhow, yeah I'm pretty certain it's just the difference between the ECU's and throttle mapping. Hence why people have reported that after an ECU tuning/upgrade, the throttle and power delivery is a lot smoother throughout the rev band, regardless of what gear you're in. Probably even in Reverse jk haha
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      09-13-2010, 11:43 PM   #13
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Are you saying you floor the car and it doesn't seem to give you full acceleration for a second? That's not normal. S54 is a very responsive engine, it was built specifically NOT to act that way.
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      09-13-2010, 11:47 PM   #14
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Quote:
Originally Posted by O-cha View Post
Are you saying you floor the car and it doesn't seem to give you full acceleration for a second? That's not normal. S54 is a very responsive engine, it was built specifically NOT to act that way.
No, I think he was just referring to cold start and/or partial throttle (barely applying gas) situations, where the car does the bucking bronco almost. Which, I'm convinced is just the stock ECU's throttle mapping + drive-by-wire at work
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      09-13-2010, 11:51 PM   #15
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Quote:
Originally Posted by mfanatic325 View Post
No, I think he was just referring to cold start and/or partial throttle (barely applying gas) situations, where the car does the bucking bronco almost. Which, I'm convinced is just the stock ECU's throttle mapping + drive-by-wire at work
I would describe that as bucking then not rubber banding. And I don't think I've ever experienced that.
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      09-14-2010, 06:48 AM   #16
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Quote:
Originally Posted by O-cha View Post
I would describe that as bucking then not rubber banding. And I don't think I've ever experienced that.
^ Bucking is how I would describe it as well.
I have experienced it on occasion, usually in stop & go traffic & when I'm not really focused.
IMO, it's operator induced.

I find it's smoother (or I am) if I give the throttle a little blip before engaging the clutch.
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      09-14-2010, 06:57 AM   #17
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Quote:
Originally Posted by inTgr8r View Post
^ Bucking is how I would describe it as well.
I have experienced it on occasion, usually in stop & go traffic & when I'm not really focused.
IMO, it's operator induced.

I find it's smoother (or I am) if I give the throttle a little blip before engaging the clutch.
I think bucking is a fair description as well.

I don't doubt that some of it is the driver -- as I mentioned, I notice it happening less if I change my throttle input as well. The intent of my post was just to verify that this has been experienced by others, and that it's not just my car, and see if anyone might have some insight as to why it seems easier to induce this behavior in the M (e.g. if this is some characteristic of the flywheel in this car).
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      09-14-2010, 07:14 AM   #18
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IMO, I think it happens more just because you have more power & torque in the M.
When bucking starts it's self perpetuating because the lurching causes your foot pressure on the pedal to change.
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Last edited by inTgr8r; 09-14-2010 at 07:41 AM..
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      09-14-2010, 08:20 AM   #19
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I'd noticed this a couple of times in the past couple of weeks. Figured it was just me doing somethign wrong. The self-perpetuating really sucks too...can't help but do it. I just push the clutch back in and start over. Glad to know it's not just me...lol
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      09-15-2010, 01:40 AM   #20
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Quote:
Originally Posted by inTgr8r View Post
When bucking starts it's self perpetuating because the lurching causes your foot pressure on the pedal to change.
Bingo. Someone give this man a trophy =P
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      09-15-2010, 09:20 AM   #21
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Quote:
Originally Posted by inTgr8r View Post
IMO, I think it happens more just because you have more power & torque in the M.
When bucking starts it's self perpetuating because the lurching causes your foot pressure on the pedal to change.
You are probably sitting too far from the pedals.
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      09-15-2010, 09:30 AM   #22
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Quote:
Originally Posted by thekurgan View Post
You are probably sitting too far from the pedals.
I can see how that would make it easier to induce.

Not my situation though, I have lots of angle in my knees.
With me it's just once in a blue moon when I'm off thinking of something else;
e.g. if I get stuck in stop & go traffic.
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