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      09-24-2011, 02:56 PM   #1
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5/6 gear noticeable engine compression jerk

Question, when cruising on the autobahn i noticed that when you let go the throttle quickly, the car gives a light jerk, something like a compression jerk in the lower gears (1/2). This doesn't happen if the throttle is let go smoothly.

Does this happen to anyone else? My 135 didn't do this other than 1/2. The mini I'm driving right now also doesn't have that effect. I'm wondering whether this has anything to do with the lighter flywheel etc.

Any input?
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      09-24-2011, 03:19 PM   #2
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Yes. All 1M's do this.
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      09-24-2011, 04:43 PM   #3
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My 1M does it also. Dealership tech said it was normal and related to the dual-mass flywheel and slack in the drive-train. Local BMW tuning shop confirmed the findings as well.

Below is the link to my original post about it...

http://www.1addicts.com/forums/showthread.php?t=565832

From what I can gather it is annoying but normal on these cars; you'll get used to it...

Enjoy your 1M!!!
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      09-24-2011, 04:48 PM   #4
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Yes mine does this as well...... And my freind's 325 ci as well
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      09-24-2011, 05:26 PM   #5
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Quote:
Originally Posted by miula View Post
My 1M does it also. Dealership tech said it was normal and related to the dual-mass flywheel and slack in the drive-train. Local BMW tuning shop confirmed the findings as well.

Below is the link to my original post about it...

http://www.1addicts.com/forums/showthread.php?t=565832

From what I can gather it is annoying but normal on these cars; you'll get used to it...

Enjoy your 1M!!!
I keep hearing about the dual-mass flywheel being responsible for everything from global warming to jerks, clutch slippage, etc. The dual mass flywheel is actually intended to dampen vibrations between engine and tranmission.

The jerk you feel is probably exacerbated by the LIGHTENED 1M flywheel that has a smaller mass and less inertia. So when you back off the throttle, the motor acts as a brake on the gearbox via the clutch/flywheel. A heavier flywheel has more rotational inertia due the the greater mass and it keeps spinning. That is one reason not every car has a lightened flywheel. It makes the car spool up faster BUT the opposite is true...it decelerates faster.

So what you have to do is learn how to shift. Most distributorless cars nowadays with fly-by-wire throttle have quicker response both on and off throttle. If you take your foot completely off the gas pedal during a shift, the motor has been temporarily shut down. Try keeping a slight bit of throttle during your shift and it should smooth out.

OR you can trade it for a Jaguar! : )
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      09-24-2011, 06:17 PM   #6
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Quote:
Originally Posted by nachob View Post
I keep hearing about the dual-mass flywheel being responsible for everything from global warming to jerks, clutch slippage, etc. The dual mass flywheel is actually intended to dampen vibrations between engine and tranmission.

The jerk you feel is probably exacerbated by the LIGHTENED 1M flywheel that has a smaller mass and less inertia. So when you back off the throttle, the motor acts as a brake on the gearbox via the clutch/flywheel. A heavier flywheel has more rotational inertia due the the greater mass and it keeps spinning. That is one reason not every car has a lightened flywheel. It makes the car spool up faster BUT the opposite is true...it decelerates faster.

So what you have to do is learn how to shift. Most distributorless cars nowadays with fly-by-wire throttle have quicker response both on and off throttle. If you take your foot completely off the gas pedal during a shift, the motor has been temporarily shut down. Try keeping a slight bit of throttle during your shift and it should smooth out.

OR you can trade it for a Jaguar! : )
A dual mass-flywheel has springs between the two masses in order to reduce vibration at idle and low speeds. When power is suddenly lost at higher speeds, the springs compress due to the difference in engine speed and road/differential speed. The abrupt expansion of these springs accounts for the jerk/jolt/compression felt. At least according to one of the mechanical engineers at BMW's prestigious M Division who stated the symptom is due to a combination of the dual-mass flywheel and the characteristics of the limited slip differential.

If the flywheel itself is the culprit or just transmitting it is not really important. Keeping the throttle applied slightly or very slowly easing off the gas helps reduce the jerk when shifting. However when slowing down, cruising or braking it is sometimes impossible to slowly ease of the throttle and I wouldn't recommend keeping your foot on the gas lightly while braking.

Personally I am extremely happy with my 1M and I don't really care for Jaguars. At the risk of sounding like a d@*#$%, I would say I am pretty good at shifting manual transmission cars and motorcycles and have been doing it successfully on and off the track for the last 10+ years. However I am available for private shifting lessons at the track of your choosing
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      09-24-2011, 07:48 PM   #7
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Quote:
Originally Posted by miula View Post
A dual mass-flywheel has springs between the two masses in order to reduce vibration at idle and low speeds. When power is suddenly lost at higher speeds, the springs compress due to the difference in engine speed and road/differential speed. The abrupt expansion of these springs accounts for the jerk/jolt/compression felt. At least according to one of the mechanical engineers at BMW's prestigious M Division who stated the symptom is due to a combination of the dual-mass flywheel and the characteristics of the limited slip differential.

If the flywheel itself is the culprit or just transmitting it is not really important. Keeping the throttle applied slightly or very slowly easing off the gas helps reduce the jerk when shifting. However when slowing down, cruising or braking it is sometimes impossible to slowly ease of the throttle and I wouldn't recommend keeping your foot on the gas lightly while braking.

Personally I am extremely happy with my 1M and I don't really care for Jaguars. At the risk of sounding like a d@*#$%, I would say I am pretty good at shifting manual transmission cars and motorcycles and have been doing it successfully on and off the track for the last 10+ years. However I am available for private shifting lessons at the track of your choosing
FYI, The Jaguar bit was because another member recently traded 1M because it was too stiff and loud for him so he said he wants to buy a Jaguar instead. I am not complaining about the 1M, I love it just as it is and not a Jaguar fan myself. Just wanted to clarify that part!
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      09-25-2011, 01:33 AM   #8
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Quote:
Originally Posted by nachob View Post
FYI, The Jaguar bit was because another member recently traded 1M because it was too stiff and loud for him so he said he wants to buy a Jaguar instead. I am not complaining about the 1M, I love it just as it is and not a Jaguar fan myself. Just wanted to clarify that part!
No worries... I assumed we were both joking around while trying to make our point
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      09-25-2011, 09:26 AM   #9
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Thanks for the replies guys. Figured it had something to do with the light flywheel and the LSD.
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      09-26-2011, 04:48 AM   #10
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Thanks guy, i've also noticed it on my 1M and was a little bit worried : but it's okay
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      09-26-2011, 08:49 AM   #11
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Anybody making a single mass LW flywheel yet? Also, anyone happen two know the weight of the stock unit?
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