05-26-2013, 08:29 PM | #1 |
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205 8AT transmission "launch mode"
Yesterday I was trying to time my car's acceleration, and I noticed something rather interesting.
My car has the regular 205 8AT transmission (not the 2TB 8AT sport transmission), as I'm not even sure you can get the sport transmission for the 118i, but anyway, when I launched with the DSC-OFF mode, after holding the brakes and revving up to 2500-3000 rpm, the car would upshift dramatically quicker than normal. The car doesn't have a proper launch control, especially because if you hold the brakes for too long, the wheels will start smoking the tires before the car actually moves, but at least the gearbox operates much more aggressively, about as quickly as DSG. Has anyone else noticed this? I'll try to make a video about it later this week. I was also wondering if this has been documented somewhere. |
05-27-2013, 05:30 PM | #2 | |
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I think we dont have launch mode. But there is an update on the US verion of the ZF transmission that said it would get Launch mode. But no one knows if its just an software update or a hardware yet. You could be on something though, as no one has said anything yet. When you rev it, do you floor it and the revs hold at 2500-3000, or so you manually keep it between that rpm? Try making a video by doing your procedures and one video by just accelerating from a stand still without brake pressed. |
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05-27-2013, 06:32 PM | #3 |
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I am not 100% sure, it should be a programmed control in the EMC, perhaps they use a different fluid control modulator in the new ZF box, however I would be wary of the potential damage that could be caused to your box if you were to do the 'holding the brakes and revving up to 2500-3000 rpm' too often.
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05-27-2013, 06:56 PM | #4 | ||
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05-28-2013, 02:00 AM | #5 | |
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Sounds like an excellent way
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05-28-2013, 06:20 AM | #6 |
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When you press the brake pedal and let the wheels (almost) spin
you create an extreme amount of stress on all the drivetrain components. Especially the first gear, which is a very small gear with a small number of teeth. When these teeth start to slip, or even worse when they break, you will get a avalanche of problems. My teacher 'drivetrain and gearboxes' does warranty and failure expertises for BMW, Audi and Mercedes. He claims that car manufacturers will not warranty parts when 'abused'. Last edited by Callthecops; 05-28-2013 at 08:02 AM.. |
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05-31-2013, 01:00 AM | #7 | |
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05-31-2013, 07:44 AM | #8 | ||
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Torque converter units are design to cope with slippage (that's what prevents the engine from turning off when you come to a complete stop) and each unit has a designated "stall rpm" which is the maximum the gearbox can cope before the first gear is completely engaged. Stall here obviously doesn't mean that the engine shuts down, but rather means that rpms will no longer rise. Holding the brakes and accelerating is also a test to verify problems with the gearbox, in case the stall is reached before or after the designated rpm. There's no risk to the gear cogs themselves because they're only completely attached after the lockup is engaged. And although this new 8hp from ZF does have an aggressive torque converter lockup already on first gear, it is electronically managed, and does not engage if the car's not running. In any case, the possibility of damage here comes from overheating the gearbox, which would prevent the fluid from avoiding tear and wear of the individual components, namely the clutch packs that switch gears. Therefore it is important not to repeat this too often, not to hold it for too long (or rev too high), and to give time for the gearbox to cooldown properly before attempting it again. That is why holding burnouts can quickly damage automatic gearboxes. Let's also keep in mind that this unit is the very same that equips the m135i and other diesel engines, so factory default it is engineered to take a whole lot more torque than the 118i can ever hope to produce. Quote:
To everyone else, I appreciate your concern that I might be doing something harmful to my car. And even though I am adamant that its not the case, once again I'd like to point out that I do not launch my car like this as a habit, it was a one time event in a closed road, and I gave my car long intervals of regular driving and cooldown between each run. I'll try to do it again if I get the chance so you guys can see the shifting behavior I was talking about when I started this post! Last edited by rpagianotto; 05-31-2013 at 09:02 AM.. |
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05-31-2013, 09:16 AM | #9 |
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Edmunds seem to have come along something similar while reviewing an f30 328i without the sport transmission:
http://www.edmunds.com/bmw/3-series/...ison-test.html Test Driver Ratings & Comments Acceleration comments: Seriously strong revver. In Sport and DS modes, while overlapping throttle and brake to bring revs to 2,000 rpm, the tranny went into a quick-shift mode, banging off lightning-quick shifts for the 1-2 and 2-3, then shifted normally for the 3-4. This greatly improved times. Manual shifting is via console lever (push forward for downshifts). Blips throttle on downshifts, does not hold gears to rev limiter. |
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