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Steve Thomas BMW
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      01-10-2013, 07:59 PM   #1
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Shifting from R to D in AT while rolling..

Anyone do it consciously or unconsciously?

I picked up this dumb habit back in the high school days driving the ol 89 Camry and i catch myself still doing it in the f30. I wonder is it really harmful? My Camry went till 300k without a tranny failure and my 03 330ci has gone 150k with this habit on original trans and original oil. I shifted like this every day for years. Just curious...
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      01-10-2013, 08:34 PM   #2
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IMO it probably isn’t TERRIBLE for the car people do it all the time and its usually at a few MPH, but it certainly is probably better to be at a full stop just to be safe, why risk it.

Think about it this way, all the weight of your car rolling backwards at even a few MPH is still thousands of pounds weight..that the transmission will need to slow down, stop, then start moving forward.

If something ever did happen and you BMW was out of warranty, your looking at some big numbers.
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      01-10-2013, 08:40 PM   #3
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It's funny you're asking this, I was going to post the exact same question.

I've been doing this pretty much since I started driving. I do it with manuals and autos. Most people I know do it too. Obviously I'm talking of very slow speeds, like when pulling off of a parking spot, and I'm being very smooth.

However I've also wondered what's going on behind the scenes when I do this. Is there some form of fail-safe to prevent damage to the transmission when doing this? Surely this is something that has been thought about since most people drive this way.

Hopefully some mechanical-minded member of the forum will chime-in with some technical details...
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      01-10-2013, 09:26 PM   #4
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There's been fail safes to ignore such shifts at unsafe speeds for decades -- as early as the Crown Victoria.
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      01-10-2013, 09:49 PM   #5
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The tranny won't engage the next drive (forward to reverse or reverse to forward) until it detects that the car has reached a stop.
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      01-10-2013, 11:35 PM   #6
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The mechatronics will prevent it to engage gear until the speed is below certain threshold.
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      01-11-2013, 12:09 AM   #7
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The ActiveHybrid is exceptionally smooth when shifting between reverse and drive. It's probably the motor helping out.
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      01-11-2013, 12:27 AM   #8
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I do it all the time. Always unconsciously though. I don't think it's a big deal. My cars never have had a problem with it.
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      01-11-2013, 07:35 PM   #9
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An auto trans is comprised of a bunch of hydraulic clutches. It's completely decoupled unless you're spinning the motor fast enough to lock the torque converter. The act of "shifting" an automatic is redirecting the hydraulic fluid from one clutch pack to another.
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      01-14-2013, 02:18 AM   #10
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Have always done it. You have much better turns if you start steering the way you want to go while you are in the transition from reverse to forward.
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