12-23-2012, 03:39 PM | #1 |
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8AT - Reverse Gear
Noticed something recently! Was hoping other Automatic or Sport Automatic Transmission owners could chime in too. Mine's a Sport Auto, although I think the standard will also do the same.
The other week, I was travelling down a narrow lane and an oncoming car approached, so I stopped and engaged R to go to a passing place 300-400m back. Being a confident reverser (not to come across big headed!), I got a move on and briskly accelerated to about 10-15mph. As I was accelerating there was a bump as if the car had changed gear in M/S mode (where the changes are fully sharpened up like a Double Clutch Transmission) and the revs dropped, although I wasn't studying the needle. That got me thinking then, do we have multiple reverse gears in our 8AT's?! But then I was also arguing to myself that the bump was a bit too pronounced for Comfort mode, and obviously, you can't engage R in M/S or DS mode. So today, I went dropping off Christmas presents to the relatives and again, the road is only wide enough in this section for one car and as Sod's Law dictates, another car approaches. A Renault Scenic on this occasion! Seeing the panic in the driver's face at the prospect of reversing, I thought I'd just bloody get on with it. The difference this time being, I was reversing up a VERY steep hill, not the flat as before! So much so, I was worried about breaking traction being RWD, but thankfully the 255's had plenty of grip! So, I went from D to R and stepped on it. This time however, I monitored the revs more closely, and as I began to travel backwards they shot up to 2000rpm and stayed there as I was accelerating until there was a bump and they dived down to approx 1200rpm. Following this event, I thought again! Torque converter. With this car being my first automatic, and one of the finest ever to be put into a car, I've gotten used to 1st gear being engaged without any noticeable slip from the torque converter - it's just like fully engaging the clutch as you pull away in a manual transmission. So, this is where I need your evaluation; my conclusion: When accelerating in R, the torque converter doesn't fully lock up until about 5-8mph and when it does, it does so sharply, giving the bump sensation I was experiencing. And R is only one gear. Seems like a long gear though if it's doing ~ 1200rpm at over 10mph. Now I need your thoughts: why is this? Why doesn't it act like 1st gear does, giving you complete connection? And Merry Christmas to you all!
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12-23-2012, 04:38 PM | #3 | |
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12-23-2012, 09:42 PM | #4 |
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The gearbox is only designed to handle max 3,500rpm in reverse gear, it may have sth to do with it.
U seem to like to experiment ur car to the limit in ways ppl have never thought of. |
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12-24-2012, 04:03 AM | #6 | |
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12-24-2012, 05:43 AM | #7 |
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Ahh is that right? Interesting! People were also saying that the car rev limits itself to 3500rpm in N or P, but I'm not fussed on trying that because it's not a problem I'm ever going to encounter in a real world situation, plus I don't like an unloaded engine to achieve a high engine speed.
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12-24-2012, 05:48 AM | #8 | |
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12-24-2012, 01:06 PM | #9 |
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I used manual for years and 320d is my first automatic too in this time i never released the clutch fully for reversing in manual transmission, always halfclutch. Bimmer is doing that in a way i think, when the limit reaches gearbox fully engages and that is your bump??
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