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      12-23-2012, 04:39 PM   #1
SomeRandomer123's Avatar

Drives: F30 328i Luxury - Sport Auto
Join Date: May 2011
Location: Lancashire, North West England, UK

iTrader: (0)

Question 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!

Gone: 2006 BMW E60 520d SE 6MT
Gone: 2009 BMW E90-LCI 330d SE 6MT
Current: 2012 F30 328i Luxury 8AT
On Order: 2015 Audi A6 Avant Ultra, Black Edition (sorry!)
Appreciate 0