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Originally Posted by J08M3
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I understand the actual shift if very fast, but from what I read (since I haven't gotten to drive one yet) there is a slight lag between when you hit the paddle and the shift happens. Why is there a lag and how bad is it?
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You really need to drive an M-DCT car to get a true feel for the “delay”. Swamp was kind enough to give me an introduction. Then we purchased on July 2 and traded our 1995 E36 M3……life just isn’t the same.
My “butt meter” says that damm! this is consistently the fastest shifting production street transmission on the planet. Then my understanding of power train takes over and I know that the shift didn’t happen instantly just like it doesn’t in a manual transmission car.
Manual Transmission:
Driver decides it’s time to shift
Takes hand off steering wheel to grab shifter
Pushes clutch in (even if you don’t use the clutch it still takes time to pull the lever)
Moves shift lever
Releases the clutch pedal
Returns hand to steering wheel.
M-DCT:
Driver decides it’s time to shift
Pulls paddle with fingers
The steering column switch cluster sends a signal to the M-DCT electronics (attached to the passenger side of the transmission.
The decision on how fast to shift is determined by data (load, RPM, rate of throttle movement, temp, etc….) from the DME –Digital Engine Electronics through the PT-CAN buss connected to the M-DCT electronics.
Electronic signals are sent to the clutch and shift rail control valves.
Hydraulic transmission fluid pressure moves the shift rail to select the gear
(Note: with the DCT very often the gear has been pre-selected because the software makes a decision about what the driver/vehicle will need.
The
active clutch hydraulic pressure is dumped and the clutch releases with spring pressure. The
selected clutch is engaged by using hydraulic pressure. This timing is critical because both clutches
CAN NOT be engaged at the
same time!
BAM another amazing shift
The M-DCT “delay” is like many other electro-mechanical devices….you push the keys and it takes a while for the letters to appear on the screen. As long as I push the right key I get what I hoped for.
I like my M-DCT M3 because of the automatic mode and manual mode. This transmission is also one of the smoothest shifting automatic transmissions I have experienced and my wife can drive it if needed. You will see many more manufacturers beginning to use DCT’s to replace traditional automatic transmissions.
As a point of reference I have taught college level automatic and manual transmission classes for 32 years. From 1970-72 I drove an SS/DA 1970 Dodge Challenger 426 Hemi (manual valve body automatic) 10.50s @ 130 mph and a street 340 cid 1968 Dodge Dart (also an automatic) that ran 13.13 @ 110 mph.