Mercedes SLK World banner

1 - 9 of 9 Posts

·
Banned
Joined
·
992 Posts
Discussion Starter #1
Before the 'MCT' was introduced, what's the difference between the 7G transmission with 'AMG Speedshift' and all the other 7G units fitted to 171s?

Wikigoogle couldn't really satisfy my curiosity.
 

·
Administrator - Founding Member since 2006
Joined
·
94,091 Posts
wiki didn't satisfy?

AMG SpeedShift MCT[edit]

Mercedes-AMG developed the 7-speed MCT "Multi Clutch Technology" planetary semi-automatic transmission.
The MCT transmission is essentially the 7G-Tronic automatic transmission without a torque converter. Instead of a torque converter, it uses a compact wet startup clutch to launch the car from a stop, and also supports computer-controlled double declutching. The MCT (Multi-Clutch Technology) acronym refers to a planetary (automatic) transmission’s multiple clutches and bands for each gear.[4]
The MCT is fitted with four drive modes: “C” (Comfort), “S” (Sport), “S+” (Sport plus) and “M” (Manual) and boasts 100 millisecond shifts in "M" and "S+" modes. MCT-equipped cars are also fitted with the new AMG DRIVE UNIT with innovative Race Start function. The AMG DRIVE UNIT is the central control unit for the AMG SPEEDSHIFT MCT 7-speed sports transmission and all driving dynamics functions. The driver can change gears either using the selector lever, or by nudging the steering-wheel shift paddles. The new Race start Function is a launch control system which enables the driver to call on maximum acceleration, while ensuring optimum traction of the driven wheels.

Maybe you need new Burger King's Satisfries!

 

·
Banned
Joined
·
992 Posts
Discussion Starter #4
^^^^^^^^^^^^^^


Before the 'MCT' was introduced, what's the difference between the 7G transmission with 'AMG Speedshift' and all the other 7G units fitted to 171s?

Wikigoogle couldn't really satisfy my curiosity.
 

·
Premium Member
Joined
·
771 Posts
Before the 'MCT' was introduced, what's the difference between the 7G transmission with 'AMG Speedshift' and all the other 7G units fitted to 171s?
Not sure if this helps your quest:

http://www.roadandtrack.com/car-reviews/first-drives/mercedes-benz-slk55-amg

AMG's V-8 develops 355 bhp and a hefty 376 lb.-ft. of torque and drives the rear wheels through M-B's new 7-speed automatic transmission, modified with AMG's SpeedShift fully adaptive program. Not only does it include Comfort and Sport modes, but also a Manual mode that can be operated sequentially either by moving the gear selector to the right or left, or by fingertip paddles behind the steering wheel (right for upshifts, left for downshifts).

AMG modifications to the transmission program include torque-converter lockup from 1st gear on, so that, once the car is running with no converter "cushion," throttle response is as quick throughout the range as with a manual transmission. Switching from Comfort to Sport not only raises the shift-up and shift-down speeds, but quickens the shift itself by up to 35 percent at the cost of only a slight loss of smoothness. A fairly hard application of the brakes also makes the transmission shift down into the appropriate gear, just as a driver would do with a manual transmission before negotiating a corner. Even in the automatic mode, the driver can manually select the gear of his choice.

The third mode is Manual, without any electronically governed intervention. There is no automatic downshift at low speed or an automatic upshift when the engine reaches its redline, and the kick-down remains inoperative.
Fwiw, the R172 slk 55 amg doesn't have MCT either:

http://www.mercedes-amg.com/slk55.php

AMG SPEEDSHIFT PLUS 7G-TRONIC

Power is transferred to the rear wheels by means of the AMG SPEEDSHIFT PLUS 7G-TRONIC automatic transmission which features three transmission modes: "Controlled Efficiency" (C), Sport (S) and Manual (M). The automatic double-declutching function when downshifting as well as the brief, precisely defined interruption of ignition and injection when upshifting under full load shorten shifting times and increase emotional appeal when adopting a sporty driving style. A double turbine torsional damper with centrifugal pendulum which adapts to engine speed helps to minimise vibrations in four-cylinder operation and enhances the impression of comfort experienced by the vehicle occupants.
 

·
Banned
Joined
·
992 Posts
Discussion Starter #7
^^^

Thanks random, best explanation I've seen so far.

The third mode is Manual, without any electronically governed intervention. There is no automatic downshift at low speed or an automatic upshift when the engine reaches its redline, and the kick-down remains inoperative.

I'm going to have to try this out. It implies you can hold a high gear and use the engine's torque, but I'm pretty sure that's not the case. That's my only real criticism of the 7G - it's desire to downshift at anything more than very light throttle. The improved shift times explains why I haven't found the transmission slow enough to warrant even considering a manual.

BTW, I've always wanted a 'double turbine torsional damper with centrifugal pendulum', so now I'm jealous.:D
 

·
Premium Member
Joined
·
771 Posts
There is no automatic downshift at low speed
that doesn't sound right to me either as it would lead to stalling. It's certainly not the case with the R172 version as that downshifts automatically in manual mode when the rpm gets into stall territory.

it's desire to downshift at anything more than very light throttle
same in the r172 too - neither manual nor sport auto fully hit the spot for me, but limiting the high gear in sport auto is the mode I've settled on. At least using that stops it hunting to 6th/7th on light throttle and then dropping down to 4th when the mere thought of pressing the throttle flashes across my mind.

In essence, I pretty much use the range limiting as a manual control over the way it works - at least it stops it hitting redline as much as it was in manual due to the slow reaction to paddle pulls.

In sport auto mode, it knows I've allowed it to go to a higher gear, but it still seems to hold onto the current gear for long enough to mean it isn't short shifting.

BTW, I've always wanted a 'double turbine torsional damper with centrifugal pendulum', so now I'm jealous.
:)
 

·
Banned
Joined
·
992 Posts
Discussion Starter #9
So I played around with 'M' for a while today. Basically, it won't change up automatically (obviously), but it will progressively change down as the revs drop to abt 1200 rpm. In effect, it's quite a nice driving technique just changing up tapping the shifter or the button to get to the highest gear possible, as soon as possible, and then giving it a lot of foot to feel the torque of the engine. The only downside to this is that you 'might' ahem, find yourself doing 80 in a 40 due to the quiet, effortless tug from the V8. Also (I had read this), it starts in first in both forward and reverse, while in 'M'or 'S' which means there's a lot more creep at tickover than when in 'C'.
 
1 - 9 of 9 Posts
Top