7G auto box

Discussion in 'Engine' started by davycaslad, Aug 7, 2008.

  1. davycaslad

    davycaslad Active Member

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    Hi

    I have now got my new c320 diesel sport i just wanted to know does it learn your driving style over time i have 569 miles on the clock but i get the feeling the car is hunting for gears always, anyone else had this ?
     
  2. se97mlm

    se97mlm Hardcore MB Enthusiast

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    Not sure about the gearbox, but the engine ECU rates the driver all the time, to determine if you're a comfort driver or a dynamic driver. It collects data on pedal position, pedal acceleration, and vehicle lateral acceleration. You are then rated seperately for how you like to drive in corners, and how much gas you like to give. THe data is not saved, it's just used to determine how sensitive your throttle pedal should be.

    Matt
     
  3. Dieselman

    Dieselman Banned

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    Isn't gear hunting a critisism of the 7G gearbox. Too many ratios, especially for a diesel.
     
  4. st4

    st4 Banned

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    I've heard this, and TBH its common sense. Unless a car has very high top speed (think 200mph+) and a very narrow power band (think BMW M5 V10 engine) then 7 cogs might be an idea but for a car with a top speed of c. 150mph 6 is plenty and 5 easily sufficient.

    A high performance diesel car (think 330d or E320cdi) doesn't need 7 gears as it will not be doing 200mph and it has a wide power band. 5 speeds are fine, any more and it will go looking.
     
  5. whitenemesis

    whitenemesis MB Club Veteran

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    Is there a difference between hunting and swapping?

    I mean the 7G has more gears to choose from so as the speeds and loads vary slightly a different range is identified as optimal and a change is made.

    Hunting implies the box doesn't know which range is optimal and keeps changing between ratios.

    Semantics perhaps but one (hunting) would be a fault, the other would be making optimal use of the available ratios, even if the number are excessive, it wouldn't be faulty
     
  6. oldcro

    oldcro Hardcore MB Enthusiast

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    My experience of the 7 speed gearbox is that it is one of the best, as the only way I know what gear I'm in is to check speed against revs. Most gear changes are only realised when the revs drop.

    I'm comparing it with Audi, BMW and Lexus which comes a close second, against my normal driving state so others may feel different if a more sporty drive is preferred.
     
  7. st4

    st4 Banned

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    All very true, but due to the excessive number of forward gears is swaps cogs to find the optimal gear (for that gear box), and due to the increased number of cogs, it swaps more than a car with less cogs.

    This would give the feeling of hunting. I know the V10 Toureg with 6 forward speeds was thought to be doing this, with such massive torque it simply needed less gears. I found this with a 6 speed auto BMW, it would change gear in an uphill corner just to bring engine speed up by 600 or so rpm, when what I really wanted to do was just use the low down grunt.

    My view is that when I change my car, I'll go for the w204 220 to avoid the 7 speed box, and I think it shows that MB have very little faith in their engines and power bands that they need such a box.
     
  8. whitenemesis

    whitenemesis MB Club Veteran

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    I agree with you *** a torquey engine needs less gears to still cope and perhaps the gains by having a 7 speed box are too marginal to really warrant it.

    Don't MB offer the 5G as a no cost option on its new cars?
     
  9. st4

    st4 Banned

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    We can but hope...

    As for lexus 8 spd job :devil:

    Off thread slightly but when I was learning to drive my instructor had a 964 Porka, and it had 5 speeds. The 993 that superseded it has 6 speeds. He preferred the 5 speed car due to the torque of the engine as it didn't need 6 speeds, and he said Porsche did this for marketing as rivals were using 6 speed boxes. In other words the marketing boys damaged the integrity of the car.

    A lot of people think more is better, and a lot of the time that just isn't true.
     
  10. whitenemesis

    whitenemesis MB Club Veteran

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    As I keep telling Mrs WN......
     
  11. sylvester

    sylvester Member

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    Congratulations, hope your enjoying it.
    Are you driving in comfort or sport when you get the impression that the box is hunting between gears or does it feel the same in both modes ?
     
  12. Colin_b

    Colin_b Hardcore MB Enthusiast

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    I had a car with a 3 speed box. 5.7l V8, so the torque kind of masked the lack of gears by sacrificing fuel.

    A 7 speed auto box keeps the engine at the right place in its rev range (mostly) based on your choice of comfort or speed. It will change down 2 or more gears if you want the performance, or not if gentle is what you need.

    Its progress. You neither really know if you are in 5th, 6th or 7th most of the time, unless you look, nor care. (assuming the system works properly, which my merc, at least, it seems to)

    My 5.7l car did 6mpg. My merc does 28mpg, and is faster, more responsive and altogether much, much nicer to drive. More gears in the box, a smarter fuelling system and ECU. Progress:)
     
  13. Dieter

    Dieter Hardcore MB Enthusiast

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    Hi,

    My 7-speed box (ML) doesn't 'hunt'....it just changes up and down 'seemlessly' i.e. I hardly notice gear changes :)

    Only problem is that when travelling slowly (jams etc.) it does occasionally 'jerk'...but this is well documented....though there are supposed to be software updates to address this problem.

    My experience is in agreement with Colin's.

    Dave...you ought to get it checked out....if it really is that bad.

    Cheers,
     
  14. davidjpowell

    davidjpowell Hardcore MB Enthusiast

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    Hi - it does adapt over time. Every time they reset my gearbox ECU I have to go through a period of the gearbox not being where I want it to be, but it does learn.

    David
     
  15. ddentrec

    ddentrec Hardcore MB Enthusiast

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    My C180K - 5spd auto 'box- has seamless changes too.

    Eh? My C180K is seamless when in traffic. No jerks or flare or anything.

    So is MB's transmission development team so bad that they never noticed this (or more likely they did but launched it anyway to meet schedule)? Jeez. As I have said before on this forum never buy the first release of anything new.
     
  16. C43AMG

    C43AMG MB Club Veteran

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    I get the occasional jerk in traffic with the SClass. I have spoken to the service manager at Brooklands and there is a software program so that will be done when it goes in for it's first service, told him i was very disappointed.
     
  17. crockers

    crockers MB Club Veteran

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    Can't say I have ever felt it hunt... it seems totally seemless to me..

    I would say before knocking it -- try it...

    If your car is "hunting" then something is wrong and I would get it addressed...
     
  18. st4

    st4 Banned

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    What your really saying is that you'd really be okay with 5speeds.
     
  19. oldcro

    oldcro Hardcore MB Enthusiast

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    How many of those who are knocking the 7 speed box actually have one?
     
  20. Dieter

    Dieter Hardcore MB Enthusiast

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    Hi,

    Some "quotes" re 7-G tronic auto gearbox i.e. as to why MB bothered to design and build it at all (cos some of you know better :eek: )

    "The company claims that the 7G-Tronic can save up to 0.6 litres of fuel per 100 kilometers (depending on the car) and has shorter acceleration times and quicker intermediate sprints than the outgoing 5-speed automatic transmission".

    "The transmission can skip gears when downshifting, allowing for quicker acceleration. It also has a lockup torque converter on all seven gears, allowing better transmission of torque for improved acceleration. The transmission's case is made of magnesium, a first for the industry, to save weight."

    I beleve the low speed jerkiness may result from lockup of torque converter (see above) ?

    Overall I still get same mpg from 320 CDi as I got from 270 CDi even though the 320 has some 57 MORE BHP.

    There are plenty of 4-speed autos out there if you want one :eek:

    I agree wholeheartedly with "OldCro".

    Cheers,
     
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