W211/ 7g Tronic - Downshifting & Braking Effect- Reluctance Rings ABS

Discussion in 'Engine' started by mystic.bertie, Sep 28, 2016.

  1. mystic.bertie

    mystic.bertie Active Member

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    I thought i would start a new thread to see if anyone has cured this problem with the ABS reluctance rings. My 7g gearbox was serviced and software updated a few weeks ago so its not that.

    When driving around town, if i take my foot off to coast and slow down, i get a light braking effect when it down-shifts at 30mph then 20mph then 10mph, the lower the gear the more obvious it is.

    I took it to G-services in Coventry today, he is the indy who did my gearbox service. He connected the diagnostics and he found no errors on the gearbox. He checked another control module and said there was dodgy reading from the rear wheel sensors, he said the abs rings need replaced and he thinks that is what is causing my problem.

    So has anyone else had this problem and found the ABS rings were to blame, i know MB want to sell you a full drive shaft but aftermarket ABS rings can be fitted. I was quoted £220 for both sides.

    I have also read on other posts, people getting the gearbox software reset and software updates and it did not cure the problem. Is this the answer?
     
  2. whitenemesis

    whitenemesis MB Club Veteran

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    Isn't this just the normal effect of engine braking?
     
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    mystic.bertie

    mystic.bertie Active Member

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    It should not be that noticable in my opinion, it should coast smoothly.
     
  4. Trickythemerc

    Trickythemerc MB Enthusiast

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    I would agree with Whitenemesis on that one.
     
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    mystic.bertie

    mystic.bertie Active Member

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    here is an example from someone elses thread

    The 7g+ in my 4 month old c220cdi is good most of the time but in E mode the jolt when changing from 2nd to 1st when slowing to a stop is both frustrating and annoying. Also jolts when going into reverse.
    Been back to mb and told all is fine and all latest software loaded.
    Doesn't sound like much but takes the edge off what is otherwise a great car.

    another

    The 7g in this 220CDi is super slick.
    I cannot actually feel it shift in lower gears at light loading.
    There is a perceptible 'jolt' on some downshifts when decelerating hard.
    Not sure yet where as its not always repeatable.

    more

    http://www.mbclub.co.uk/forums/engine/98963-c63-amg-7gtronic-plus-downshifting-into-1st.html
     
    Last edited: Sep 28, 2016
  6. whitenemesis

    whitenemesis MB Club Veteran

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    The 'jolt' is a well documented characteristic of the 7g box. Usually sorted with a software update.

    I don't see the connection with what you are describing
     
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    mystic.bertie

    mystic.bertie Active Member

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    Maybe what they are describing is different. I have had the software update and the oil changed, gear changes are better but this braking effect when downshifting is worse, i dont know if it a coincidence or if it is those ABS rings.

    My car does not pull away in 2nd gear in C mode and warm, also there is no difference between gear changes in S or C. Light footed at 1600 rpm and 4000 rpm when flooring it.
     
  8. KeithJG

    KeithJG Active Member

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    All I will add is that I agree with those that have said that the feeling of retardation that you are getting when slowing down is completely normal for a 7g in good order.

    Mine did not do this and it drove ok with no error codes for over a year before it stopped and clunked into gear afterwards upon restarting, then it had error codes.

    After having a brand new hydroelectric plate fitted it now drives as it should and I get a very subtle dropping in gears when braking on slowing up.

    Looking at it logically if the box is dropping gears on slow up it would give a braking effect as the revs are on idle!.....or a closed throttle with the fuel shut off.

    Old auto's don'the give a braking effect on slow down or going downhill....one has to choose the L for lower gears, if you don't it is like freewheeling or coasting and when applying the throttle again the revs catch up.
     
    Last edited: Sep 28, 2016
  9. PobodY

    PobodY MB Enthusiast

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    I can feel the drag when engine braking in low gears; that's what it's supposed to do because it's locking the torque convertor (as opposed to older non-locking auto boxes, that didn't lock). - I don't notice anything when it's doing its own thing without my intevention.

    To be honest it's not something I use very often; I just use the foot brake. - With ABS etc there isn't a great chance that I'll lock the wheels.

    If yours is jerking and dragging whilst working automatically, I think there's a fault. If it does it when you manually select gears, that's probably normal operation.
     
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    mystic.bertie

    mystic.bertie Active Member

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    My car does this in auto mode, i dont tend to use the gears manually.

    Where im staying just now, there is 2 sets of speed humps just along the road. If i take my foot off, it feels terrible, its like someone is braking for me as i am trying to coast over the speed hump slowly. Its much better if i roll over them in neutral. It really feels rubbish. :confused:
     
  11. streethawk

    streethawk MB Enthusiast

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    Mine sometimes if not most when cold and slowing to a stop will clunk into first. It makes no noise it just the only way I can describe it. I also feel engine braking more when cold. When warm it still slows as you would with gears on a manual which as far as iam concerned is normal. Try putting it in manual and using it like a manual to slow down! It work just like a manual. I think your's is normal by the sounds of it.
     
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    mystic.bertie

    mystic.bertie Active Member

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    I will try manual again, i tried this already but it does not work trying to keep it in second because as soon as i hit 10mph it auto changes down by itself to 1st, thats the problem with manual mode, i cant hold it in a higher gear, it auto changes down depending on speed.
     
  13. mbishton

    mbishton New Member

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    2006 CLS 320Cdi
    Hi all, did anyone get a definitive answer on this as my 06 CLS seems to be doing this, very noticeably some days and then freewheels really well other days!!

    Thanks!
     

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