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Do 722.6 transmmissions make any noises as normal or are the completely silent?

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by chizzel89, Nov 12, 2012.

  1. chizzel89

    chizzel89 Senior Member

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    Your Mercedes:
    Mercedes-Benz C250 Turbodiesel Sport Auto. Estate. 1998. 180,000 mls
    If I manually select gears 1 or 2 (a bit in 3, though over 30mph road noise would drown it out anyway) on my gearbox, then I get a whine on the overrun/ under engine braking. Fairly high pitched. This happens in Drive too, but is most noticeable in the manual selections as the box cannot shift to neutral so the gears are constantly in mesh. I know that in a manual gearbox this is due to the back of the gear teeth not being machined or worn in in the same way as the side of the tooth normally in mesh when accelerating.

    Do other members 722.6 boxes make a similar sound when locked in a low gear or is mine clapped out?

    I did have a go in another C250TD with a higher mileage than mine and it made similar whiney noises on the overrun in the lower gears. Both his and my car have been doing it for ages (I think since before I got the car 20k miles ago) so if it is something letting go then it is taking its time?

    The other idea I had was maybe there's a worn thrust bearing, and when the load is transferred the other way down the geartrain on the overfun, it puts pressure on the worn bearing. But then why would the thrust bearing for the overrun direction be worn anyway, seeing as it is the one taking the brunt of acceleration which should surely wear first?
     
    Last edited: Nov 12, 2012
  2. CRH71

    CRH71 Senior Member

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    Your Mercedes:
    C250 TD
    Mine does exactly the same as yours under the same circumstance - 1999 C250TD, 169,000 miles.

    At first it bothered me, but as it only happens on the over-run and after giving it serious beans whilst locked in one of the lower gears, I've adjusted my driving style to suit.

    I suspect a change of fluid and filter would make the world of difference to our boxes.

    HTH
     
  3. television

    television Always remembered RIP

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    When quiet on the over run then usually the diff making the noise
     
  4. OP
    chizzel89

    chizzel89 Senior Member

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    Your Mercedes:
    Mercedes-Benz C250 Turbodiesel Sport Auto. Estate. 1998. 180,000 mls
    This is kind of a relief. I knew there would be others. How long has it been doing it and has it ever had a fluid change?

    I know there is a weak(ish) bushing in the trans which can fail, but I don't think it is associated with whining on the overrun for a long period of time. As far as I know once it starts wearing it fails quite quickly and totally destroys the transmission- this is the nature of plain bearings- once the oil films is broken up due to excessive play they fail quite quickly unlike roller bearings which can take much more abuse.

    Mine has had atleast one fluid change 30k miles ago, and possibly another before that as when the old fluid came out it wasn't too bad at all. Apparently hardly any debris in the filter or pan apart from some clutch material. No bronze. The fluid in there now is still nice and pink after 30k miles but Im thinking of changing it again as it is a cheap DIY job with the parts and fluid from ECP with the MECL025 discount code.

    Mine makes another noise, which I've been told by someone in the know is pump noise and nothing much to worry about. It presents as a barely distinguishable droning present in P and N. You only really notice it when you change from D to N. I have very keen hearing though, and almost everyone who gets in the car can't hear it!
     
  5. Steve@Avantgarde

    Steve@Avantgarde Forum Supporter Authorised Forum Supporter

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    C220CDI AMG Line Premium, SLR McLaren Roadster, SL55 & C32AMG
    Have to say mine has done 195k and is completely silent......or at least Ive not noticed anything like you are describing. But that can be down to 15 years of standing behind air guns etc....
     
    Last edited: Nov 12, 2012
  6. brandwooddixon

    brandwooddixon Senior Member

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    when the bushing starts to fail the gearbos will make a whining noise all of the time.
    A whine on overrun is probably the diff. the oil in which often gets forgotten about.
     
  7. stumo

    stumo Senior Member

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    Your Mercedes:
    ML270CDI 2002 facelift| Sprinter 316CDI 2003 LWB
    I know the exact sound you mean, and a few years ago when I posted the same question all I got back was "silence" so to speak, or the more common "its the diff" response. I can assure you it isn't the diff in my case.

    It seems to be extremely rare. My 722.6 in the ML270 does it, always has since I got it at 240kkm, 30kkm later it still does it. I have changed the filter and flushed in new 236.10 fluid when I got it, didn't make any difference. There was nothing untoward about the old fluid either.

    Only does it on overrun in second gear. All other gears, including first, are silent, and accel is silent (as far as I can tell) too. Like above it really bothered me for a while, but it seems to still be running just fine so meh.

    The 722.6 in my Sprinter 316 van doesn't do it, and it has 100 more kkm than the ML.

    EDIT: this is the thread I started way back then...
    http://forums.mercedesclub.org.uk/showthread.php?t=43379
     
    Last edited: Nov 13, 2012
  8. OP
    chizzel89

    chizzel89 Senior Member

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    Mercedes-Benz C250 Turbodiesel Sport Auto. Estate. 1998. 180,000 mls
    Yeah I'm fairly sure it's not the diff either. It sounds like its coming from the transmission. I should maybe get someone else to drive it whilst I sit in the back oneday. The oil was changed in the diff about 30k miles ago too, and I checked it recently and it was still level with the filler plug and crystal clear.

    I'm doing my best to find a donor vehicle ideally with less than 130k miles so I can have a spare trans ready and waiting should it fail, but it has been making these noises for pretty much the whole time I've had the car if not the whole time, and I've done a lot of miles in the 20 months Ive owned it.

    Stumo- I know what you mean about the responses. I have thankfully had some this time!
    I remember getting worried some time ago about a fairly loud whirring noise my engine makes when I rev it, and I posted on here and had no answers, but then started watching youtube videos and soon realised that all the OM605 Turbo engines make the same whirring/ whine when they rev up. God knows what it is that makes the noise, but it just seems to be a feature and I can't pin down where its coming from on the engine!
     
  9. OP
    chizzel89

    chizzel89 Senior Member

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    Your Mercedes:
    Mercedes-Benz C250 Turbodiesel Sport Auto. Estate. 1998. 180,000 mls
    I have the oppertunity of a donor car with 170k miles. It's a saloon with no towbar, so it won't have pulled much weight. Lots of service history. Gearbox oil and filter were changed about 6 months ago. So long as the box is quiet and works as it should would it be worth keeping as a spare? I have 2 post car lift and a transmission jack, so a trans change should be fairly straight forward?
     
  10. OP
    chizzel89

    chizzel89 Senior Member

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    Your Mercedes:
    Mercedes-Benz C250 Turbodiesel Sport Auto. Estate. 1998. 180,000 mls
    Just to finish this topic off, I now have three C250 TDs and they all make these noises.

    One has 180k miles and has had atleast two fluid and filter changes.
    Another has 175k miles and had a fluid & filter change 10k miles ago with 236.14 fluid.
    The most recently acquired one has done 118k miles (low mileage for age), has FSH, and when I checked the fluid it was not dirty at all and at the correct level.

    So, they all whine on the overrun in gears 1 and 2.
    They all make a faint droning when in P and N particularly when in S mode, though the low mileage one is barely audible. This leads me to believe that the noise is (pretty much benign) front pump noise.

    They all also make a kind of gear train spooling up noise when pulling away.

    And they all rarely do a harsh upshift (I think from 2-3) which thumps a bit and always happens after a period of coasting at low speed, then slowly bringing the engine revs back up to meet the cars speed.

    They also all seem to flare and hang slightly on upshifts on medium throttle.

    Atleast I can stop driving around with the music on all the time as I now know the noises are pretty standard. And if my gearbox does break, I have two excellent spare ones which I wouldn't hesitate to fit. Mercs are not silent, they have spinning whirring parts like other cars:mrgreen:
     

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