722.6 Gearbox Change Points

Discussion in 'General Discussion' started by E55BOF, Jun 12, 2019.

  1. E55BOF

    E55BOF MB Club Veteran

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    I've posted this in the Oily Bits forum, about the 722.6 five-speed transmission in my '03 49K-miler ML320:

    "Once in fifth gear, the transmission will not downshift automatically over about 40 mph even at full throttle, and the kickdown does not seem to work at all. Using the Tiptronic for manual shifts everything is normal, so I doubt it is a gearbox mechanical problem."

    I'm now used to the much more responsive seven-speed boxes in the much more powerful AMGs, and I know the 722.6 'box in the E55Ks had much more performance-orientated shift points anyway.

    The kickdown switch I can and will fix or adjust. However, thinking about it, the 'box may in fact be changing gears exactly as it is programmed to. Pootling around town, it shifts up and down perfectly. I can't find a single mention of my 'problem 'anywhere on the internet.

    ISTR that on at least one of my W211s (can't recall exactly which one; there have been so many...) I found the gearbox surprisingly unwilling to change down on the motorway unless I used either Tiptronic or kickdown. The ML is a pretty sedate car, and getting into top gear early and staying there might well be exactly what MB envisaged most of its buyers would prefer.

    Is there anyone else on here with an M112-engine/722.6 'box car that would comment on their gearchange downshift points?
     
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  3. DSM10000

    DSM10000 MB Club Veteran

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    I had the same engine / gearbox combination in my (much lighter) W203 C320 and found the gearbox whilst a little slow to respond unless given a swift and firm prod on the throttle but would happily kick down from 5th at motorway speeds. 40mph was usually the lowest speed that 5th gear would engage on the flat .
     
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  4. OP
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    E55BOF

    E55BOF MB Club Veteran

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    That makes sense and fits the car's behaviour. I usually just roll on the throttle to the stop; the ML is a stately old bus, and that seems most appropriate. I read on another website a little earlier that if you open the throttle quickly the box is more likely to change down, so I'll give that a go and see what happens. There's no kickdown of course, but I can't adjust the kickdown switch at the moment because it's pouring with rain.

    Yesterday I thought I'd bought a pup; I think now that I probably haven't.
     
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  5. OP
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    E55BOF

    E55BOF MB Club Veteran

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    Gave it a go; nothing different happened with snapping open the throttle. If I hold it in the gears with Tiptronic, it seems to rev OK, but from a full-throttle standing start, letting the box run up through the gears automatically, it does not go beyond about 4000 to 4250 revs before changing up. There's something not right, but what? Could that be an effect of the kickdown switch not being depressed at full throttle?
     
  6. OP
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    E55BOF

    E55BOF MB Club Veteran

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    The kickdown switch is definitely clicking at full throttle. Since I have the TCM switch readout "S16/6 (Kickdown Switch) Not Operating", that would imply that either the switch itself is faulty, or there's a wiring fault. Time to get the circuit tester out and check the switch, I think. I do hope that's all it is; if not, I have bought a pup, and the question will be, how much will the vet's bill be?
     
  7. OP
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    E55BOF

    E55BOF MB Club Veteran

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    Cleared all the codes, took it for a run with the iCarsoft in TCM datastream mode. Full throttle, felt the switch click, message: 'S16/6 Kickdown Switch Not Operating'. No fault codes recorded.

    I've ordered a new switch, and that should sort it out (he said hopefully...).
     
  8. OP
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    E55BOF

    E55BOF MB Club Veteran

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    New switch fitted, and working - much more positive click than the old one - but the transmission still seems to be very keen to stay in top, or fourth at best, at any motorway speed, even when I use kickdown going up a fairly steep incline. It will drop down to third fine if I use Tiptronic, so I'm assuming that MB did consider that ML buyers wouldn't be in all that much of a hurry, and it's doing what it is programmed to do. It may change as the box adapts to my driving style, but I can live with it as it is anyway.
     
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  9. AltonAnt

    AltonAnt Hardcore MB Enthusiast

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    Have you reset the gearbox adaptions?
     
  10. OP
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    E55BOF

    E55BOF MB Club Veteran

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    I haven't yet, because as I understand it, the gearbox will, over time, adapt itself to my driving and eventually end up fully-adapted anyway. I'll give it a go, though, and see. I 'll be surprised if a reset can really make the huge difference that is needed in my case, but I've nothing to lose.
     
  11. AltonAnt

    AltonAnt Hardcore MB Enthusiast

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    I don't think it will make a great difference but for the 30 secs it takes you'll at least know you are starting from fresh.
    The gearbox service made the biggest difference to me as I have no record of the fluid or filter having been changed.
    So at 80k it has made the changes that much more snappy. There was surprisingly no issues whatsoever with the car before however.
     
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  12. kid-jensen

    kid-jensen Hardcore MB Enthusiast

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    Those change point revs you mentioned above seem perfect to me, there's not a lot of power above those revs, so time to change-up.

    The reverse problem (holding on to the gears too long) is a far more common fault..
     
  13. OP
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    E55BOF

    E55BOF MB Club Veteran

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    The change-up points would be fine for a diesel, but a W163 320 has a petrol engine.

    I've done the adaptation, and I can't feel much difference. Gearchanges are perfectly smooth up or down, automatic or manual, and there are no fault codes, so the box may be functioning as MB intended; it shifts automatically down to fourth from 3000 rpm in fifth with kickdown, but just won't go down to third unless changed manually. That seems odd to me.

    Does anybody think there might be a software update available that would make a significant difference? If not, looks like I'll have to live with it...
     
  14. OP
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    E55BOF

    E55BOF MB Club Veteran

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    SORTED!! I contacted the last owner but one (old invoices are very useful sometimes) to see if he could tell me when he last changed the engine oil, and he mentioned in his reply that the car seemed to have got slower during his three-year ownership. Thinking that over, I had a Road to Damascus moment. And the problem was? Throttle cable!

    The throttle was only about two-thirds open at full bore. With the cable adjustment correct, the missing performance is restored; it now goes (much better) as it should, and could probably pull at least a medium-thickness skin off a rice pudding. It still wouldn't frighten an AMG, though (but an AMG Line it might...)

    WOO HOO! :banana::banana::banana:

    P.S I'd mark the thread as 'Solved', but I don't seem to be able to do it through my User CP. Is there a way, does anyone know?
     

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