722.6 Gearbox Change Points

Discussion in 'General Discussion' started by E55BOF, Jun 12, 2019 at 3:33 PM.

  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?
     
  2. Greenmanslk

    Greenmanslk Hardcore MB Enthusiast

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    E55BOF likes this.
  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
    OP
    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
    OP
    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
    OP
    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
    OP
    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...).
     

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