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Naive Auto question ?

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  • Naive Auto question ?

    Hi,
    I've had my diesel NS Pajero SWB for nearly a week now and as this is the first car with an automatic transmission that I've owned, I have what is probably a very silly question. Does the Pajero have a mid gear in between 4th and 5 th ?
    The reason I ask is when traveling on the highway at roughly 100 km/h (generally set with cruise control) the tacho shows about 2000 rpm, when a largish hill comes along the transmission feels like it changes down a gear and the tacho shows 2250. If I use the triptronic bit of the Auto, it shows I'm still in 5th gear and if I manually change down to 4th gear at 100 km/h the tacho shows roughly 2700 rpm.
    I've had a quick look in the manual and can't find any info, so I'm hoping someone can enlighten me as to what is happening.

    Thanks Jeff.
    NS Pajero SWB R, Diesel, Automatic, BFG AT/KO's, AirTech Snorkel, LRA Auxillary Tank, Dual Batteries, Thule Aerobars & Roof Box.

  • #2
    Jeff you'll find this is the gearbox torque converter unlocking. For more info check out http://auto.howstuffworks.com/torque-converter.htm

    You'll probably find something on this forum as to its function as well if you dig around.

    Mike

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    • #3
      Originally posted by Endorphin View Post
      Jeff you'll find this is the gearbox torque converter unlocking. For more info check out http://auto.howstuffworks.com/torque-converter.htm

      You'll probably find something on this forum as to its function as well if you dig around.

      Mike
      Thanks. Now I know what it is called I'll check around for more info.

      Bye Jeff.
      NS Pajero SWB R, Diesel, Automatic, BFG AT/KO's, AirTech Snorkel, LRA Auxillary Tank, Dual Batteries, Thule Aerobars & Roof Box.

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      • #4
        Torque converter lockup is all about efficiency. Ie a torque converter is a fluid coupling and has a loss associated wtih it due to slip in the coupling. TO maximise efficiency, modern torque converters physically lock to ensure zero slip and therefor maximum efficiency of power transmission from the engine to the wheels.

        As you go up a hill the load is directly transmitted to the engine and as the engine loads at some point to reduce the burden and allow the engine to work in a better point of the power torque curve the coupler is unlocked, some slip is introduced but the higher torque times efficiency leads to a level of torque transmission to the wheels which may cope with the load of the hill, if not the gear box may then respond by dropping a gear.

        I think that the article lines up with this.
        Dan C; Stock NS Exceed DID Auto w T'bar, Magellan Explorist XL w DAST topo, Tom Tom One

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