Manual vs automatic

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  • EssexExile
    EssexExile Posts: 6,110
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    JP08 wrote: »
    Even a 1990s Mitsubishi autobox had the sense to change down on a hill descent ...
    That was the best auto I've ever had.
    Tall, dark & handsome. Well two out of three ain't bad.
  • Richard53
    Richard53 Posts: 3,173
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    Smug b*st*rd here has the best of all worlds. The MX-5 is a manual (how could it be anything else?), the Merc has a lovely lazy slushbox, and the wife's Skoda has a DSG auto. I like them all. I actually enjoy the physical act of driving, so I never mind changing gear, even in heavy traffic. But an nice auto is a pleasure in itself.


    The Skoda DSG is fearsomely good. It anticipates very well, has different modes for the mood you're in, and is as smooth as you like. Economy seems good so far.
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  • Gloomendoom
    Gloomendoom Posts: 16,550
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    Richard53 wrote: »
    The Skoda DSG is fearsomely good. It anticipates very well, has different modes for the mood you're in, and is as smooth as you like. Economy seems good so far.

    The Skoda DSG I have experience of (Yeti) was dreadful at low speeds. It certainly couldn't be described as smooth, quite the opposite. OK most of the time though.

    I drive a car with a big engine and a conventional auto. I also have a manual that requires double declutching to change gears without horrible noises. I like driving both, the latter is particularly satisfying to drive smoothly.
  • knightstyle
    knightstyle Posts: 6,985
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    Anyone thinking they would only go for a torque converter auto should drive a couple of the latest auto cars.
    Our 2.0 diesel Cmax is smoother and much better mpg than our slush box 1.6 perol Juke.
  • Iceweasel
    Iceweasel Posts: 4,684
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    Iwish I understood what a slush-box is. ;)
  • iolanthe07
    iolanthe07 Posts: 5,493 Forumite
    The MX-5 is a manual (how could it be anything else?),

    There are some imported MX-5's around with auto boxes. They come up for sale occasionally.

    Iwish I understood what a slush-box is

    A traditional torque converter autobox. They've been around for decades, are smooth and reliable and easy to maintain. The downside is that they increase fuel consumption, especially when matched with a small engine.
    I used to think that good grammar is important, but now I know that good wine is importanter.
  • Anyone thinking they would only go for a torque converter auto should drive a couple of the latest auto cars.
    Our 2.0 diesel Cmax is smoother and much better mpg than our slush box 1.6 perol Juke.

    Whatever you'll save on fuel you'll spend on maintaining that powershift gearbox, though. I read the wrong service schedule for our car (uses the dry clutch arrangement) and booked it in for the ATF change the wet clutch arrangement needs every three years (or x miles) - £300!!!
  • Joe_Horner
    Joe_Horner Posts: 4,895
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    reeac wrote: »
    The gear ratios were determined by inlet manifold vacuum and engine speed. Both of these applied equally to the two belt/pulley systems. The only way that these systems would know that you were cornering would be that instead of the top belt run being at a greater tension than the bottom run the reverse would be the case. I can't see how this difference between the two sides would cause the front pulleys to change their separations.

    Not quite.

    The front pulley halves (sheaves) are pressed together by springs - so always trying to push the belt to the highest ratio. That's counteracted by springs in the rear pulleys, which are also trying to press the rear sheaves together and move the belt to the lowest ratio. Because the rear springs are (much) stronger, at rest the tension in the top belt run pulls it to low ratio.

    Ignoring the vacuum system for a minute (the transmission works fine without it but isn't quite so responsive and you have potential problems after a quick stop):

    As the car (not the engine) speeds up, centrifugal weights in the front pulleys add to the force of the springs and push the front sheaves together harder. At around 10mph road speed the extra force is enough to start overcoming the rear pulley springs and the belt is pushed towards the outside of the front pulleys & pulled towards the inside of the rear - the ratio increases.

    But, if one wheel encounters extra resistance (as the inner wheel on a turn does with fixed drive) then tension increases in the belt, which effectively "assists" the rear pulley on that side and pulls thr ratio lower.

    The vacuum system is just a refinement and will either assist change up - at low throttle openings - or assist change down - at high throttle or when braking - depending on the position of a distribution valve attached to the carb (on models 30 - 46) or electrically operated by a microswitch on the throttle linkage on the 55 / 66.

    It's ot as complicated as it sounds, and ridiculously easy to work on once you've found your way round it!

    The main reason for adding a traditional diff on the 66 was that they also used the same transmission, but with a single belt, on the 46. Because it was single belt there was no diff effect so one had to be added.
  • Richard53
    Richard53 Posts: 3,173
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    iolanthe07 wrote: »
    The MX-5 is a manual (how could it be anything else?),

    There are some imported MX-5's around with auto boxes. They come up for sale occasionally.


    I know that. What I don't understand is why anyone buys one. It's a bit like putting a towbar on a Caterham.

    iolanthe07 wrote: »
    Iwish I understood what a slush-box is

    A traditional torque converter autobox.
    I think you may have missed a hint of irony here :)
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  • reeac
    reeac Posts: 1,430
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    Joe_Horner wrote: »
    Not quite.

    The front pulley halves (sheaves) are pressed together by springs - so always trying to push the belt to the highest ratio. That's counteracted by springs in the rear pulleys, which are also trying to press the rear sheaves together and move the belt to the lowest ratio. Because the rear springs are (much) stronger, at rest the tension in the top belt run pulls it to low ratio.

    Ignoring the vacuum system for a minute (the transmission works fine without it but isn't quite so responsive and you have potential problems after a quick stop):

    As the car (not the engine) speeds up, centrifugal weights in the front pulleys add to the force of the springs and push the front sheaves together harder. At around 10mph road speed the extra force is enough to start overcoming the rear pulley springs and the belt is pushed towards the outside of the front pulleys & pulled towards the inside of the rear - the ratio increases.

    But, if one wheel encounters extra resistance (as the inner wheel on a turn does with fixed drive) then tension increases in the belt, which effectively "assists" the rear pulley on that side and pulls thr ratio lower.

    The vacuum system is just a refinement and will either assist change up - at low throttle openings - or assist change down - at high throttle or when braking - depending on the position of a distribution valve attached to the carb (on models 30 - 46) or electrically operated by a microswitch on the throttle linkage on the 55 / 66.

    It's ot as complicated as it sounds, and ridiculously easy to work on once you've found your way round it!

    The main reason for adding a traditional diff on the 66 was that they also used the same transmission, but with a single belt, on the 46. Because it was single belt there was no diff effect so one had to be added.
    My recollections must come from the Owners Manual and we owned the car in around the early 1980s so I might be rusty but Wiki agrees with me that it was engine speed, not road speed that counted and clearly the front pulleys were connected to the engine rather than the rear wheels. Wiki also mentions the stresses and breakages caused by the lack of a true differential and, as I said earlier, we had two broken drive belts .... both times after turning a sharp corner. Interestingly, the car drove very smoothly with just one drive belt. As a plus point, I did once climb up a very icey driveway thanks to the limited slip effect.
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