Viewing 9 posts - 41 through 49 (of 49 total)
  • Double declutching and other things your dad taught you to do…
  • thisisnotaspoon
    Free Member

    What coffee king said.

    Normal driving in a normal modern car:

    1)clutch in, engine disengaged from gearbox input

    2)shift to neutral, there are now 3 parts to the system moving independantly, the engine and flywheel, the clutch plate and gearbox input shaft, the output shaft of the gearbox.

    Depending on design theres alos various dog gears, lay shafts etc, but we’ll ignore those and just assume its a 2speed+reverse in a nice simple box.

    The output shaft spins at the road speed.
    The engine spins at whtever you let it.
    The input shaft stops (not entirely, but ‘box oil is pretty thick so its slowed enough compared to the 6000rpm+ it was doing a split second ago and thr 4000rpm you want it to do after the upshift)

    3)Shift into the next gear and the two gears (output and input shafts) are at different speeds, to you have 2 brass ‘cones’ between them, as you push them together the input shaft speeds up, the further you get towards the gear the faster it spins untill they match just as the gears are about to engage.

    4)Hopefully the engine revs now match your road speed (you’ve been off the throttle a split second) so when you relsease the clutch the input shaft is moving the same speed as the engine an everything is nice and smooth.

    double clutch method

    As above, but,

    After (2), release the clutch quickly and press it again, this conects the input shaft to the engine again and gets it spinning, as the pedal comes up push it into the new gear, as both are spinning the syncro cones do no work, and everything meshes smoothely.

    Basicly the clutch slips rather than the cones, and if you’ve ever tried clutch plates are easier to change than a gearbox rebuild.

    TBH, I’ve never bothered, even in the midget, full throttle, clutch down about 3/4 of the way (to the bite point so the input shaft never stops spinning), next gear, revs have rissen as the load came off the engine so the flywheel gives the whole car a kick up the arse as you let the clutch out.

    Edukator
    Free Member

    If your Midget has either the A-series or Triumph engine then you’ll be changing up at between 5800 and 6100. Now if the revs rise from there it is not a good thing. On full throttle I can’t see you changing quickly enough to keep the thing below 6500 which is abouh the point valve bounce will start, a very bad thing.

    thisisnotaspoon
    Free Member

    I run out of nerve/mechanical sympathy kicks in arround 5 (that and a nasty missfire from a cheep condenser starts arround 5k) 🙁 Not somethign I do very often, just when, I fancy a bit of stupidity, normaly I’m a pootler getting silly mpg out of it on a sunny afternoon with the roof down 🙂

    Let the throttle off, but not enough to let the engine speed drop might have been a better description than full throttle.

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    Olly
    Free Member

    so in thicko summary.

    syncro and gearbox layout is as i understood it

    the syncro COULD be thought of as a “kind of” clutch between the actuall clutch, and the road wheels

    double de clutch, re engages the input briefly to maintain the spin of input, to REDUCE wear on the syncro (mini internal clutch, and transfer it to the ACTUAL clutch (by doubling clutch use per change)

    ?????
    assuming i’ve got it right (or near enough) its one of those things that, while it helps the car last longer, it doesnt help the driver at all? (where as blipping, and heel and toe, keeps the car/drivechain from jolting and pushing the car around)

    Tempted to try clutchless shifting in my car, as i can chuck gears in bob on (most of the time :$ but I cant get over the fear or making mechanically sinful noises, so have never tried, and that is probably just as well.

    molgrips
    Free Member

    It doesn’t really help at all unless a) you are a racing driver b) your car is really really old and has no synchromesh or c) your car is a bit knackered.

    On the above mentioned old fiesta 3rd to 2nd would give a little crunch now and then. Double de-clutch made it smooth as.

    For clutchless shifting, just make sure you’re really light with the lever. If the speed’s not right it just won’t go in, there’ll be no crunch unless you continue to try and ram it home.

    The other alternative is to slam it into gear as hard as you can but that’s not recomended 🙂

    Edukator
    Free Member

    Try it Molgrips (it’s not my gearbox 😉 ). You’ll find the decisive movement is better than being light. It doesn’t require much force on a dog box but on a standard synchromesh box you have to use enough force to get past recalcitrant cones that are trying to do their job. That’s a firm shove.

    The only change I could make every time (and it has to be every time because if you fail the loss of drive is going to be hard to manage), was fourth to third. The bend tightens more than anticipated so you left foot brake to kill the understeer (still on the gas). The nose tucks, if it tightens more you brake more to get suitably sideways (still on the gas). The revs are now dropping (along with the power) and a lower gear needed to maintain the poise. No lift of the throttle, just change with a fast, firm, single movement. You instantly have more power. I can’t think of any other time you’d want to clutchless change. (edit this only applies to FWD cars with enough rear brake balance)

    coffeeking
    Free Member

    assuming i’ve got it right (or near enough) its one of those things that, while it helps the car last longer, it doesnt help the driver at all? (where as blipping, and heel and toe, keeps the car/drivechain from jolting and pushing the car around)

    Not quite. Your “blipping” is covered by the ddc method as you need to blip to get the input shaft up to speed, so it’s “blipping” with extra mechanical sympathy and helps speed up your shift a smidge (if you’re good, otherwise it takes longer to do the two clutch movements, you cock up the shift and ram it into gear without a clutch and all goes downhill).

    Generally I don’t but it’s handy on downshifts with my 20 year old box where there’s a slight notch. Even on the box new there always was a slight notch, it just depends whether the driver notices it I guess. My other half never notices and never does it. I replaced the box which required a full engine out job, so I’m very sympathetic to that gearbox now!

    iDave
    Free Member

    going back to what my dad taught me, many gems could fill a book – the most valuable thing was that “your boss will always be an idiot so it may as well be you”

    prettygreenparrot
    Full Member

    Clutch? After driving all sorts of cars & trucks I really can’t be bothered with this clutch/gearstick lark. Let machines work and people think. Automatics for me. Well, except when it comes to bikes. But then that’s a whole other discussion I guess.

Viewing 9 posts - 41 through 49 (of 49 total)

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