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Author Topic: Double de-clutch downshift...  (Read 6640 times)

andrewR

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Double de-clutch downshift...
« Reply #15 on: June 02, 2020, 12:57:04 PM »

Changing gear without the clutch is no bad thing to practice.

Also lost my clutch once and managed to drive right the way across London East-West on the "North Circular" and out the other side to the M4. Again, this was in the early 90's with the same S2 vehicle I still have. A lot of stop-starting, every traffic light needing to start in 1st on the starter motor and then wedge it up by feel. Don't really want to repeat that. Stopping unexpectedly is actually worse because you don't have time to zero the torque on the box and have to yank it out or just stall the engine on the brake if you're not quick enough.

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Andrew

canadianeh

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Double de-clutch downshift...
« Reply #16 on: June 02, 2020, 01:57:00 PM »

Lots of good info here! Thank you.

It's the blip I'm not really getting I guess. My downshift from 3 to 2 is not a happy movement yet.

Not really understanding the tap third before second tip from a start?

Anyways, this is all really helpful and interesting stuff. I continue to learn!
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Mowersman

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Double de-clutch downshift...
« Reply #17 on: June 02, 2020, 02:07:15 PM »

Lots of good info here! Thank you.

It's the blip I'm not really getting I guess. My downshift from 3 to 2 is not a happy movement yet.
It takes a fair bit of practice, though not as much as 2nd to 1st! With 1st, you are actually meshing gear teeth, at least on 2nd you are just engaging a dog clutch.

Not really understanding the tap third before second tip from a start?
It basically uses the syncro on 3rd as a brake, otherwise it takes several seconds for the internals of the box to slow down, which can cause crunching when engaging from a standstill.
Andrew
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Wittsend

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Double de-clutch downshift...
« Reply #18 on: June 02, 2020, 02:12:07 PM »

.... all of which is character building  :first
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andrewR

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Double de-clutch downshift...
« Reply #19 on: June 02, 2020, 02:46:38 PM »

It's the blip I'm not really getting I guess. My downshift from 3 to 2 is not a happy movement yet.

Okay if you are mechanically minded, this is what you need to visualise.
Inside the gearbox, when you're moving down into 2nd, you need the engine-side of the gearbox to be going at about the same speed as it will need to be going once you've dropped into 2nd, BEFORE you stick it in 2nd.

So, your target when you double-declutch into neutral and then "blip" the throttle is you put the engine revs at just over the engine speed you think you'll end up at, before you put the clutch back down again and ease the stick into 2nd.

I say "just over" because in the small time between the throttle "blip" and getting into 2nd, the front half of the gearbox starts slowing down with the oil viscosity, so you ideally account for that.

In time, you'll also find yourself compensating for
- How hot the gearbox is (how long/fast you've been driving). When cold, it slows down a lot faster, so you might need a bit more "blip" or to be quicker. When hot, you need less "blip" or you need to wait longer after the "blip" if you overdo it.
- How much the vehicle slowed down while you made the shift. Depends on gradient etc.

If you can imagine those engine-side cogs spinning, and how they ideally need to be ending up at the same speed as the "output" cogs before engaging, it all makes sense.

Also think about the noise a big old lorry makes, or used to make when you were younger, when downshifting at speed to take a hill. It sounds like it's all for show, but it's all based on a practical necessity.
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canadianeh

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Double de-clutch downshift...
« Reply #20 on: June 02, 2020, 03:35:54 PM »

Thank you,.

I will try and practice this movement at relatively slow speeds and hope for not too much crunching...

If I attempt to move from third to second with the blip and hear the crunch, what's the recovery move? Back to third? If that makes sense.
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andrewR

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Double de-clutch downshift...
« Reply #21 on: June 02, 2020, 04:53:54 PM »

If you only just touched the gears, you might be able to back off. But most likely, by the time your getting the crunch, you're half-way anyway, committed, and might as well press through as the gears will have already come closer to engaging with the initial touch. Only if you don't have the clutch down enough while you engage will you produce a long-lasting grind, and that shouldn't be happening even if you judge the "blip" wrong.
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Forest2a

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Double de-clutch downshift...
« Reply #22 on: June 02, 2020, 06:04:34 PM »

Something of an aside but often the early (as in pre-war, some even pre-WW1!) driving 'manuals' go into great detail about double-declutching.  Indeed, much else besides.  Sadly, I can't lay my hands  on the one I have about somewhere.  I believe it was from the 1920's and published by 'Motor'.  I think it is the same as this one I found listed on Amazon currently.

https://www.amazon.co.uk/How-Drive-Car-Niceties-Control/dp/B01CIG5VHU/ref=sr_1_13?dchild=1&qid=1591116075&refinements=p_27%3AThe+Editor+of+%27The+Motor%27&s=books&sr=1-13&text=The+Editor+of+%27The+Motor%27

There's also a listing for something similar but even earlier, 1 Jan 1900!

https://www.amazon.co.uk/How-Drive-Car-Editor-Motor/dp/B0011BAJ7Q

Can't guarantee they will provide a short-cut to noisless gearchanges but if my (lost!) book is anything to go by they will be a fascinating read.

Neil

(BTW - I've no connection with Amazon or either of the sellers I've linked to!)

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Clifford Pope

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Double de-clutch downshift...
« Reply #23 on: June 02, 2020, 06:10:49 PM »



So, your target when you double-declutch into neutral and then "blip" the throttle is you put the engine revs at just over the engine speed you think you'll end up at, before you put the clutch back down again and ease the stick into 2nd.



Good explanation. That explains why the extent of the blip depends on your speed - if only just rolling along you hardly need anything - the engine will only be going at just over idling speed, so you need the barest hint of a blip.

But on the other hand if you are storming a hill with a full load as fast as you can in 3rd, but you can see the hill gets steeper, you want to get down into 2nd in good time and not lose too much speed. So you need a good throaty blip, because in 2nd the engine will then be going fast.

If you had a rev counter you could actually quantify this, but instint, practice and confidence are better and stand you in good stead.

For real experts, change down into 2nd going downhill with your foot on the brake, turning your heel outwards to blip the throttle while still braking.  :)
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Dentman

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Re: Double de-clutch downshift...
« Reply #24 on: June 02, 2020, 07:30:01 PM »

 :-\
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bill2a

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Re: Double de-clutch downshift...
« Reply #25 on: June 02, 2020, 07:56:21 PM »

All this is true, but you will have more success if you remember to change gear with soft hands, just feel your way into the gears, don’t rush the change.
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Bill

canadianeh

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Re: Double de-clutch downshift...
« Reply #26 on: June 02, 2020, 08:26:23 PM »

Thanks, Bill!

I need someone to do a video of the blip. But I will go to practice today.
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Wittsend

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Re: Double de-clutch downshift...
« Reply #27 on: June 02, 2020, 08:29:29 PM »

I bet there's one on YouTube (somewhere) ???
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Dentman

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Re: Double de-clutch downshift...
« Reply #28 on: June 02, 2020, 11:11:52 PM »

There generally is,  ???
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w3526602

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Re: Double de-clutch downshift...
« Reply #29 on: June 03, 2020, 08:53:52 AM »

I very rarely start in 1st from a standstill. I use 2nd to start off, only using 1st if on a steepish hill or towing.

Hi Alan,

I regret not being able to say I do the same.

For those who know Milton Keynes ... when I take my daughter home, I exit Kinross Drive, from stationary, in first gear ... and am usually in second gear, braking hard from 60mph, on Standing Way, as I approach the roundabout. Don't tell Barbara, it's HER car (Hyundai iX20)

When I left the RAF, I spend a year "mini-cabbing" in South London (50,000miles in my own car). Get to the front of the queue ... and stay there! It saves all that" fuffing" around.  No shunts, but broke two rear springs.

602

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