The bizarre John Lyon quiz linked to in another thread today made me wonder. I've read about DD, as we shall call it here. I even found some discussion of it among some self-professed advanced drivers on another forum, which at least explained the principle of matching input and output speeds before re-engaging.
So, out of curiosity, I tried it out, on a familiar bit of road and in light traffic so all the left-foot faffing wouldn't get in anyone's way. And do you know what? I could find no discernible difference in the quality or smoothness of the gearchanges; they just took four times as long.
Now, I presume our own Mr Pillar has a use for this, but does anyone here ever do it with more recent machinery? Or is my instinct, that a certain type of pipe-smoking AD still does it because he can although there's no earthly use for it, closer to the mark?
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The only time I have ever double declutched was to persuade my old Focus into reverse on a cold morning. Never needed to at any other time - thats what synchromesh is for.
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Never bother with it either. I have never noticed a difference in smoothness in any car I've driven.
Heel and toeing is worth doing though. Coming down through the box is so much smoother. One of my school mate's dads was so good at it, he could change down through the box without using the clutch. Apart from the engine noise, you couldn't tell he'd changed gear, it was that smooth.
I'm nowhere near that good at it, but it still makes a difference done half decently :-)
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I occasionally double declutched on agricultural tractors when the going got very sticky and it was important to change down and maintain forward momentum at the same time.
Double declutching is harder with a hand throttle and 10 inches of clutch travel, but in a field there's no need to worry too much about steering or other vehicles.
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I used to regularly change down in my BMW without using the gears at all - just matching the engine speed correctly.
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>>I used to regularly change down without using the gears at all
Wow! thats good! ;-)
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>> >>I used to regularly change down without using the gears at all
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>> Wow! thats good! ;-)
>>
Oops - that would be clutch of course!!!!
Watta mistaka to maaka!
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Only times I've done it is with awkward reverse gears or an old cinquecento that would scrunch 3rd gear if you didn't. Otherwise a careful gear change is just as smooth
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I learned to double-declutch in the 1960s largely because Sir Alec Issigonis didn't believe in syncromesh on first gear. I don't see the need to do it now, but I do still think that revving a little before changing down when going uphill is kinder to the engine and helps with a smooother gearchange.
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As above, used to do it to change down into 1st from 2nd in my old Triumph Herald, although that was not necessary very often.
Haven't done it for years now.
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Double-declutching is still useful on a cold 7.5t lorry for the first half-dozen gearchanges away from the yard - the gearbox oil gets a bit treacly with the miles.
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I learned to double declutch whilst learning to drive in my Dad's Maxi 1750HL. At a year old, the synchromesh on several forward gears had worn out (they all do that sir, said the dealer), so it was pretty much the only way to change down through the gearbox. I remember my driving instructor being astonished when I double declutched my round the gearbox in the driving school Fiesta.
I've kept it up through force of habit and having owned several cars which had no synchromesh even when they were new. I still do it if driving a car with manual gearbox.
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I don't see the point or any advantage of doing so with synchromesh.
Crash box trucks it sort of helped, but in practice you learned to match speeds so developed the technique (advised for Fuller boxes if my memory serves).
That was to depress clutch half way as you slip out of one gear, then fully just before selecting the next.
In practice you didn't need half that faff if you meshed speeds properly, some boxes needed fast no nonsense shifts (ancient Fodens with own box) if you didn't want a dislocated wrist, and some needed slower just feed it gently until it slips in, David Browns.
I can't change gear clutchless very well at all with synchro boxes but constant mesh crash boxes no problem, in my humble synchro boxes should not be in trucks anyway, too slow and imprecise.
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I had a 1929 Riley 9. I HAD to double declutch.
Learned to change gear with no clutch..
Thing of the past.. (did it on tractors as well).
Historical curiosity...
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When I first drove my friend's LWB diesel Defender a few years ago I found, to my surprise, that I began to DD as if I had never stopped. And I've been driving automatics for 30 years. Certainly seemed to smooth out the Defender.
Incidentally, I had a couple of Hillman Imps decades ago and the only time you needed the clutch was to move off, they were that good.
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The orginial VW Beetle after moving off I could change gear without using the clutch.
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Some random memories about DD and clutchless changes.
Dad had the village garage when I was a nipper and was used to a variety of cars with knackered clutches and gearboxes. He claimed to be able to do clutchless changes but wouldn't on the Mk1 or Mk2 Zephyr dropheads we had, owing to the slack in the column shift. He made a face at me through his beard and said, "I'm no fisherman" to back that up. Later he took me to from Harrogate to Grantham in our Mk2 Jag and only used the clutch a couple of times to set off and in traffic.
My first car was a 1961 VW Beetle and I could change gear in that without the clutch. I may have mentioned this during my time at Olivetti and was challenged to do a journey in a works Mk1 Escort van, having flatly refused to use my own car, a Fiat 1500 with column shift. I managed to travel from Leeds to Doncaster without using the clutch at all, starting the van in 2nd gear and turning the key off at lights. What a sweet change the Escort had! My "observer" stuck a post-it note on the clutch pedal and produced it as evidence that I completed the challenge. I won a great deal of beer for that and the Escort van appeared no worse for its ordeal.
The most critical DD change was 2nd to 1st towing the caravan up Holme Moss with an asthmatic Citroen D Special. I shouldn't have been on that road but that's another story. Column change again and no synchro on 1st; made me sweat for a couple of seconds but ended up OK. If I'd had to stop I was certain that I wouldn't have been able to restart.
When I was learning how to ride a motorcycle 10 years ago I found the clutch action stiff for a lifetime desk pilot as I was then, and I learned how to do clutchless changes. The first time I did it the instructor bawled me out, so I developed a hand action to mimic pulling in the clutch so she could find something else to shout at me for.
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I used to change up without the clutch on the Norton of '66 vintage. As has been said, bikes have constant mesh boxes, so no big deal in avoiding the clutch once moving. But I find it difficult to see how a driver could match revs whilst changing gear on a syncromesh box. Double-declutch is OK, there is opportunity to blip/decay engine revs. How is it done, by the cognoscenti?
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The lancer gearbox is a little obstructive. Out of first is slow, so needs a blip you press the clutch, and third down to second needs heel and toe. Fortunately the brake/throttle is perfectly placed to make this an action of second nature.
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>> The lancer gearbox is a little obstructive. Out of first is slow, so needs a
>> blip you press the clutch, and third down to second needs heel and toe. Fortunately
>> the brake/throttle is perfectly placed to make this an action of second nature.
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Sounds like a crap car......or driver. :-)
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>> The lancer gearbox is a little obstructive. Out of first is slow, so needs a
>> blip you press the clutch,
ISTR you're looking to change the gearbox oil Z, maybe that will help.
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>> I don't see the point or any advantage of doing so with synchromesh.
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>> Crash box trucks it sort of helped, but in practice you learned to match speeds
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>> I can't change gear clutchless very well at all with synchro boxes but constant mesh
>> crash boxes no problem, in my humble synchro boxes should not be in trucks anyway,
>> too slow and imprecise.
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I'm inclined to agree with you GB; as you well know Volvo FM boxes are virtually impossible to use sans clutch, and not brilliant with it. ISTR you like me are a fan of the Eaton Twin-split, lovely box to use.
The old Fuller boxes were a joy to use, provided you reminded yourself which lorry you were in, ERF and Seddon-Atkinson gates being mirror images.
I do have to double declutch downwards with my old pick-up as there's no synchro in first, ditto when I had old Land-Rovers; mind you I was first introduced to the art on bull-nosed Commers in the army and there's no doubt that, like a lot of the old lorry-driving skills, it's a useful one to have.
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I have to say I'm aware of DD but I've never been taught it and never tried it. It seems to be an age thing, but of an odd one out here, I take it was quite common to be taught such things years ago?
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>> I have to say I'm aware of DD but I've never been taught it and
>> never tried it. It seems to be an age thing, but of an odd one
>> out here, I take it was quite common to be taught such things years ago?
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Was not taught when I learned to drive: nearly half a century ago .. eek!
Had to learn it myself.
By then ALL modern cars had syncro 1,2,3,4.
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>> I'm inclined to agree with you GB; as you well know Volvo FM boxes are
>> virtually impossible to use sans clutch, and not brilliant with it. ISTR you like me
>> are a fan of the Eaton Twin-split, lovely box to use.
Agreed, Eaton twin Split in my humble was the best gearbox ever fitted to a truck, took a little and sometimes a lot of getting used to but once mastered had no equal in speed of change and therefore total vehicle control, kept idiots out of the driving seat too.
Apart from Scanias early splitters as fitted to 111 and Volvo's 86 and 88 range changes i've never found a later Swedish manual box to be any use at all....mind you Volvo's auto manual stand apart from all other automated manuals, it is truly excellent....but then the competition is so dire without a glimmer of competence it couldn't help but look brilliant.
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I suppose I've always done it on the downshift in manuals when, er, um, pressing on...
Almost certainly not necessary and quite possibly not even slightly useful on modern kit but I've always felt, especially if conditions are slippery, that it significantly reduces any chance of engine grab and dreaded understeer.
Anyway, on anything with a decent engine it makes a nice noise so there...
:-)
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There's a really good technical reason to keep synchro away from truck gearboxes.
With a crash gearbox it's very difficult to select a gear which will overspeed the engine when the clutch is brought up. While a synchro gearbox will take a while to synchronise a gear which is too low, a persistent dullard can easily wreck an engine this way.
Mercedes trucks used to have a speed sensor on the gearbox input shaft connected to the buzzer to warn of a potential engine overspeed, and hopefully prevent the gear being selected and/or the clutch being raised.
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We used to have a rachet system on the tugs.You could not go from full ahead to full astern.Not healthy for the engine.
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.Not healthy for the engine.
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Or, I suspect, for anyone standing at the bow!
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Do it all the time and I'm young. So, those of you that don't do it, would you be kind enough to answer the following and help me understand please: You're on a B road, long straight, 60 mph in, say, 5th. Bend approaching. (well, strictly speaking, you approaching the bend but you understand I'm sure...) Having assessed the bend and lost a little speed, it looks good for taking at about 50. No braking needed but you want a lower gear for better car control. How do you take that lower gear smoothly without DD? I can only guess that you're going to dip the clutch, take the new gear, and raise the clutch. If you don't do something to match engine revs to new gear you'll not have a dead smooth change. Yes, you can increase revs as you raise the clutch, but it's half a job and ham fisted.
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>> You're on a B road, long straight, 60 mph in, say, 5th. Bend approaching........
No braking needed but you want a lower gear for better car control. How do you take that lower gear smoothly without DD? I can only guess that you're going to dip the clutch, take the new gear, and raise the clutch. If you don't do something to match engine revs to new gear you'll not have a dead smooth change. Yes, you can increase revs as you raise the clutch, but it's half a job and ham fisted.
One reason some RWD cars end up in the ditch backwards......
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>> Yes, you can increase revs as you raise the clutch, but it's half a job and ham fisted.
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I am sure that is what 90% of drivers do automatically and smoothly. As you are a youngster it will come with experience.
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Thanks ON, I was being tongue-in-cheek. I'm 47. I probbly do lack driving eperience though and we can all improve. Assuming we don't all think we're brilliant already...
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I'd brake the 10 mph needed to take the corner, change gear, then steer around the corner.
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All my instructors on Police driving courses insisted we double declutch. This would be arounf 1967 to 1974 and all the cars were modern with synchro boxes...Hunters, Cortinas, Jags,,etc.
I rather think the reason was to do with not braking when changing gear...up or down. I did it as a matter of course for years afterwards in my private motoring and still do in the Jowett sometimes..
Everyday cars have consigned the pedal and knob to the bin of time and will do so as long as slushboxes are still available !
We were also taught never to use the gears to slow down, the brakes were for that.
Double declutching from 4th to 3rd, say, was purely to get a wriggle on if you needed rapid acceleration.
Ted
Last edited by: Ted on Wed 18 Apr 12 at 22:15
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Double-declutching is used to synchronize the crankshaft speed with the gearbox input shaft speed. Some time in the 1930s synchromesh was invented, 'a device' as my Bentley's handbook called it, to perform this task automatically. Like my Bentley, most cars until the 1970s had synchromesh only on the higher ratios. First and reverse didn't have it, so if you had to change into first gear on the move, a rare event for a good driver, then you had to double declutch if you didn't want to risk an audible crunch.
The three-speed gearbox of my first car, a Citroen Light 15, had knackered synchro (it wore out you see like everything else) so needed double-declutching on all gearchanges given the wide gaps between ratios. This led to clutch cable problems but never mind that. Probably as a result of clumsy driving by previous owners, I later owned two cars - a Skoda Estelle and an Arna - that had synchromesh damaged on one or more gears. I could drive them all right but not everyone could.
I still DD when changing into first on the move (it does happen sometimes). Can't break the habit. I often wish that like Slidingpillar or a Bugatti owner, I had a car that demanded this seldom-needed but satisfying skill. One doesn't have that many after all.
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I forgot and shouldn't have.
There was another reason truck drivers of old learned to change gear without the clutch, those old clutches didn't have air assistance and required a hell of a shove to press it down every time, and very hard to hold down in traffic, sometimes two feet required and i'm quite serious here.
Heaviest i can recall was Scamell Crusader, but Foden S39 not far off, i spent years in these old battlers and the left knee doesn't forget.
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Interesting debate. My Morgan 3 wheeler only has two gears and on the level, will plod along at about 12mph at tickover in top gear. Upchanges, if you time it right, go in almost like a modern car.
The vintage motorist often hated changing down and clutches were often slipped and ignition much retarded. So double declutching may not have been a universal skill, even when gearboxes said they needed it.
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>> The vintage motorist often hated changing down and clutches were often slipped and ignition much
>> retarded. So double declutching may not have been a universal skill, even when gearboxes said
>> they needed it.
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Could also have something to do with the gear ratios, or more to the point the lack of choice therein. Both my side-valve Harley and the GMC have 3-speed boxes, and there's a sizeable gap between second and top, which necessitates double-declutching or at least a blip of the throttle to reduce the risk of breaking traction, especially on a wet road. Despite Ted's comments above I suspect that many did use the gears to slow down as braking systems back in the day were far less efficient, and being drums were more liable to overheat and fade .
Older engines were more flexible too, and (particularly for sidevalves) since they generally had longer stroke and heavier reciprocating mass than today's buzzboxes the accent was on torque rather than horsepower, hence it was easier to retard the ignition and slog up a hill rather than thrashing it in a lower gear.
Last edited by: Harleyman on Wed 18 Apr 12 at 23:31
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>> hated changing down and clutches were often slipped and ignition much retarded. So double declutching may not have been a universal skill, even when gearboxes said they needed it.
You can say that again. Who knackered the synchro on the old cars one used to drive? I've been driven by many who learned to drive in the crash gearbox days, and crash usually meant crash where they were concerned. The six successive movements of hand and foot, or the seven successive movements of hand and both feet, needed for a double-declutch up or down represented a terrible coordinatory challenge to some old drivers I've been driven by.
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>Heaviest i can recall was Scamell Crusader, but Foden S39 not far off,
Would that be the Foden that my dad called the "40-tonner" that none of the drivers wanted to take out?
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>> Would that be the Foden that my dad called the "40-tonner" that none of the
>> drivers wanted to take out?
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One of these, my first artic tractor as it happens
tinyurl.com/74yvsc7
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Well explained AC.
I have been trying to make clear that DD is to do with synchronising the gearbox speeds, so that you can engage a straight-cut cog that has no synchro-cone.
It has nothing to do with synchronising engine speed to road speed to avoid a jerk that might induce skidding etc. That's just normal good practice, although you do hear people driving in blissful ignorance of the unpleasant jerky power take-up.
DD with a working synchro gear seems to me to be pointless. Let the synchromesh do its job - there's no point in having it and wearing your clutch as well.
In any case, with a synchromesh gear you have no means of knowing whether your DD was correct or not - any mismatch of speeds would be covered up by the synchro action.
I have owned several cars that really did need DD, including my current Series II LandRover, which has crash gears on 1st and 2nd. There is rarely any need to change from 3rd to 2nd at any kind of speed, but on occasions an ability to DD and heel and toe is useful.
Properly done DD takes no longer. You do the extra blip in the middle while moving the lever - it's all part of one steady action.
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I don't do it because (a) it's not necessary with a synchromesh gearbox, (b) it makes gear changes take longer and (c) it puts extra wear on the clutch and the clutch withdrawal mechanism, the accelerator mechanism and possibly also the gearbox.
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I bought a 6 year old Vauxhall Carlton estate for £500 in 1986 when I had to sell my decent car to help fund my 1st house purchase. It had covered about 90,000 miles and had probably suffered some abuse at some point in its life as it had no syncromesh on 4th (top) gear so you had to double de-clutch from 3rd to 4th and at speeds of over 60 mph you had to hold the gearlever in place with your left knee or it would jump out of 4th on the over run.
All it received from me was a 6 monthly oil & filter change & it trundled on for 3 years until I px'd it for a Renault 18 GTX !
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>> until I px'd it for a Renault 18 GTX !
I had a Renault 18 GTX estate and liked it a lot. It was fairly economical, decently brisk, quite refined and very comfortable.
It didn't need double-declutching because it had synchro on all gears I think. If you listened carefully, you could hear the synchro working with a muted zizzz during gearchanges.
Most synchromesh systems can be 'beaten' by drivers making violent snatch gearchanges. If you try hard you can make a crunch changing gear, a crunch that represents damage being done. Eventually the synchro becomes too weak to work properly and the bottom of the gearbox is full of steel filings and shards.
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Double declutching: any takers? - Alastairw
