The Great Double-Declutching Debate (Split from Tips)

I’ve read all the interesting stuff about syncro’s and baulk rings, all correct I might add, then there was the mention of double de-clutching and that got me to thinking how it was back in the days of old(ish.) In 1979, I trained on a Ford “D” series medium range artic with a 4 over 4 syncro range change, no problem there. That configuration is still very familiar today.

I clearly remember asking why we HAD TO double de-clutch every gearchange, and being told that not all wagons had syncro gearboxes. I was told that we had to satisfy the examiner that we could competently drive a non-syncro gearbox safely. (The sort where the instructor said “it’s a gearbox, not a juke box.” Or, “there’s 8 gears in there, can’t you pick one of them?”)

After the compulsory apprenticeship on rigids, I was given an Atkinson (240 Gardner, Oakley’s, Hereford) to run at the then limit of 32 (proper) Tons. Imagine a novice driving that around Stoke-on-Trent (hilly city centre with no by-pass back then.) without the ability of double de-clutching and a quick rev to get the gear? I believe that double de-clutching should be covered in the training in case somebody is given a truck that’s had the kind of abuse that Lucy suggested. How would a newbie drive that then? It’s still all about safety isn’t it?

Diesel Dave:
I believe that double de-clutching should be covered in the training in case somebody is given a truck that’s had the kind of abuse that Lucy suggested. How would a newbie drive that then? It’s still all about safety isn’t it?

Yeah, but given as Rog has already highlighted the amount of difficulty trainees have with learning to use a range change box, don’t you think a detailed explanation of how, why, when and when not to double-declutch is unnecessary information overload?

The basic level LGV Instructor is there simply to get the candidate through the test, not to try and replicate the knowledge gained by experience. Passing the test only “allows the driver to continue to learn unaccompanied”, it doesn’t teach you to drive. That takes time, practice and, yes, I agree, we need more training - but keep stuff like that “post-graduate”.

There are very few constant mesh boxes still out there, and as a consequence fewer and fewer knackered synchro boxes which have been abused. Tell a newbie to double-declutch in a screwed synchro, and you can bet your life they will do it in ALL synchros because they haven’t got the experience to tell whether each one needs it or not…And so the whole cycle will start again.

Double declutching is off the syllabus with good reason. It’s obsolete. So long as our green-as-grass newbie has the good sense to ask for help in the unlikely event they encounter a constant mesh box, they will be absolutely fine. Hell, even synchro manual boxes are increasingly on the way out in favour of AMT, after all - and I have yet to come across a non-specialist trainer who has the faintest clue how to use those boxes at all!!!

Totally agree with lucy on this one (god i hate doing that )

All the trainee needs to worry about is that 1hr of hell “NOT” the lifetime of sheer misery to follow … After all you dont want to spoil the moment we all have when we think “why the [zb] did i decide to do this for a living” )

But then on the other hand if you do info overload your trainee’s ROG then at least you/your company will make more money out of it as it would take that many more lessons to pass your test (you havent started working for clearstone have you ROG??)

Reef:
(you havent started working for clearstone have you ROG??)

Most definitely NOT

I do not introduce anything extra into the basic DSA test training format unless the trainee needs it or would benefit greatly from it.
If a trainee can go from gear 2 to gear 1 without any problems then why confuse them with double-de-cluching or blipping the throttle - it would not make sense

I believe that double de-clutching should be covered in the training in case somebody is given a truck that’s had the kind of abuse that Lucy suggested. How would a newbie drive that then? It’s still all about safety isn’t it?

I usually double de-clutch out of habit and agree that it should be part of the training. I am often asked by new drivers to show them the technique for DDC and always find the time to explain the why and the how and the benifits.
You never know when you will need it - there are still some **** old motors out there.

When I did LGV instruction, I was sometimes asked about DDC as Mothertrucker has also found. I’d explain that it was for non-syncro gearboxes and certain syncro gearboxes that had been abused. Sorry for being old, but it was actually required when I did my HGV1 test in 1979. On my test, the whole of my gearchange exercise had to be completed by the DDC method.

I also agree with Lucy that DDC might be info overload for candidates, but I found that some gearboxes don’t have a syncro on first gear. BTW, that’s also true for some cars. Given that the gearchange exercise is still a current DSA test requirement, I believe that it’s probably beneficial for a candidate to spend a short time to at least be introduced to the technique.

My own view is that it would be info overload for a candidate if I’d gone on about the transmission brake at the bottom of the clutch pedal travel, because that would quickly be identified by an old hand when the newbie jumped in a truck with an Eaton twin-split. The Fuller Roadranger also required a certain technique. As ROG said, “unless the trainee needs it,” or as I suggest, if the truck to be used for the test happens to have a “tired” gearbox… Seems like another collection of good ideas from old hands… with the caveat that there seems to be a time and a place for all our good ideas.

As for constant mesh gearboxes, I agree with MM. Personally, I prefer them to a syncro box all day any day.

DDC was still a requirement when I did my test in 1992. The truck I was trained in did have synchro on all but crawl but of course that gear was required on the gear exercise. Not a problem for me as a regular driver of a Series 2 Land-Rover (no synchro on 1st or 2nd).

Can anyone explain how DDC damages synchromesh? I know what goes on in there and have even been brave enough to overhaul a couple of car boxes. When engaging a gear in a constant mesh box the driver has to match the speed of the input or lay shaft to the gear being selected so that the splines will simply slide over each other and engage smoothly (OK, actually you need a tiny difference to avoid matching them exaclty wrong if you know what I mean!). In the 1920s someone invented synchromesh as an add on. As the gear is selected the hub slides over the cone and if the speed isn’t matched friction will speed up/slow down the shaft to help match the speed. about 30 years later the system was refined further with baulk rings using spring loaded bearings to prevent the gear being engaged until the speeds were close enough (these are the bits that explode all over the garage when you take them apart). This enables gears to be changed without skill but does make the lever heavier as well as the unit more complex and expensive to build.

As has been pointed out if you try to change down to a gear much lower than you should you can actually hear the box whine. If the baulk rings are doing their job is should be impossible to force the splines together with a crunch.

Now, every time you change gear, particularly a down change, the synchro does its job and as it’s using friction it wears out a bit until the day when it can no longer cope. If you try to engage a gear when the speeds are perfectly matched it has nothing to do so no wear occurs. That’s why a synchro box feels much smoother if you DDC. (I don’t - I’ve taught myself not to)

So, how can eliminating friction increase wear?

Can anyone explain how DDC damages synchromesh?

I would like to know the answer to this as well.

Can anyone explain how DDC damages synchromesh?

It doesn’t.

Thanks Zetorpilot

It does. It forces the cones to work harder, which in turn prematurely wears them. De Saint over on the PDA posted a very comprehensive explanation at one point (he’s a wagon mechanic by trade) but I can’t seem to find it at the moment, may have dropped off into their archive. That was the jist though, and is bourne out by experience.

Sorry Zetor, but you are wrong on this one. Will keep searching for better info for you.

I think this discussion might have turned into a “form of words” question.

I don’t believe that the action of DDC in itself damages syncros, but I do believe that syncros would be damaged by having by being forced to cope with the mis-matched speeds of two shafts in the gearbox, whether DDC was used or not. IIRC, it’s the forcing that creates the wear/damage.

I’d still say that, a test candidate would be well advised to learn and master the DDC method, if it’s known in advance that the truck to be used for the driving test has a “tired” gearbox.

So tell me Dave…

…In between the poor sods trying to master the gearchange exercise with a whole extra range that they aren’t familiar with…get used to the size of the vehicle and it’s blindspots…learn a whole new set of road positions and turning circles…suss out the reverse…and iron out all the bad habits they’ve picked up driving a car/rigid/whatever…all in around 5 days, if that, and with the pressure of expense and a test at the end of it…

…where exactly are our beleaguered students supposed to find time and concentration for a lecture on when and when not to DDC…why they shouldn’t do it on a synchro box that’s not knackered…how to tell whether it is knackered or not - bearing mind that newbies often find it harder to engage gears in a box with nothing at all wrong with it, simply because truck boxes are stiffer than car ones - without causing damage in the process…and all the other stuff which has come up in the post above, without causing COMPLETE[/i] overload?
The solution is simple. If a training vehicle has a synchro box which is bad enough to need the throttle blipping and all that jazz, REPLACE IT! IT’S KNACKERED!
This sort of knowledge is the kind gained by experience after acquiring the basics. That’s what the Driver CPC will be for, as well as the ongoing training which will be needed to keep it current, and in the meantime can be taught and learnt on the job by which point it might actually mean something to the driver on the receiving end!!!

There are so many different types of gearboxes on trucks that how could you really train a student to use them all?

Maybe if it comes up in conversation an instructor could explain the principle to a student, but most drivers are more likely to some across the various auto and semi auto boxes in their driving careers than a Twin Splitter or something similar.

Off on a tangent it amazes me that Haulage companies spend thousands on new trucks with the latest gearbox because it will save them money in fuel and maintainence, but fail to bother to teach the driver how to get the best out of it,

and also some drivers who won’t change change their way of driving because that’s the way they always did it and why should they change their driving because of some new fangled technology.
Of course they have no problems using thier mobile phone, DVD player, or sat nav or any other gaget that’s around, but they’re expert drivers so nobody can tell them anything about driving.

All very true Lucy

Having done LGV instruction for several training providers, I’d say that some of them have an attitude leaves a little to be desired. (I’m being very polite to them there.) However, from experience, I’d say that training providers will have a training vehicle repaired promptly if legally required items are defective. IMHO, training providers aren’t that different to the average haulage company when it comes to maintenance/repairs.

How do you think your boss would react if you reported worn syncros on a vehicle that you’d been asked to drive? I’d suggest that we both know that there wouldn’t be a legal reason for a driver refusing to take it out on the road. I’ve tackled training providers on that very point, and had it pointed out to me that, after passing their test, a candidate might well find a “tired” but otherwise perfectly servicable gearbox on a truck at any time.

Since this question relates to LGV training, I have to admit that I don’t have the current DSA guidance to instructors. Mothertrucker or ROG, to name but two, might well have the definitive answer to the question of whether DDC is required. If it is, then our opinions might be irrelevant, because a candidate might then be “failed” for not carrying it out on test. Apart from that, I’d reiterate my last post as to the question of damage.

But Dave, an experienced driver refusing to drive a box with worn synchros is a million miles away from a newbie being taught to pass a test in a vehicle which is defective. If an inexperienced driver encounters such a box, they can always ask someone with more experience how to cope…a newbie needs to be given the correct tools to get throught their test without unnecessary complication, and DDC-ing a knackered box rather than haviing a decent one to learn in is exactly that. Just because hauliers send their experienced drivers out in it doesn’t mean it’s good enough for teaching, the two scenarios simply aren’t comparable.

If you read above, you’ll see that ROG says he does NOT teach DDC unnecessarily -

ROG:
I do not introduce anything extra into the basic DSA test training format unless the trainee needs it or would benefit greatly from it.
If a trainee can go from gear 2 to gear 1 without any problems then why confuse them with double-de-cluching or blipping the throttle - it would not make sense

That would kind of hint that it is NOT in the syllabus - and why should it be? This is 2007, not 1987, and the chances of any driver encountering a constant mesh box under any circumstances (other than as AMT, which is a whole other kettle of fish and also doesn’t need teaching at test) is pretty minute and getting more so by the day. It is perfectly reasonable these days for a driver unfamiliar with such a box to be given a “crash course” (pardon the pun) upon encountering one…there is simply NO need WHATSOEVER to teach it across the board!

As for the nitpicking over whether or not DDC damages synchros, suffice to say that whatever words you dig out in an attempt to ensure that everyone is right, and no matter how you dress it up, DDC a synchro will cause damage, by whatever means you wish to use to describe it.

Lucy:
As for the nitpicking over whether or not DDC damages synchros, suffice to say that whatever words you dig out in an attempt to ensure that everyone is right, and no matter how you dress it up, DDC a synchro will cause damage, by whatever means you wish to use to describe it.

Sorry Lucy, on this one you’re wrong, there’s no factual evidence to back that up, as a fully qualified technician, of too many years to admit , I’ve stripped and repaired all sorts of boxes, when it was more economical to do so, and as was earlier explained a synchro unit is only a form of clutch to aid shaft speed matching, if as the operator you can match those speeds then you, esentially, make the synchro’ redundant, not damage it.

I will agree that trying to teach it inside 5 days on top of everything else is overload IMHO, there’s enough to take in as it is.

I was taught to DDC way back when and still do it, having had a problem with the box on my unit recently [Daf 95 XF] which resulted in a rebuild I was told that the only thing that got it back was that ability to DDC and in their opinion {a truck transmission specialists} if more drivers were capable DDCing there would be less 'boxe for them to rebuild.

Interesting skorpio, thanks for that. Am going to have to get hold of De Saint from the PDA for his explanation again now!

Lucy:
But Dave, an experienced driver refusing to drive a box with worn synchros is a million miles away from a newbie being taught to pass a test in a vehicle which is defective.

Agreed. However, a training school won’t replace a gearbox if the only defect is a syncro. We shouldn’t forget that a large number of gearboxes don’t have a syncro on first gear, and that the gearchange exercise must involve first gear. (DSA requirement.)

Lucy:
If an inexperienced driver encounters such a box, they can always ask someone with more experience how to cope…

Agreed.

Lucy:
a newbie needs to be given the correct tools to get throught their test without unnecessary complication, and DDC-ing a knackered box rather than haviing a decent one to learn in is exactly that.

Agreed, but the decision as to if/when the gearbox is replaced was never mine to take. I could only do the same as any other driver and report it.

Lucy:
Just because hauliers send their experienced drivers out in it doesn’t mean it’s good enough for teaching, the two scenarios simply aren’t comparable.

AFAIK, there’s nothing in the DSA guidance one way or the other on that point. My own view is that worn syncros don’t make a vehicle legally unroadworthy. No matter how much thought I expend on this subject, I wouldn’t be able to come up with a convincing reason for refusing to take a candidate for tuition in a vehicle with a defective syncro.

Lucy:
If you read above, you’ll see that ROG says he does NOT teach DDC unnecessarily -

ROG:
I do not introduce anything extra into the basic DSA test training format unless the trainee needs it or would benefit greatly from it.
If a trainee can go from gear 2 to gear 1 without any problems then why confuse them with double-de-cluching or blipping the throttle - it would not make sense

I agree with ROG and Mothertrucker.

Lucy:
That would kind of hint that it is NOT in the syllabus - and why should it be? This is 2007, not 1987, and the chances of any driver encountering a constant mesh box under any circumstances (other than as AMT, which is a whole other kettle of fish and also doesn’t need teaching at test) is pretty minute and getting more so by the day.

Whether it’s in the syllabus or not doesn’t alter the fact that most training school vehicles don’t have a syncro on first gear, or have “tired” gearboxes in general. If that were the case, IMHO I’d be remiss if I didn’t teach DDC to some extent.

Lucy:
It is perfectly reasonable these days for a driver unfamiliar with such a box to be given a “crash course” (pardon the pun) upon encountering one…

Therein lies the instructors’ dilemma. Our newbie might not be able to find an old hand if they “encountered one” on an early start. I’d also doubt whether that fault would be initially identified in the yard.

Lucy:
…there is simply NO need WHATSOEVER to teach it across the board!

Agreed, subject to caveats in this post.

Lucy:
As for the nitpicking over whether or not DDC damages synchros,

I wasn’t the one who said it did. I simply stated what I could remember from technical college, but it seems that people more qualified than myself agree. I’d be the first to say that my qualification in that area is probably so old as to be irrelevant.

Lucy:
suffice to say that whatever words you dig out in an attempt to ensure that everyone is right,

I didn’t feel that it was as black-and-white as that. I felt that several people had valid points, without being entirely wrong or right. I include myself in that, which was my reason for attempting a form of words.

Lucy:
and no matter how you dress it up, DDC a synchro will cause damage, by whatever means you wish to use to describe it.

I still say that it’s mis-matched shaft speeds that damage syncros when a driver uses force to overcome the resistance. Pray tell how simply operating a clutch pedal, even 20 times, will damage a syncro??

I also agree with skorpio since:

skorpio:
as a fully qualified technician, of too many years to admit

I believe that that opinion carries both weight and credibility.

As ever, I’m always prepared to be (proved) wrong, so I’m perfectly happy to wait for your reseach to provide another explanation.
As long as it comes from suitably qualified people, I’ll be bound by it. Will you?