The cones are only coming into contact when the speeds are matched when you DDC. Otherwise that is what they are there for. If you DDC there is little or no wear on the syncro as there is no speed differential. If you do not DDC then the syncro does its job and will obviously wear.
As regards clutch speeds/wear the syncro has nothing to do with it… When you change down a gear the engine speed and the road wheel speed need to be matched. All the syncro does is match the speeds of the shafts/cogs in the gearbox to enable them to mesh more easily. If the clutch is depressed then the engine speed does nt affect what is going on in the gearbox. DDC or blipping the throttle will match those speeds and reduce wear on the clutch plate.
This is getting like the plane on a conveyor belt thread a while ago. Simple physics is the answer.
I dont think you should teach DDC. Its not tested therefore dont teach it.
You dont learn to “drive” the wagon you learn to pass the test. If you were learning to drive the wagon you would be tested on:
blindside reversing
suspension ride heights
loading
roping and sheeting
fridge controls
There is more to driving than what is covered on the test and before you start teaching the art of DDC there are lots more things that you are more likley to need to use before DDC!!!
I can guesss that the people that want DDC are the same people that have done DDC since thier car needed it. For those of us that started to drive when cars had power steering as standard you can expect that we would need to learn it just for the truck test.
In any case I think it was the Merc that I was driving last week DDCd for you. When changing down it blipped the throttle to bring the revs up for you. Now that was a nice drive.
Here’s my two pen’worth.I learned to drive in the army in 1962.We started on Morris Commercial 1 tonners and they had the most evil “crash” box you could ever imagine.After,and only after,you had mastered that,we went on to the vehicle we were to drive for our daily job,in my case,it was the “Saladin” armoured car,with a Wison pre select 'box.I eventually became an instructor on these,then moved onto “Chieftain” tanks,6 speed semi auto.
In those days,very few cars had an all synchro box,(or if they had it was so worn it may as well not have had)so DDC was the rule rather than the exception.
Now in my retirement,I do two nights a week trunking with an Axor,4 over 4.synchro of course.
After two years on this,the office decided I had not had a driving assessment when I started,would I mind going out for half an hour with one of the companies driving instructors.
We went out around the town and on our return the only real comment by the instructor was,“These trucks are extremely economical on fuel,and I think that revving up the engine when changing down,(irrespective of DDC or not) is wasteful”.
Now I have done more miles in car parks than this instructor has done,but fair do’s,it’s his job and he’s got to have his say.
Now,as has been mentioned earlier in this thread,when I taught driving in the army,the mechanics of the INSIDE of the engine,gearbox and any other transmission part,were taught,so the student knew exactly what was happening every time he revved the engine or depressed the clutch.
So,in todays trucks with their synchro transmissions,is DDC or revving up as you change down really necessary?
I think that revving up to match the engine speed to road speed for a lower gear,is more cost effective than pushing the gearlever straight through and slipping the clutch to take up the drive again.
How many miles do you have to drive before you have saved enough fuel to replace the clutch?
In all my driving career,I have never had a clutch replaced in a truck,or car,that I have been driving.
Now we have some ERF/MAN tractors with Servoshift.Now they rev up automatically when you change down,eeeerrrrrmmmm?
I rest my case!
I’m no expert and I have never really ‘needed’ to DDC although I do know how to do it.
I was also told during my LGV lessons etc that some people/examiners complain about blipping the throttle when changing gear as it ‘wastes fuel’ and some thought it helped.
I find that in most vehicles, say when changing down the engine revs can drop to idle speed if you don’t make a quick change. Then the weight of the vehicle has got to bring the revs back up when the clutch is brought out. Blipping obviously helps as it is easier for the engine to slow than it is to speed up.
I think the little extra fuel it does use when blipping is greatly out weighed by the savings in terms of wear to clutches, gearboxes etc. After all the engine is supposed to be doing those revs at that speed. Take an auto for instance, you don’t see the revs dropping do you? Plus it is a smoother ride without the nodding.
Sorry for the rushed message, hope it makes sense.
Now that may well be the answer to all of this. Correct and effective DDC takes time to master, certainly more than 5 days in a synchro’d vehicle…hence attempting to teach newbies in this way is a bad move. It would also explain why so many of us have been warned off it on the grounds of “gearbox damage”.
When i was training for my then, class 1, I had to learn it bloody quick and had it mastered in 2 days , as did the other trainees at the time.
It also meant that I drove my car by DDC whilst training- oh well
Wow, some thread.
I wouldn’t have a clue what the inside of a gearbox looks like, although I did once strip, clean and re-assemble the transfer box on my wartime Morris Commercial 4wd recker using the (obviously) idiot -proof 1944 army workshop manual for (every) step by (every) step instruction.
But, double de-clutching (didn’t know it was called DDC 'till today ) was always the norm for me and as far as I remember I still used it on my last wagon. I do know though that I have always used it for downshifting with the accompanying throttle blip and still do even on my car. The reason is to match the road speed to the engine speed and therefore avoid a sudden reduction in the former which could otherwise induce a skid.
Surprised no-one mentioned that. That was the reason given by the bloke who showed me how to drive my very first vehicle, a BSA 250 C12, to avoid ending in a pile in the ditch.
Still holds good today IMHO.
Decided to practice some DDC at work tonight. I dont know what it was but I smelt burning.
Now if the costs of breaking stuff learning DDC are taken into account does that make it more economical?
I think you need to be taught to DDC properly, rather than just practice
I was taught by my father who learnt to drive with non synchro ‘crash’ boxes, then spent his war years driving a Quad with limber and 25pounder, it is second nature to me, and personally feel it results in a smoother shift, this, IMHO, would indicate less wear taking place, even to those who don’t understand what is going on inside the 'box
This link - singster.co.uk/mascot%20mar-apr%202003%20(4.html - gives a good explanation of how a synchro works, he also agrees with Lucy in so far as he says DDCing will damage the the synchro rings but doesn’t say why
As I said previously I spent a good few years in the w/shops when g/boxes were rebuilt as a matter of course, and am v. well qualified on them [should have a big head smiley ] then had to give up as my back problem was getting worse so now drive them instead
I have looked around and cannot find any factual evidence that can either point towards, let alone prove that DDCing will damage a 'box in any way. The simple act of shaft speed matching will reduce wear rather than increase it. I feel that the subject will go around in circles for ever though as there is divided opinion even amongst those that do know what is going on inside the 'box, I spoke to a couple of mechanics yesterday - in a large haulage company (N. Wales with orange and cream colour scheme ) next to our yard - both experienced on heavy stuff, each had a differant opinion on the matter, I think I’ve started an argument there now
But it’s healthy to discuss issues even if we’ll never resolve them me, I’ll continue to DDC, others will not. ( I still feel it’s too much to teach on top of how to drive the things for test, it’s just something else to mess up on and fail )
That’s is what is intriguing me so much now. Despite all logical explanations to the contrary, there still seem to be a huge number of experienced mechanics who will tell you that DDC-ing a synchro damages it …but no-one as yet who can give us details as to how.
I’ve gone so far from being of the “will definately damage” school of thought to “unsure”, a state of affairs which is not helped by examples like mine and Skorpio’s above where two senior mechanics have been left at loggerheads.
I guess we just have keep on plugging away at this one until one of the “naysayers” (as in “nay” to DDC, rather than “nay” to damage) can actually come up with an explanation. Great link, btw Skorpio - I shall pore over that at my leisure later on.
Lucy:
That’s is what is intriguing me so much now. Despite all logical explanations to the contrary, there still seem to be a huge number of experienced mechanics who will tell you that DDC-ing a synchro damages it …but no-one as yet who can give us details as to how.
Because it doesn’t, it can’t and they are wrong
Lucy:
I’ve gone so far from being of the “will definately damage” school of thought to “unsure”, a state of affairs which is not helped by examples like mine and Skorpio’s above where two senior mechanics have been left at loggerheads.
Perhaps they are mechanics but not engineers (not wishing to cast doubt on anyone I haven’t met.)
Lucy:
I guess we just have keep on plugging away at this one until one of the “naysayers” (as in “nay” to DDC, rather than “nay” to damage) can actually come up with an explanation. …
Which they won’t because it doesn’t. The only time that there could be any wear is when the clutch is engaged. Since this happens when the gearbox is in nuetral (when DDCing) there can be no friction imposed on any of the syncro components. Hence no wear is possible. Unless being in nuetral with the clutch engaged is going to cause wear…■■
When the evidence is so clear there can be no justice in this world if the jury decide that DDC is bad from that point of view
Hey, give me a break, I’m making the effort here! And heading in the right direction! And Expert 1 is, in fact, an Engineer, if you wish to be picky about such things.
Lucy:
That’s is what is intriguing me so much now. Despite all logical explanations to the contrary, there still seem to be a huge number of experienced mechanics who will tell you that DDC-ing a synchro damages it …but no-one as yet who can give us details as to how.
Because it doesn’t, it can’t and they are wrong
Lucy:
I’ve gone so far from being of the “will definately damage” school of thought to “unsure”, a state of affairs which is not helped by examples like mine and Skorpio’s above where two senior mechanics have been left at loggerheads.
Perhaps they are mechanics but not engineers (not wishing to cast doubt on anyone I haven’t met.)
Lucy:
I guess we just have keep on plugging away at this one until one of the “naysayers” (as in “nay” to DDC, rather than “nay” to damage) can actually come up with an explanation. …
Which they won’t because it doesn’t. The only time that there could be any wear is when the clutch is engaged. Since this happens when the gearbox is in nuetral (when DDCing) there can be no friction imposed on any of the syncro components. Hence no wear is possible. Unless being in nuetral with the clutch engaged is going to cause wear…■■
When the evidence is so clear there can be no justice in this world if the jury decide that DDC is bad from that point of view
Nah…I’m enjoying myself. Even if I eventually prove to my own satisfaction that those who have been telling me DDC-ing does damage were wrong, I’ll have had a great deal of amusement in getting there.
I’ve read most of the thread, and even understood some of it…
Can’t believe any technician would agree that double de-clutching would prematurely wear out a gearbox…
Yes everyone should be taught it from the off. It doesn’t take five days, and like anything else, it’s only difficult until you know how to do it. Like riding a bike, once you know how, it never leaves you. Much better and easier to learn when you start out than later on.
It certainly helps when you’ve got a tired box, and, more importantly, helps you to have a better understanding of what your engine and gearbox are actually doing. I don’t always use it, but can when I want/need to. And as others have said, almost always blip the throttle when coming down the box. Again, I think when you have a slight understanding of the mechanical process, you tend to be a little more sympathetic in your driving habits…which in my opinion reduces wear and tear. It actually makes me wince to hear the way some people drive. ( But then some would say I am a little odd…)
Although I already had a car licence, when taking my class three in the Army (1986) , we had to DDC, even though we didn’t need to. My particular instructor had one of those collapsible car radio aerials, (often used as pointers when in the classroom) and whenever a DDC wasn’t correctly performed - or anything else for that matter - a swift rap across the knuckles followed with aforementioned implement. I found I mastered it quite quickly… Similarly when passing my class one a couple of years later, DDC was required even though ever less relevant.
As a proffesional driver, it’s something you should want to know how to do.
Although not directly comparable, it’s a bit like learning to add up on a calculator, or learning to navigate with a Tom-Tom, all fine and dandy until the batteries have run out etc.
Following my earlier post on being assessed and told about the “wasteful” use of fuel by revving up as you change down,I don’t know what comments were made to drivers who STILL start off when loaded,halfway up the 'box and slip the clutch to get moving!
These are the same drivers who REALLY make the synchros work for a living by snatching through every gear,resulting in the truck rearing up every time they let the clutch out again.
Wasteful use of fuel?I think not!
It makes me cringe when I have to go double manned to be paired with a numpty.When I’ve mentioned my assessment,I’ve had one driver say to me"Well,you always drive better when being asessed don’t you?"
Can you believe this?
Now you know why owner drivers prefer to stay owner drivers as the biggest gamble they take is setting on a second driver.
Anyone that’s learned to drive in the military will tell you,that’s what is drilled into you constantly,drive sympathetically to get the best out of the vehicle for as long as possible,you don’t want it to let you down at the wrong time!
Pop Larkin:
I guess beleaguered students would have to find the same time as before. I had to learn DDC because until you had learned to, you couldn’t change gear unless you had one of those new-fangled F86’s or F88’s.
My guess is that it isn’t DDC that damages gearboxes, it is poor DDC that does. Learning to DDC on synchro boxes masks any defiency in technique - I’ve seen loads of drivers DDC, or think they have when in reality they’ve done nothing more than dip the clutch with an arbitary blip of throttle. There’s more to DDC than that if everything is to be matched up.
I’m not picking this apart, because I believe every word of it. It’s also very well put.
Pop Larkin:
As for pressure of training costs? That’s a joke. Training is cheaper today than it’s ever been! OK, it’s still a sizeable chunk of cash, but when I learnt it cost me £175, and that was when earning £30.00 a week was top money, between £20 and £25.00 was more normal, £50 would buy a good car and it would cost £35 a year to insure it, and for the current price of a pint you could get well lashed and still have change. At the time I was running my own Transit, charging 11.5p per mile and making enough I could afford my HGV licence. Had I been working for somebody, the £175 would have been as far away as a mortgage is to first time buyers today.
First point: economics isn’t my “thing.” My gut reaction seems to tell me that training to Cat C+E is far more expensive now, because of the requirement to do Cat C first. When I did my training in 1979, it was possible to do C+E straight off (without even a car licence that was called double “L”, because you would have had both types of “L” plate on an artic ) I did my training with BSM and it cost £480 for a 5-day course. I’m going no further with “training costs” it might be “off-topic” and needing another split
Pop Larkin:
And if anybody accuses me of being old - they are likely right, or do I just feel it!
They can say the same to me and then get bored, cos I’d just agree (only cos they’d be right )
Lucy:
That’s is what is intriguing me so much now. Despite all logical explanations to the contrary, there still seem to be a huge number of experienced mechanics who will tell you that DDC-ing a synchro damages it …but no-one as yet who can give us details as to how.
I haven’t counted the responses to see if the “huge number of mechanics” claiming DDC will cause damage is greater then those who don’t think it can. even if they do it’s interesting to note that all those who think it won’t do any harm can explain their theory in detail. So far not one of the other camp has been able to explain how the damage is done.
Gardun:
Perhaps they are mechanics but not engineers (not wishing to cast doubt on anyone I haven’t met.)
Good point. It’s quite possible to follow the manual and repair a gearbox (or anything) without needing to understand how it works.
neil4967:
I don’t always use it, but can when I want/need to. And as others have said, almost always blip the throttle when coming down the box.
Likewise, I’m prepared to accept that DDC could cost more in fuel than it saves on synchro wear but can’t understand the sense of NOT blipping the throttle. Allowing the clutch to do the job of accelerating a big diesel engine can’t be good for it’s life expectancy and the constant snatching from drive/overrun this must induce is putting undue stress on the entire drivetrain.
Sockpuppet:
Decided to practice some DDC at work tonight. I dont know what it was but I smelt burning.
LOL. How the hell did you manage that? Somewhere in this thread I’ve admitted that bad technique could increase wear but I was thinking long term. Even if you were practicing clutchless changes (don’t try until you’ve mastered DDC!) and leaning on the gear lever with all your weight I doubt you’d generate enough friction to boil the oil!
) was always the norm for me and as far as I remember I still used it on my last wagon. I do know though that I have always used it for downshifting with the accompanying throttle blip and still do even on my car. The reason is to match the road speed to the engine speed and therefore avoid a sudden reduction in the former which could otherwise induce a skid.
so now drive them instead 
)