My understanding was that eaton are not saying DDC damages the synchro because drivers get the revs wrong but because they’e accidentally engaging the next gear with the clutch pedal up because they’re trying to rush the change and move the lever in one movement, rather than pausing in the middle?
Agreed, that could do some harm but as pop says drivers who don’t DDC still do this. I remember being taught to tap the lever to the side as a sort of dummy change (not a slap over!) to slow me down.
Rikki, I like your point about missing a gear. Whenever I’ve done that I’ve lost the rhythm and been unable to find any gear to keep going or even work out which one I could catch next! Hills are certainly a lot less scary with synchromesh.
Rikki-UK:
Seeing as how this debate has taken many twists and turns I thought I would ask our friends at EATON transmissions
Do your friends have anything to do with the Eaton transmission engineering department in Farnworth, Bolton?
I remember one of my favourite jobs with the agency was “test driving” an Eaton Twin Splitter in a 190.42 Turbostar loaded with ballast to 44 tonnes (with special dispensation from the DoT).
We had to follow a fixed test route that crossed and re-crossed the Pennines and occasionally had to do stuff like record the maximum gearbox oil temperature, but basically the job was just endurance testing; putting miles on the gearbox.
The guy in charge of the project (I’m thinking hard now, this was YEARS ago, late 1980’s… was it Steve something??) had only one rule - no chocolate in the cab!
The first time out the 4x3 nature of the gearbox was a bit confusing but I soon got the hang of skip shifting up two gears at a time - up to the next gear with the lever and down two on the splitter (or up one, if in middle or bottom split) and of course the same in reverse for going down the box. I was told it was a ‘thinking persons gearbox’ I seem to remember too that it was easy to make clutchless changes that way and the clutch was then needed just for starting and stopping. I have a feeling that we were encouraged to do it that way too - but that was then and under specific conditions, so don’t take that as gospel. It is about 20 years ago too so I may have mis-remembered.
Somewhere I have a photograph of that Turbostar - I’ll have to try and dig it out!
Only just read this reply from Eaton. What the reply seems to have missed is that in a correct DDC you will (if going down the box) blip the throttle to raise and match the engine (input shaft) speed whilst the lever is in neutral and the clutch engaged and then move to the next gear with the clutch disengaged. In a correct DDC there will be no wear on the synchro, only if it is incorrectly or badly executed.
When DDCing it is important not to rush (ie do not move the gear lever until the clutch is disengaged) so the idea that you start to move the lever before the clutch is completely disengaged refers to bad practice.
Although the reply from Eaton is quite correct (and who am I to doubt them) it is not completely keeping to the original question.
Since my Actros has the EPS box I can’t DDC anyway
In a perfect world I dont suppose DDC will wear any thing out any faster but in a perfect world the main shaft would be spinning at the correct speed for the descent and the engine will be at the correct revs. All the cones and baulk rings are spinning at the correct speed and everything is ticketyboo.
However in the less than perfect world. when DDC is used on a synchro box you are just adding other things to either go wrong (ie wear out)
At least Eaton agree with me that premature wear will occur by bad DDC. Back to the perfect world and nothing will be damaged or worn out because the DDC was carried out correctly.
I worked for a bloke who told us not to use the red button on a 13 speed eaton fuller in an Iveco cos you will wear it out
I also have little faith in modern army training, especially as a bloke I worked with who would never make a lorry driver as long as he had a hole in his arse, was appointed senior civilian instructor at Leconfield.
I also disagree that synchro boxes are or ever have been quicker to change than a constant mesh gearbox in the right hands.
Rikki-UK:
Seeing as how this debate has taken many twists and turns I thought I would ask our friends at EATON transmissions … and here is the definative reply
Interesting conversation. No doubt a subject of debate and in need of
clarification, let me see if I can make sense of this for everyone.
Lets start with the purpose of the synchronizer. The synchronizer is
intended to bring the main shaft gearing up to speed with the main shaft
allowing smooth engagement of the clutching teeth, which will transmit
torque thru that gear. The main shaft will always be spinning at the
road speed of the truck. When the master clutch is disengaged (pushed
to the floor) the engine is disconnected from the transmission allowing
the synchronizer to do it’s job. In the 1.5 seconds it takes the driver
to move the lever to the next position all of this is happening. This
is a little summary of what happens mechanically during a shift, now
let’s clarify the debate if double clutching damages synchronizers.
Let’s think about the shift using the double clutch method. Your driving
down the road in 6th gear, you see a red light ahead and you begin to
slow down. You want to use the engine to slow you down, so you depress
the clutch, move the lever to neutral, re-engage the clutch, and begin
disengaging the clutch again while moving the lever into 5th gear.
Right? Remember this, when you begin disengaging the clutch with your
foot it takes a certain amount of time for total disengagement and speed
differential between the input shaft and engine to occur. In most cases
when a driver begins depressing the clutch for the second time he
already has the lever in motion to the next gear, pushing up against the
synchronizer, before the clutch has totally disengaged. What does this
mean? It means the synchronizer is trying to match the engine to the
road speed. Guess what. Then engine RPM is not going to change and the
synchronizer is going to suffer. The synchronizer is only designed to
bring the input shaft and main shaft gearing up to speed with the main
shaft, it will not overcome the engine. Now, this may be a very quick
event and will not immediately destroy the synchronizer but it will
cause accelerated wear. Can a very patient driver use the double clutch
method without causing increased wear? Yes. But are we always this
conscious of our shifts? To be safe, single clutching is best for
synchronized transmissions.
Seems to me that the conclusion reached there is based on the erroneous idea that a double de clutched change on a synchro box is done differently to a constant mesh box.In fact double de clutching is made up of entirely seperate operations of de clutching,then shifting into neutral,then re engage clutch to synchronise the shaft/gear speeds,then de clutch the second time then shift into the next gear required.However a good driver can make all those seperate operations look like they’re all being done at once and that’s probably why Mr Eaton has got a bit confused.
I have wandered over to this part of the forum and came upon this thread, all very interesting to me as, some of you may have seen my posts in the Pro Drivers ‘crap drivers cant save fuel for toffee’ or wotever thread and i openly admitted, in front of our more ‘learned’ friends (Rob-K, BTD etc etc ) to DDC/blipping/clutchless gear changes and block changing up through the box only to be shot down in flames, being told it was all wrong and it will all break blah blah blah. Reading this gives me more hope…or does it?
I seem to remember too that it was easy to make clutchless changes that way and the clutch was then needed just for starting and stopping. I have a feeling that we were encouraged to do it that way too - but that was then and under specific conditions, so don’t take that as gospel. It is about 20 years ago too so I may have mis-remembered.
