Melchett:
The clutch lives outside the gearbox, synchro lives inside
Correct
Melchett:
synchro can’t & doesn’t have any effect on the clutch, flywheel or engine speed
Correct
Melchett:
it (syncro) matches gear speeds within the gearbox to enable a smooth change.
Wrong, syncros enable gears to mesh without clashing when they’re syncronised, a seamless smooth change comes from the flywheel and clutch plate rotating at the same speed when they come together and drive is resumed 
coiler:
When I first bought an I shift in 2003 it was explained to me that there was no synchro in it, that along with an Ali casing meant it was about 200kg lighter than the 12 speed manual. I have had the 03, an 05 and an 08 gearbox apart for repairs and there is no synchro in them.
Although I may make the odd mistake I will not post facts on this forum which I either know are either untrue or which I know nothing about.
Was the old Volvo syncro box their own? as I believe the iShift is a ZF unit with Volvo software stirring the cogs, the very same box as fitted to DAF, Iveco etc but with a totally different outcome on its usefulness 
Big Joe:
Wrong, syncros enable gears to mesh without clashing when they’re syncronised, a seamless smooth change comes from the flywheel and clutch plate rotating at the same speed when they come together and drive is resumed
If that’s what you want to believe then fair play But you’ve moved the goalposts a little!
A lorry clutch should not be slipped, it should be in our out. That includes moving off from rest.
When changing down letting the clutch up without matching revs to road speed for the new gear, as CF has said, puts a great deal of strain on the drive line and synchro cones. Big Joe later tries hard to point this out.
OP you will soon give over with that method the first time your’e empty or light in the snow. (unless the exhaust brake is hooked into the ABS on these modern vehicles? I don’t know).
On downward changes revs should always be matched to road speed.
There has been a lot of talk about “blipping” the throttle. This is usually what’s done between gears when double declutching - in the case of a manual non synchro box.
(or by Scania V8 drivers who like to play “look at me”) 
With a synchro box, double declutching and blipping isn’t required, BUT when changing down, the revs should me matched to the road speed before letting the clutch up.
Big Joe:
a seamless smooth change comes from the flywheel and clutch plate rotating at the same speed when they come together and drive is resumed
Thats just about the whole principal of how a clutch is supposed to work. Infact once a clutch is fully released it does travel at the same speed as the flywheel. They where clever them guys that designed them eh ? 
Melchett:
Big Joe:
Wrong, syncros enable gears to mesh without clashing when they’re syncronised, a seamless smooth change comes from the flywheel and clutch plate rotating at the same speed when they come together and drive is resumedIf that’s what you want to believe then fair play
So if the gearbox input shaft is not connected to the flywheel as it isn’t when the clutch is disengaged, what difference does blipping the throttle make to the meshing of the gears? You need to reengage the clutch (double declutch) for it to have any effect whatsoever!!!
newmercman:
Blipping the throttle on a synchromesh gearbox will wear out the synchro rings faster than not blipping the throttle. If it’s synchromesh DO NOT BLIP!Automated Manual Transmissions, such as i-shift are constant mesh, this is why the computer blips the throttle on downshifts, or even applies the engine brake to get a fast upshift, it has to match engine and transmission speeds as there are no synchro rings.
Thats exactly as i understand it. The latter box (constant mesh) that would be in manual terms a “crash box” ?
I would not use the exhaust brake when empty …most are useless , and double de clutching is how it was allways before full syncro boxes were the norm, and blipping the revs as another op called it…was to speed the layshaft up to correct speed to accept the correct gear…and as an engine brake as such.even with a modern full sync box if your going too quick to change gear it will be just about impossible without doing damage by forcing it in at too high a speed.
newmercman:
Melchett:
Big Joe:
Wrong, syncros enable gears to mesh without clashing when they’re syncronised, a seamless smooth change comes from the flywheel and clutch plate rotating at the same speed when they come together and drive is resumedIf that’s what you want to believe then fair play
So if the gearbox input shaft is not connected to the flywheel as it isn’t when the clutch is disengaged, what difference does blipping the throttle make to the meshing of the gears? You need to reengage the clutch (double declutch) for it to have any effect whatsoever!!!
You need to seperate the aims of raising the engine speed to match the road speed to avoid the choice between clutch slip or excessive driveline stress on re engagement-
( because at that point we’re already in the new lower gear in which case the input shaft is now locked to the output shaft so the clutch centre plate is actually turning at whatever speed the gear multiplation is for the gear you’ve downshifted into relative to the road speed of the wheels ) ( IE the input shaft is not in an undriven state as it would be in neutral ) 
-from the aims of matching the roadspeed before making the actual downshift.
So just like with an unsychronised box the driver firstly needs to match the ‘roadspeed’ for the new lower gear before downshifting and the closer that match the easier it will be on the synchros and the layshaft and the input shaft.-
( If you don’t believe it the fact is it is actually possible to blow a synchro bag of bolts gearbox up with the clutch disengaged and therefore without it even being coupled to the engine and if you don’t believe that just drive your car up to 80 mph and then put it into first gear with the clutch disengaged and with the engine idling.Heres a clue the synchromesh will actually try to synchronise the gear and might even succeed.It’s what heppens next in either case which could get interesting while at no point has the clutch been connected to the engine). 
-‘Then’,having matched the road speed to the next gear down,the driver ‘secondly’ needs to raise the engine speed ‘before’ re engaging the clutch to synchronise the speed of the flywheel with the speed of the clutch plate which,as I’ve said,is ‘actually’ running at the speed of the output shaft multiplied by whatever the gear multiplication happens to be for the gear in question that you’ve downshifted into.Which of course avoids the choice between using excessive clutch slip or massive driveline loadings assuming you don’t bother when re engaging the clutch after the downshift.While it’s obvious in that case that,just like with a constant mesh box,it’s better to use a lot of close sequential downshifts than large block changes.
Then there’s the type of driver who just decides that it’s a lot faster and even easier on the driveline as a whole to just do all that together with double de clutching a synchro box.
Mike-C:
newmercman:
Blipping the throttle on a synchromesh gearbox will wear out the synchro rings faster than not blipping the throttle. If it’s synchromesh DO NOT BLIP!Automated Manual Transmissions, such as i-shift are constant mesh, this is why the computer blips the throttle on downshifts, or even applies the engine brake to get a fast upshift, it has to match engine and transmission speeds as there are no synchro rings.
Thats exactly as i understand it. The latter box (constant mesh) that would be in manual terms a “crash box” ?
A ‘crash box’ is actually a sliding mesh box not a constant mesh box.The common link between all three types sliding/constant/synchro is that synchronising of road and engine speeds is needed to drive them all properly it’s just that synchromesh will work without that synchronisation being as critical and without the need to synchronise the actual meshing of the gears in the same way as the other two types.
I’ve got an Eaton Fuller constant mesh in my current truck, after 800,000miles I’m still on the same clutch.
Before that I had a 143 with a 10spd and that never had clutch or synchro problems.
With the Fuller I match the revs, with the Scania I let the synchro do the job it’s designed to do.
It ain’t rocket science, so it doesn’t need overthinking!
Saaamon:
.I reckon this could well turn into 3 pages on whats the correct way to change gear…
You’ve been a bit optimistic - Just made Page 4
some of you need to the op’s original question:
Javiatrix:
Should I be matching the revs before clutching out? Or on these gearboxes is it fine, once off the gas, to simply clutch in, drop the gear, then clutch out, resulting in a large jump in revs
I think we’ve established the gearbox will be fine, whether it be syncronised, contant mesh, crash, dog gears, dogs bollox or whatever 
, but after the lower gear has been selected, the massive speed differential between the flywheel and clutch plate will result in some clutch plate wear and a certain amount of engine mount and driveline stress until they both syncronise and live on happily (not necessarily ever) after… until the next gearchange 
newmercman:
I’ve got an Eaton Fuller constant mesh in my current truck, after 800,000miles I’m still on the same clutch.Before that I had a 143 with a 10spd and that never had clutch or synchro problems.
With the Fuller I match the revs, with the Scania I let the synchro do the job it’s designed to do.
It ain’t rocket science, so it doesn’t need overthinking!
The whole issue really just shows the waste of time and expense which synchro boxes actually are.Effectively all they’ve done is to move the issue of having to match engine and road speeds further down the drive line chain.IE with a synchro instead of needing to synchronise the input shaft and output shaft speeds by raising the engine speed in neutral as in the case of a non synchro box you still need to do exactly the same thing except,in the case of a synchro box it’s synchronising the flywheel speed with the input shaft/clutch plate speed before re engagement.Unless that is you use clutch slip to lessen the effects on the drive line which just re engaging the clutch without doing so would cause.As you say it’s not rocket science.
I had given this up but…
Carryfast:
in the case of a synchro box it’s synchronising the flywheel speed with the input shaft/clutch plate speed before re engagement.
No it isn’t!
Synchromesh brings the selected gear up to the same speed as the input shaft gears to allow easy & noiseless changes, that’s all it does. It doesn’t (& can’t) affect the flywheel, the clutch, the brakes or the windscreen washers.
kemaro:
[zb] it , just slam it through the box up or down , I personally like to hold it flat to the very last minute then block from top to about 3rd, listen to it scream as it slows & the revs hit the red,clutch in , brake hard , hope the roundabout is clear then floor it through on the verge of tipping over , who gives a [zb] if it breaks , its not yours , your not paying , now that’s professional driving with a capital P!
I’m still right , my way is best , also sometimes I like to change gear without even using the cluth pedal , now that saves the clutch ( and my leg) a bit of wear & tear …4 pages on how to change gear …lol
Carryfast:
newmercman:
I’ve got an Eaton Fuller constant mesh in my current truck, after 800,000miles I’m still on the same clutch.Before that I had a 143 with a 10spd and that never had clutch or synchro problems.
With the Fuller I match the revs, with the Scania I let the synchro do the job it’s designed to do.
It ain’t rocket science, so it doesn’t need overthinking!
The whole issue really just shows the waste of time and expense which synchro boxes actually are.Effectively all they’ve done is to move the issue of having to match engine and road speeds further down the drive line chain.IE with a synchro instead of needing to synchronise the input shaft and output shaft speeds by raising the engine speed in neutral as in the case of a non synchro box you still need to do exactly the same thing except,in the case of a synchro box it’s synchronising the flywheel speed with the input shaft/clutch plate speed before re engagement.Unless that is you use clutch slip to lessen the effects on the drive line which just re engaging the clutch without doing so would cause.As you say it’s not rocket science.
It’s the dumbing down of the industry. Too many drivers lack the ability to change gear, it’s not a new phenomenon, it started in the 60s with synchro and has morphed into ATMs, some have taken that a step further and disabled all driver involvement beyond selecting forward or backwards…
To answer the OP, no you shouldn’t blip…unless you time it perfectly, you can cause the same wear by over blipping as you could by not blipping at all. As it is, the clutch has two functions, one being a device to allow a break in the drivetrain so that ratios can be changed, another is to act as a ‘shock absorber’ during those ratio changes and allow a smooth take up of drive they will wear out as a consequence of this.
Simples…
Melchett:
I had given this up but…Carryfast:
in the case of a synchro box it’s synchronising the flywheel speed with the input shaft/clutch plate speed before re engagement.No it isn’t!
Synchromesh brings the selected gear up to the same speed as the input shaft gears to allow easy & noiseless changes, that’s all it does. It doesn’t (& can’t) affect the flywheel, the clutch, the brakes or the windscreen washers.
Synchromesh actually synchronises the chosen gear with the ‘output’ shaft speed which is why,as I said,you can blow a synchro gearbox up by putting the thing into first gear at motorway speeds with the clutch disengaged and it’s also why,as I said,not matching the road speed properly before a downshift,or block changing as opposed to plenty of close sequential downshifts,will overload the synchros.
So you’re saying that the clutch centre plate isn’t connected to the input shaft and doesn’t turn at whatever speed the input shaft is turning at which,as I’ve said,would be the speed of the output shaft multiplied by the the amount of gear reduction,depending on which gear is selected during a downshift,before re engagement of the clutch centre plate with the flywheel.Assuming at that point the engine speed isn’t matched exactly to the increased speed of the clutch centre plate,by increasing it using the accelerator,then the mis match between the slower flywheel speed and the faster clutch centre plate speed will inevitably result in either stress being put through the driveline or slipping the clutch by engaging it slowly to avoid it. 
The fact is all that synchro boxes are just an expensive way to allow zb driving to go unheard.
Carryfast:
Melchett:
I had given this up but…Carryfast:
in the case of a synchro box it’s synchronising the flywheel speed with the input shaft/clutch plate speed before re engagement.No it isn’t!
Synchromesh brings the selected gear up to the same speed as the input shaft gears to allow easy & noiseless changes, that’s all it does. It doesn’t (& can’t) affect the flywheel, the clutch, the brakes or the windscreen washers.
Synchromesh actually synchronises the chosen gear with the ‘output’ shaft speed which is why,as I said,you can blow a synchro gearbox up by putting the thing into first gear at motorway speeds with the clutch disengaged and it’s also why,as I said,not matching the road speed properly before a downshift,or block changing as opposed to plenty of close sequential downshifts,will overload the synchros.
So you’re saying that the clutch centre plate isn’t connected to the input shaft and doesn’t turn at whatever speed the input shaft is turning at which,as I’ve said,would be the speed of the output shaft multiplied by the the amount of gear reduction,depending on which gear is selected during a downshift,before re engagement of the clutch centre plate with the flywheel.Assuming at that point the engine speed isn’t matched exactly to the increased speed of the clutch centre plate,by increasing it using the accelerator,then the mis match between the slower flywheel speed and the faster clutch centre plate speed will inevitably result in either stress being put through the driveline or slipping the clutch by engaging it slowly to avoid it.
The fact is all that synchro boxes are just an expensive way to allow zb driving to go unheard.
Speechless
kemaro:
kemaro:
[zb] it , just slam it through the box up or down , I personally like to hold it flat to the very last minute then block from top to about 3rd, listen to it scream as it slows & the revs hit the red,clutch in , brake hard , hope the roundabout is clear then floor it through on the verge of tipping over , who gives a [zb] if it breaks , its not yours , your not paying , now that’s professional driving with a capital P!I’m still right , my way is best , also sometimes I like to change gear without even using the cluth pedal , now that saves the clutch ( and my leg) a bit of wear & tear …4 pages on how to change gear …lol
correct your not paying, and if it is covered by warranty they won’t be paying either ,as it will be rejected due to DRIVER abuse,so it will be down to your not so happy boss…Tell tale signs ,blueing of the bulk ring ,or broken bulk rings,to name but 2 obvious signs of abuse