Wozzer:
The truck was a V registered ERF !
OMG, the gearbox, I couldnât seem to go anywhere in it until a chap in the yard took me around the yard in it and demonstrated it. For the oldies here it was an Eaton 12 speed box with 1,4,7 and 10 on the main stick and all the others on the sliding switch on the side of the knob.
Hi wozzer, I canât help but agree with Peterâs post above, including the part about it maybe being confusing. 
Iâd suggest that the easiest way to imagine the positions for the gears is to first remember an old-fashioned four-speed gearbox as fitted to cars.
Now imagine that each of the four gear slots in the âHâ gate has three available gears instead of one, so thatâs how you get to having 12 gears altogether.
Just for the discussion, letâs start by saying that on this occasion you need to use all 12 gears, so now weâll see how to use them in the correct orderâŚ
Select the âlowâ position on the splitter switch, and using the clutch in the normal way, select 1st gear in the âHâ gate, then set off⌠(You wonât now need your left foot for the rest of this procedure. )
Whilst youâre moving, select the middle position on the splitter switch, lift your right foot very slightly of the gas pedal, then slightly depress your right foot. Youâll now be in second gearâŚ
Repeat the step above after selecting âhighâ split, then youâll be in third gearâŚ
To get 4th gear, move the splitter selector back to the âlowâ position, ease off the gas as above, then move the gearstick itself to what youâd imagine is the second gear position in the âHâ gate.
The rest of the gears are found and used in exactly the way Iâve described above.
As Peter mentioned, in reality, you can do âskipâ changes dependent on the gradient of the road and the weight of the load.
Changing down through the gears requires little âblipsâ of the throttle, but you must remember that, if youâre âskipâ changing downwards⌠the bigger the skip = the bigger the throttle âblipâ needed. (Yes, sometimes a âbootful.â )
It doesnât matter who you are, everybody has to learn at some point and everybody had a âfirst dayâ, so please donât be too embarassed by the tunes youâll inevitably be playing as you master the art of driving a twin-splitter.
Itâs all a question of matching your road speed (MPH) to the engine speed (RPM,) so the only difference is that youâre physically managing the function provided by the synchros of a more ânormalâ manual gearbox.
Once youâve mastered the above, youâll find that the Eaton twin-splitter is actually a very good gearbox, and pretty straightforward to drive.
The gear position marked âCâ is for âcrawlerâ gear, which is a gear thatâs even lower that 1st âlowâ and doesnât split. You wonât normally need to even consider using this gear.
TIP #1
To avoid embarassing crunching noises when selecting whatever gear you decide to use for setting-off, depress the clutch pedal all the way to the end, then just as youâre selecting the gear, push the clutch pedal (quite hard) an extra half inch. This will operate the transmission brake, which slows the gear shafts sufficiently so as to match engine speed (tickover RPM) with road speed (0 MPH) Itâll always crunch if you donât.
TIP #2
Select reverse gear with care, cos there are three of them, depending on the position of the splitter switch. 
WARNING: You can use three reverse gears one after the other as described above, but if you try it, PLEASE be careful, cos reverse âhighâ is pretty quick.
I hope that helps. 
