Ok, question form a newbie.
In a Scania if your in 8th gear, does the box have built in protection to stop you from selecting low range and going in to 4th inadvertently. I’ve searched the net for info, and the trucks I’ve been in don’t seem to have an instruction manual.
Gordy
It should do yes. First time on a scania was a balls up for me because it would not go into low range when I wanted it to, having to wait till the speed was low enough (which felt too low to me)
Volvo gearboxes also stop you from doing it a too high speed.
I dont think the slap across boxes do though.
I think I’m right in saying that ALL gearboxes have interlinks to inhibit you from selecting too low a gear for the road speed that the vehicle is travelling at, and so preventing a blown engine and/or a sack of cogs being deposited on the road.
I use the term inhibit because Con & Use Regs require that lower gears must be able to be selected.
Always remember. If you can’t select a gear, more than likely it is YOU that is trying to do something wrong, rather than the vehicle behaving awkwardly. 
Thats what I thought as well Krankee. I din’t want to post it though, in case I was wrong and led someone up the garden path .
Its so long since I drove a slap-through range change, that I couldn’t be sure one way or the other.
Drove my 1st slap thru today, Iveco, must admit I found it easier than the Scania. Worked for a Bakery in Glasgow doing a few local jobs so plenty of gear changing.
Gordy