If you happen to forget you was in high range-on a manual box and reverse is this likely to damage the gearbox?
Not to the 'box, but a fair chance of damage to anything behind you. 
Reason I ask is, we’ve had a gearbox split it’s casing today and the garage have said it’s because the driver reversed in high range?!
Just wondering if there’s any truth in it or they are trying to get out of paying for it?
What gearbox? Sounds like they’re taking the ■■■■, to me.
Scania 4 over 4
Can’t see how they can prove it either way really?
Sounds like a made-up reason to me.
Unless they can explain exactly how that can split a casing, I wouldn’t believe it.
Seems to me like the only extra stress on the drivetrain would be the same as if you tried to pull away in too high a gear.
More likely to ruin the clutch, it was great fun reversing in high range, Lord knows what speed the old Fodens used to do in reverse in the highest of 3 ranges, same with the Eaton Twin, never known a gearbox break by doing this but then they weren’t Swedish boxes made of poncy cottage cheese.
One of my old mates split a David Brown 6 speed wide open, but that was because the PTO (driving rolonoff skip loader) was running off the wrong gear and if you went over 1000rpm it could load a skip in about 8 seconds flat, give it not enough throttle though and it would stall the engine which would then fire up and run backwards, miss those days 
Juddian:
More likely to ruin the clutch, it was great fun reversing in high range, Lord knows what speed the old Fodens used to do in reverse in the highest of 3 ranges, same with the Eaton Twin, never known a gearbox break by doing this but then they weren’t Swedish boxes made of poncy cottage cheese.One of my old mates split a David Brown 6 speed wide open, but that was because the PTO (driving rolonoff skip loader) was running off the wrong gear and if you went over 1000rpm it could load a skip in about 8 seconds flat, give it not enough throttle though and it would stall the engine which would then fire up and run backwards, miss those days
the twin splitter reverse in high split is not that fast but the 16 speed is neither here or there as in too low in low when straight reversing and too high in high .
tipperlad:
If you happen to forget you was in high range-on a manual box and reverse is this likely to damage the gearbox?
You’ll reverse faster than you were expecting. On most if not all gearboxes the split and range change can work in reverse too so you have 16 gears going forwards and 4 going back.
I don’t believe that reversing in high range would be harmful to anything but the clutch. However, if you started off reversing in low range, then changed range to high whilst the vehicle is moving, this can cause serious damage to certain types of gearboxes.
It didn’t bother the old Fullers, I did it plenty times, but some of the Scandy ones don’t like it at all.
Juddian:
More likely to ruin the clutch, it was great fun reversing in high range, Lord knows what speed the old Fodens used to do in reverse in the highest of 3 ranges, same with the Eaton Twin, never known a gearbox break by doing this but then they weren’t Swedish boxes made of poncy cottage cheese.One of my old mates split a David Brown 6 speed wide open, but that was because the PTO (driving rolonoff skip loader) was running off the wrong gear and if you went over 1000rpm it could load a skip in about 8 seconds flat, give it not enough throttle though and it would stall the engine which would then fire up and run backwards, miss those days
I tried it in high range with a 12 speed Foden eight legger. It was a fair old lick that you wouldn’t really want to do with an artic.
Sounds to me that low range has been selected at a speed far to high, yes I know the gearbox has an inhibitor to stop this happening but it’s easily possible in a Scania 4 over 4
Heard of this happening a few times, driven quite a few myself
Driving in high range and changing into high range, whilst reversing are two totally different scenarios.
I drive a manual scania and it has a sticker saying Gearbox will be damaged in high range reverse Or words to that effect . 
We only know what the garage have told him, we don’t know what actually happened!
I’m only pointing out it might not of happened in reverse at all, selecting low range at speed forwards can cause serious damages
tipperlad:
Scania 4 over 4
Can’t see how they can prove it either way really?
Many manual Scania gearboxes were reduced to scrap when being driven with a magnet on the tacho sender unit.
The range change inhibitor is controlled by a combination of a neutral sensor on the turret, and a speed signal from the tacho sender. If no signal is being received, then the range change, in some circumstances, will operate when the vehicle is travelling at high speed, with predictable results.
I Think, allegedly, so I’ve been told. Not that I would ever do such a thing!!