The good old mid lift axle, there are minor differences to how each maker’s mid lifts behave, and now and again you might come across an aftermarket that is different again (fortunately rare).
This is for mid lifts, rear tag axles are rare and i’ll leave those to someone more experienced than i am.
Yes empty up and loaded down, but if lightly loaded run with it up, you’ll find handling better and wet grip miles better.
As a general rule if the mid lift is an auto and has stayed up when loaded then the tractor is lightly enough loaded to continue like that, once empty if might come up on its own but other makes will not, ■■■■ it and see.
Older Axors are an exception here, one of the few lorries with a full size mid lift that the driver has total control over, the mid lift will come up if the button is pressed (on ones i’ve driven) fully loaded so care is needed, but these vehicles are birlliant for hill climbing in the snow because you can get that axle up long before the speed limit override on other makes allows this, older Axor is one of the most modern old school driver’s lorries about and will laugh at snow that other makes will leave you stranded in.
Haven’t driven a new shape Axor or Actros so can’t tell you if the above still applies you’ll have to try it and see if you have one.
Anyway back to general mid lifts.
There are normally two buttons on the dash for controls, one with the umbrella over the axle on the switch is the air dump valve, this is for transferring the weight off a loaded mid lift for traction purposes (some mid lifts will lift completely off the ground during use if you have full air, MAN’s in particular), it doesn’t usually work over 20mph hence on snow/ice hill climbing you will need to test at what speed it starts to work so you can dump the air as early as possible as you climb a slippery hill to give you a fighting chance of making the hill.
I use the dump control when loaded off the public highway all the time, it cuts down on tyre scrub and lessens wear on all the mid lift bushes, also makes manoeuvering easier because the vehicle turns easier, i will also dump the mid lift air temporarily when pulling out of a slippery junction cos it lessens the chance of wheelspin…with MAN’s definately and older Axors as previously said (others can’t remember/don’t know) the mid lift will riase off the ground after about 10 seconds or so even fully loaded if you full air pressure, but on MAN’s will normally drop again once up to 20 mph but on the open road you would drop it again manually once the danger of a slippery junction was passed…i wouldn’t like to say the legal implications of this but it would an unusual VOSA man who had a go at you for ensuring you had a safe junction exit for a moment by transferring weight onto the drive axle.
If any VOSA/DVSA whatever its called this week staff happen to read this i’d welcome any comments about this practice please re legalities and how you view such things.
Now this is where it gets interesting, cos sometimes even with the mid lift air dumped as soon as the vehicle detects the slightest wheelspin the traction control will cut the power, this is a pain in the arse if you’re cursed with any of the unfit for purpose Arsetronic boxes now de rigeur, so if you have that nasty jack knife reverse uphill on a slippery slope as well as dumping the mid lift air it might pay to switch off TC or ASR (MANs version of TC) this will allow a drive wheel to slip without cutting the power and releasing the clutch as it does on arstronic…learn this technique because it will get you out of slippery situations in the winter…and whilst on winter diff lock can be a boon it can make things worse too, sometimes with both wheels spinning the drive axle will slip sideways depending on camber, sometimes leaving diff lock off allows one wheel to spin and dig down to tarmac, other times teh diff lock get you going and through, no two situations will be the same and learning exactly how your own lorry behaves before the snow arrives is vital.
The switch with the umbrella is only meant for dumping the air, it is not the lift/lower control, and as soon as you get up to speed (20mph ish) the mid lift will drop back down again (usually), so when you get up to about 30mph when emptyish have quick glance down and check the amber lift light is still lit, its too easy to hit the umbrella button instead of the raise lower button, then you end up with the vehicle skittish as hell and you wonder why till you finally stop and then see the mid lift was down empty.
Some mid lift raise lower buttons are a bit finicky and in the most stupid places, MAN i’m looking at you here with your idiotic VW inspired red back lighting which can’t bee seen properly where you sited the switches, and you’ll have to have a play with the raise lower to see exactly how it works and when, there are no hard and fast rules here.
Generally (Axor excepted, there may be others) once over a certain weight the up/down button will not function so its dump valve only.
I also recall my Volvo FM’s automatically raising the axle once unloaded, but only after switching off and restarting, but these were aftermarket mid lifts which were never correctly switched in the first place and had to be retrofitted with dump valves…a story for another day…how normal Volvo’s behave now i haven’t a clue.
There’s probably lots more i haven’t covered but thats enough waffle for now.
and who rattled Evil’s bleedin cage anyhow 
makes a lot of sense, in all honesty most trainers if they’ve been training a long time won’t have had recent years of on the job practice of things like the idionsyncracies of and how to get the best out of lift axles, diff locks and things, due to the type of driving they are involved in.