I have heard drivers talking about extending and shortening their skellies using air lines instead of a valve. Can anyone explain how to do this?
You have two red line connections on the skellie. The main red line connection is usually mingled in with the others, just like on a normal trailer, but the second red line connection is usually separate from them, but still easy to find.
It’s a simple case of applying handbrake, climbing up on the cat walk, taking the red line off its normal running connection and putting it on the other one which will release the locking pins down the inside of the skellie chassis. This then enables the two parts of skellie to slide freely inside each other and you move them about by getting back in the cab and either reversing or driving forward to shrink it or extend it. One it’s in position, you then get back up on the cat walk and swap the red line back again to normal driving connection.
Allus check that the pins have engaged in the chassis before moving off. If they haven’t then get back in the cab and take the hand brake off - this normally sorts them out and they engage (you’ll hear them). If that doesn’t work that gently rock the truck back and forth until they do.
Thanks, Rob 
how do you gently rock a 30t 20 footer 
alix776:
how do you gently rock a 30t 20 footer
“By carefull & co-ordinated use of clutch, gears, brake and accelerator.”
Can you tell what i’ve been doing for the last few weeks? 
very true ive been doing the same
alix776:
how do you gently rock a 30t 20 footer
Yeah, if it’s a heavy box then you might need to ‘toe it’ a bit .
marcustandy:
Can you tell what i’ve been doing for the last few weeks?
Answer = driver training 2 students on C+E!! (Both passed; one with 4 driving faults and the other (show-off!!) with only 1!!) 
marcustandy:
alix776:
how do you gently rock a 30t 20 footer“By carefull & co-ordinated use of clutch, gears, brake and accelerator.”
…and that is just instructor speak as per the DSA course.
Rob Ks pretty much covered it
but to add a few more details,you also have the laden lock position for 20’ boxes which are about a 300mm difference to full extend .when you have a loaded box put on a docks or have loaded somewhere, make sure the trailer is in the laden lock position for transporting.
so i would fully stretch trailer then back it off a little,swap the air line,then back it off a little,swap the air line again,put trailer brake on then reverse abit and the pins will lock into the laden position.
Just make sure that if you load somewhere for export and take it off at the docks and are having a 40’ put on after,make sure you fully stretch the trailer again.
(gets a bit embaressing when you have to get the straddler back to take the box off again because its not sitting on the right pins on the front of the trailer) 
Rob Ks pretty much covered it
but to add a few more details,you also have the laden lock position for 20’ boxes which are about a 300mm difference to full extend .when you have a loaded box put on a docks or have loaded somewhere, make sure the trailer is in the laden lock position for transporting.
so i would fully stretch trailer then back it off a little,swap the air line,put trailer brake on then reverse abit and the pins will lock into the laden position.
Just make sure that if you load somewhere for export and take it off at the docks and are having a 40’ put on after,make sure you fully stretch the trailer again.
(gets a bit embaressing when you have to get the straddler back to take the box off again because its not sitting on the right pins on the front of the trailer)
Also when you stretch/shorten a loaded 20’ make sure trailer and unit are straight i.e before you reverse onto a bay/ramp make sure your alligned and then shorten trailer,dont try and drive round a yard with a loaded box on a short trailer as it will be extremely difficult to move or stretch it back again.
You’ ve been warned 
Its been said already, Rob Ks covered it pretty well. But, instead of trying to judge it just right, so that the pins drop into the locking holes when you release the air pressure. I would stop a bit short, on purpose, pull the red line off the locking pin connection and carefully lay it on the catwalk. Then move the rest of the way, the pins will go in with a bit of a bang, so you’ll know they’ve gone in. Then gently rock the truck back and forth, to be sure they have dropped right in. Then GOAL. If everything is looking good, back onto the catwalk and connect up to the normal running connection and away you go.
I’ve never worked with skellies, but I have hauled long steel sections on trombones, which are extended in much the same way, you just have a much greater choice of lengths.