Answers please.
Depends what way you go lol
The rear of the 5th wheel jaw (the sliding part) pulls the trailer along as the unit moves forward.
What makes you think it might push the trailer■■?
When you’re going forward the trailer is pulled, when you go in reverse the trailer is pushed.
If i put my pedantic head on its actually a tractive unit. A tractor unit bears non of the actual load, a tractive unit does.
mick.mh2racing:
If i put my pedantic head on its actually a tractive unit. A tractor unit bears non of the actual load, a tractive unit does.
Or, as BMC used to call them, ‘Prime Mover’s’ which is a term I never heard used anywhere else! 
Pete.
Hi Pete,when I was on a draw bar, the * front * bit was known as the prime mover.
Not sure where the poster is going with this one, is he asking a question or does he have a technical answer to contradict others saying a Tractive Unit pulls a trailer. We know a vehicle moves in a forward direction when a forward gear is engaged and the final drive moves the vehicle in a forward direction, however is the drive pushing the frame forward! If so it could be said anything attached to the fifth wheel is also being pushed. You also have to take spring deflection into account as drive commences, does this deflection result in a push or pull of the frame and all that is attached to it, I’ll let others ponder this problem. In earlier times Tractors were also named Locomotives, the term Prime Movers seemed to be used a lot during the 70’s but the simple ‘Unit’ was the more often heard in my neck of the woods. I once heard a boss from down South call an Artic a ‘Horse and Jockey’ so how many other names have there been over the years? Franky.
A certain bloke from down Leatherhead way is keeping surprisingly quiet about this. No doubt he will come up with a definitive answer before long.
Not that we are obliged to believe him, of course. 
P.S.- He’s still busy with the AEC V8 thread. 
Well I suppose the term ‘Mechanical Horse’ springs to mind even though that was a Scammell term for the three wheeler?
Pete.
windrush:
mick.mh2racing:
If i put my pedantic head on its actually a tractive unit. A tractor unit bears non of the actual load, a tractive unit does.Or, as BMC used to call them, ‘Prime Mover’s’ which is a term I never heard used anywhere else!
Pete.
They are called Prime Movers in Australia.
BRS FH66:
windrush:
mick.mh2racing:
If i put my pedantic head on its actually a tractive unit. A tractor unit bears non of the actual load, a tractive unit does.Or, as BMC used to call them, ‘Prime Mover’s’ which is a term I never heard used anywhere else!
Pete.
They are called Prime Movers in Australia.
Thanks for that, never actually seen it advertised as that in Britain apart from in BMC brochures and workshop manuals. Ford/Bedford/Commer etc didn’t use the term as far as I know in their advertising so I thought that it was just one of BMC/Austin/Morris peculiarities!
Pete.
I’ve also heard them referred to as Motive Units
Being absolutely technical a ‘tractive unit’ forms part of an artic outfit the other being the semi trailer.As such the pin is attached to the trailer and the ‘eye’ is formed by the fifth wheel.In which case the ‘eye’ ‘pushes’ against the pin.The same applies in the case of B train couplings.So the question really should have been does a fifth wheel coupling pull or push a trailer.
Whereas in the case of a drawbar outfit the pin is attached to the ‘prime mover’ and/or trailer and the eye is part of the drawbar.Therefore the pin ‘pulls’ against the drawbar.
As for the Ozzies road trains used to be mainly drawbar outfits obviously using a prime mover and usually semi trailers converted into trailers using converter dollies.After the change to combinations of an artic and drawbar trailers using converter dollies the term prime mover was probably,erroneously,kept on.Probably because a semi trailer that’s designed for use as part of a road train isn’t really just a semi trailer in it’s own right. 
Not a lot of people know that. 
I can see why the question was asked. The pin on the trailer is in front of the drive axle (Except on tag axle trailers) so you could say that the trailer is being pushed.
Carryfast:
Being absolutely technical a ‘tractive unit’ forms part of an artic outfit the other being the semi trailer.As such the pin is attached to the trailer and the ‘eye’ is formed by the fifth wheel.In which case the ‘eye’ ‘pushes’ against the pin.The same applies in the case of B train couplings.So the question really should have been does a fifth wheel coupling pull or push a trailer.Whereas in the case of a drawbar outfit the pin is attached to the ‘prime mover’ and/or trailer and the eye is part of the drawbar.Therefore the pin ‘pulls’ against the drawbar.
As for the Ozzies road trains used to be mainly drawbar outfits obviously using a prime mover and usually semi trailers converted into trailers using converter dollies.After the change to combinations of an artic and drawbar trailers using converter dollies the term prime mover was probably,erroneously,kept on.Probably because a semi trailer that’s designed for use as part of a road train isn’t really just a semi trailer in it’s own right.
Not a lot of people know that.
OK, bag of worms time
Most road trains operating in Australia at the moment are set up as this…
Prime mover at the front that uses a B coupling ie a 5th wheel. Most of the time, but not always the 5th wheel is set on a ball race. The 5th wheel is only there to couple to the pin, the ball race does all the turning, and is locked into position to hitch and unhitch to the pin on the semi trailer. The 5th wheel does all the oscillating. Up until the last ten years or so the second trailer would have been connected to the second trailer via a converter dolly, that would be connected to the rear of the first trailer by an A coupling, VBG Rockinger etc…As would all the other trailer allowing for an overall length of 53.5 meters, usually 1 prime mover, 3 semi trailers, and 2 converter dollies.
Note the difference between an A and B coupling is this.
In the event of a trailer overturning an A coupling ( VBG/ Rockinger etc ) will swivel through the horizontal independently of the rest of the vehicle allowing the trailer to overturn with out effecting the rest of the vehicle.
A B coupling ( commonly known as a 5th wheel ) won’t allow this and will take the rest of the vehicle with it in the event of an over turn. On the whole the Australian government and CSIRO decided that a B coupling was more stable than an A coupling.
New regulations now start that it is possible to us a B-A-B combination as long as the overall length of the vehicle does not exceed 53.5 meters, and it goes like this…
Prime mover at the front coupled to an A trailer, that trailer carries a 5th wheel at the rear which is connected to regular semi trailer and that on it’s own would constitute a regular B Double combination. The rear of the B trailer is connected via an A coupling ( VBG ) to a converter dolly, which tows another B Double trailer set. So in essence it’s 2 B Doubles being towed by one prime mover. There are restrictions on which routes these vehicles can operate on.
Those are the most common Road Trains Used in Australia today.
If your pulling B-A-B’s, sometimes when you get to hill ( especially in the wet ) you might have to drop your rear set, go over the hill and return for it, then try and re couple in the dark. That’s fine if you getting payed by the hour, but most drivers are payed by the K so it ■■■■■.
Some of the trucks that run in the mines on private land are very different, and when you think of mines were not talking about a few k’s from collection to delivery, some of the haul roads are 60 to 100’k from the diggings to the processing plants, and get farther out as the mining work develops.
I hope this clears it up.
OH and just my opinion but prime mover pulls the trailers, if you’ve ever tried to push 3 trailers and 2 dollies backwards you wouldn’t have any doubt at all…
Jeff…
These hot sultry nights have a lot to answer for. 
shirtbox2003:
Answers please.
REALLY 
Most of Leatherhead is lying awake all night.