got to a drop and as i reversed on to bay i could here a light tapping noise , gets out looks all under trailer truck but couldnt see anything amiss so put it down to one of those things.
loads up pulls of bay and listens for noise, no noise so drives 100 miles back to yard , all fine untill i try to reverse on bay , i can reverse but noise back but alot louder.i then report it so shunter and few others come out to have a listen/look , no noise going foward but you can clearly now hear banging noise when going back.
using torches etc they think the noise is comming from 5th wheel area but as dog clips in and jaws are closed cant see it is that, so drop trailer and pull out[ took a bit to get jaws to disengage]. we then try and lok at 5th wheel but nothing obvious so they think it could be truck , good check again , nothing obvious , check pin on trailer, again nothing.
so i suggested running truck on own then reversing it to see if noise still there , truck fine , reverses fine so has to be something to do with 5th wheel , so no ifs or buts sent straight to scania as to risky to send out even though no obvious fault other than banging noise when reversing with trailer on.
when i get back in yard tonight shunter says they had to replace jaws on 5 th wheel [ not sure exactly wrong with them just they had to be replaced].
now as it was a 60k truck , nearly new , trailer only a few weeks old , how would they wear out that quick, assuming thats why they were replaced , im assuming there was play between pin and jaws.
or my other question is assuming it was a deffective casting of either jaw[ or something like that, how would you stand if they failed altoghther, trailer came off, youd checked dog clip was engaged , jaws locked [ paranoid so always have a look underneath with torch] before leaving yard, had a look when you 1st heard noise, but not sure where noise came from as no obvious fault so you carried on. would it be your fault.
lastly , has anyone ever lost a trailer through deffective jaws, 5 th wheel , even though dog clip etc were in place ta
happened to me 2 weeks ago and i was suspended until and inquiry. 
i hooked up the trailer an empty skelly everything done correctly got a mile and half up the road and the trailer fell off. 
the jaws were still closed but we dont have a dog clip we have a handle … anyway everything was in place. they blamed me to start with until lucy pointed me in this direction…
and
if you use the search button and type jost there are a few threads on there.
anyway i printed of a few threads and looked up on the internet and printed a bit of there. i had the inquiry armed with my info stuck it too em that the 5th wheel was faulty as i know i know that the trailer was fine and connected properly before i left. 
.
i got sent home then called to come back to work the next day to carry on working, when i got back to work i found out that they had a 5th wheel specailst into check the 5th over and he replaced everything apart from the actual 5th wheel plate, he replaced all the jaws and locking mechanisms.
so sometimes they can become faulty, now i check like lucy with my torch to make sure the jaws is inplace.
ady1:
has anyone ever lost a trailer through deffective jaws, 5 th wheel , even though dog clip etc were in place ta
Yep. Driving a Scania for NFT, i went from Crick to Sainsburys at Harlow, unloaded and when i left Sainsburys the trailer came off and overtook me ! 
Everything was closed up , hooked up and clipped up properly. Even though i was pulling a fridge the only damage luckily was the airlines which an onsite fitter repaired and the tug came (from Sainsburys) and lifted the trailer up for me. NFT insisted i still do my collection before returning with it. When it came off it overtook me and veered off down a small side road, it would of killed someone if they where coming out of it 
Years ago we had a trailer come off just outside a high street, everything was as it should be apart from the Jaws missing now the police vosa the fitter and the boss were walking the mile back to the depot scowering the road for any metal objects that could be any part of the 5th wheel nothing found driver was cleared of all blame. By the way he was ■■■■ lucky as the trailer came off and stopped just short of a car with mum and 2 kids on board