Morning all
Something happened last night that I’ve never had before and wanted to put it out there for the masses to hopefully answer
The firm I work for mostly has decent kit but last night had an older trailer, when I connected I did the usual checks, reversed in so far, got out, checked the fifth wheel height and raised it so the fifth wheel was high enough to see no daylight between it and the base of the trailer, reversed in, pull check happy days, finished connecting and my checks then went on my way,
However, when I was starting from a stationary position, the unit moved followed by what I can only describe as a knocking feeling, as if the unit moved forward then a split second later the trailer followed, now during my pre use checks, I was advised to get in between the unit and trailer with a torch and check the lock was properly across the pin which it was, last night after getting this knock I stopped, re checked but everything seemed right, the trailer was seated correctly on the fifth wheel, the dog clip was in, the lock was across the pin and the lever to release the pin was seated correctly,
Has anyone else had this?
Thanks all, mick
Usually u will get a bit of play with age
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That’s what I hoped to hear, after doing the checks, then checking again I couldn’t see what if anything id done wrong, was on my mind all night driving back up
You will find sometimes you will get the same feeling with heavy loaded trailers.
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It was a heavy load to be fair, full front to back, maybe that’s what it was, older trailer fully laden, either way it was a new one on me, another lesson learned though
It’s as said it’s worn . Old pin gets worn then you get slop .
If you get a really worn pin & a unit with slack jaws - it can be a really uncomfortable ride - specially in stop / start traffic: as you say a thud as you pull away. Then another when you stop and the trailer stops momentarily after the unit- then you pull away again etc …etc 
To be honest I was confident I’d connected up properly, double checked and still had the thud, not a good drive back but at least I’ve a better idea now, hopefully get a decent trailer when I’m back in Monday night
I hear some awful loud bangs coming from skellies with containers on. Even at low speed they often seem to make sudden bangs when manoeuvring them around the yard. That isn’t your issue in this instance, but I think the point is that with all that metal, weight and kinetic energy there are bound to be some consequences.
Stick a defect in for worn King Pin, unless it happens with other trailers you tow meaning its worn fifth wheel.
If i have a combo with excess slop and i happen to be near the workshops i usually get one of the mechanics to have a poke nose whilst i juggle it back and forward, did this couple of weeks ago so they booked my tractor in to have the fifth wheel mechanism looked at.