Always visually check this!!!

When you park, set the trailer brakes then move the tractor forward a bit. The pressure on the jaws means they can't be released.

 

If I think I'm in a sketchy area, I'll set trailer and put forward pressure on pin before setting tractor.

 

I do the same.

 

Just this past week I saw two dropped trailers in intersections. So those drivers were able to drive some distance before it slid out underneath. My guess is the king pen wasn’t locked in the weight of the trailer on the fifth wheel was enough to pull it along for a ways anyhow.

 

I have had the jaws release, the 5 th wheel plate was bent. Took it off , put a little heat and a big hammer, good as new.

 

Is the tug test really not enough? I never got out and looked at the jaws. I was with a guy who had been driving for years and he didn’t know about the tug test when we hooked up to a trailer. I had to show him how to do it

 

No it's not. I've twice now tug tested, but when I looked the kingpin wasn't seated in. Next time look at the kingpin. Notice that there is a recessed area? If the jaws catch the thicker part under that collar it will pass the tug test but will pop out after a couple of turns or rough road.

 

Agree on pressure against the fifth wheel.
Yet... can’t set trailer brakes in winter cold. So back to checking.
Ive even had an idiot bend my license plate up while I was inside. Punks will do anything to destroy.

 

While it typically doesn't happen at Truckstops, sometimes when you have an uncoupling it's not always caused by someone pulling the pin! Sometimes it's caused by incorrectly backing under a trailer! Also sometimes the 5th wheel is broken! If that kingpin is not sitting in that 5th wheel correctly and then the rig is turned sharply the locking jaw can get into a bind and it can release the kingpin. Has already been said, GOAL after backing under and make sure you did it correctly. Some of you new drivers might not have seen this happen! I have several times and it almost happened to me at the Hershey warehouse near St Louis. I got complacent then in a hurry I failed to pay close enough attention to my coupling. I had to make a sharp almost 180 turn and thankfully was watching when my trailer made a lateral move and I knew it was loose. I was able to stop and lower the landing gear and the yard man helped me get it up and this time I did it right. Another problem is drivers that hit those kingpins with so much force they push the trailer back 10 feet when backing under! Easy does it! There are tons of videos on this subject! As to what the OP is reporting you never know when moron will happen!