5th wheel issues. Didnt know where else to put this.

I can not say this is what happened in your situation, but years ago my husband and I had a truck that had an automatic fifth wheel release, we had hooked up to a trailer and pulled it over a 1000 miles, pulled into a truck stop hit a bump and the trailer fell off. We were lucky it was a light load and landed on the landing gear, some drivers helped dolly it and a driver used his truck to move the trailer, we went to a Volvo dealer, they had to disconnect the auto fifth wheel release, it was stuck half open and half closed. They said more then likely what happen was it closed when we hooked up, but it was not working correctly and the air was pushing the jaws open and when we hit the bump it was enough for the trailer to pop off. I thank god it happened in the truck stop and not out on the highway.
If you have one of those maybe something similar to that might have happened, very scary!!!

 

This is why the "tug test" is not always accurate...
You should always crawl under the trailer and make sure that it's secure..
Is it a pain in the arse to do it.? Somedays it is..
Thankfully your mishap happened at low speed and nobody was hurt.

 

Also check before you leave after a night at rest stops or truck stops.....

 

Your tires caught some road debris, which mangled the puller and opened the jaws. The trailer slid back and/or popped up causing the king pin to end up on top of the jaws (and reclosing them). The pin rested on top and you were darn lucky to have gotten it into the dock with out dropping the load. The trl slid out when you pulled away from the dock because the drag from the load was heavier than when the trl was empty.

My best guess.

Ken

 

My guess, which is only that, is that you hooked up but the jaws did not lock around the kingpin, like someone else said you had enough weight on there loaded to keep the trailer on, which Ive seen happen. On the bent handle, was it bent forward towards the truck

 

From what it sounds like, you checked the mushroom bolt and did a visual to make sure the locking bar was across, which it sounds like it was.

However, you didn't mention a visual inspection of the king pin itself. Not only does it have to be seated in the crotch of the fifth wheel, it also has to be fully visable underneath the locking bar. If you look at the pin...its basically one solid cylindrical section of metal, with a narrow spot. That narrow spot is where the locking bar should slide across. You should be able to see the wider part of that pin underneath the locking bar.

As far as the release arm...it might be damaged because the trailer wasn't properly connected. It sounds like the pin was on top of that locking bar, which I dont think is designed to take a vertical load ontop of it and as you were driving down the road...that pin kept bouncing down onto that bar.