Fifth wheel jaws locking on their own?

How old is the 5th wheel? If it's doing that, I wouldn't trust it to stay locked with a trailer on it. I've never seen one do that before.

 

I would have the 5th wheel assembly inspected by a mechanic and properly adjusted. Then, if it happens again I would replace the top plate of the 5th wheel with a new one. I have purchased some good used ones in the past but in a situation like this I would only buy a new one.

For an example, I recently purchased a new top plate from Fleet Pride for $799.99

 

Depending on the brand it may be possible for a high pin to close the jaw.

How far did you bobtail?

How smoothe were the roads?

Mechanical things wear out it might be worn enough that a good bit of rough bobtail might bounce it closed.

Looks like a re-build/replacement should be done now.

 

Out of adjustment most likely. Had one that would do that when I was a newbie the shop fixed it. Didn't bother to pay attention to how because new guy.

 

How far are you bobtailing? I’ve had mine be closed after bobtailing about 90 miles round trip to the shop on fairly rough roads.

 

Mine does that sometimes, after running over rough ground.

Sometimes happens when I'm about to pull out from under a trailer, drop the air, and it will pop shut enough to snag the kingpin. My cure is a bungie from the handle hooked on the fender to keep it released until I get out from under.

 

I'm driving a 2021 and that's a usual accourance for me, I bobtail home often so I know before hooking I need to pull it open

 

I hate those fifth wheels with jaws.
I have one with a triangle shaped bar that goes across to lock the kingpin in. They are for heavier hauling in general. A better fifth wheel.

 

1972 Chem Leaman got new Macks, first time using Imron paint. ASF 5th wheels, jaw drops down. One driver took a load of cement around 100 miles, unloads part and backs up to reach the other silo. hit the brakes and the trailer slid off...all kinds of nerdy guys with pocket protectors and a guy in coveralls with a big bar spend the afternoon out in the yard with that unit. They were from Mack and blamed the paint...