Anyone know what causes trailers to dog tail?

Usually it's because the tandems are misaligned due to someone jackknifing while backing with a heavy load

 

Sharp u turns can cause alignment issues especially guys that do this in tight lots like trk/stps at a high rate of speed.
Curbing tires also.
Heck we've had brand new trlrs come from the factory and weren't aligned correctly from the start.
If your fifth wheel isn't greased good enough it will sometimes simulate a misalignment.
A dry fifth wheel will also cause you to saw your steering wheel.

 

I'm confused I assume you mean rock back and forth why would a dry fifth do that?

 

Too much weight at the back of the trailer can cause a pendulum effect.

 

If its a significant Off-track, trailer was probably in some sort of crash and the tandems are no longer aligned with trailer frame. Or possibly something has broken in the axle-suspension-frame assembly and an axle has shifted back or forward on one side.

 

A dry 5th wheel can usually be "felt" with subtle "shifts and pops" on smooth roads as the "friction hold" at the 5th wheel gives way.

 

Axles are out of alignment for whatever reaaon.

You see 4 wheelers doing the same thing once in a blue moon. More common on older rear wheel drives and pickups.

 

Most storage trailer I've pulled did that, and those trailer looked like they were abused.
Look in the mirror and you could see one side of the trailer, and the other mirror could only see the front corner. lol