09KZMXT266 wrote:
---Did the Andersen hitch plate somehow do it? Totally confused, and looking for your thoughts....
There's been much speculation about the cause of the damage -- so I'll add mine.
IMO, it is most likely that the Andersen plate is the cause of the damage.
We must keep in mind that the plate can move relative to the TT's tongue on all three rotational axes -- pitch, roll, and sway.
A key explanation was provided by Bryan (
carringb) --
"
They only rotate as one and even then, the urethane springs will allow a small amount of independent rotation until the springs provide enough force for the ball to breakaway and rotate within its friction cup.
The plate will also move fore-and-aft relative to the trailer frame as the vertical angle changes between the truck and trailer, such as when entering driveways with dips or going over speed bumps.
"
The OP's first photo clearly shows the top of the plate was rubbing against the underside of the broken weld bead.
The elongated shape of the worn area is proof that the plate can rotate in yaw just as Bryan explained in his first sentence above.
When the TV turns to the left, the plate will rotate counter-clockwise (viewed from above) relative to the tongue until the static friction between cone and ball spindle is overcome by changing chain forces due to compression and extension of the polyurethane bushings.
Another important thing happens when the TV turns --say, to the left. The relative yaw angle between TV and TT, causes the WD pitch-axis torque applied to the hitch head to exert a roll component of torque which causes the TV to roll to the right (CW when looking at the TV from the rear).
When the TV rolls to the right relative to the TT, the left side of the plate rises up relative to the left side of the front of the tongue.
Keep in mind, the OP stated, "
My frame is 8". There may be 1/8" of clearance is all.
It wouldn't take much relative roll to close that 1/8" (or less) gap between plate and tongue.
So, we're in a left turn. The WD torque is attempting to roll the TV to the right, and the left side of the plate now is in contact with the bottom of the left weld bead trying to resist further rolling of the TV.
This provides the opportunity for the plate to exert a very large upward force against the bottom of the weld bead.
The friction torque between the Andersen's cone and spindle causes the rear of the plate to try to move to the right as the TV turns to the left.
Since the plate is being forced upward against the bottom end of the weld bead, there will be a friction force to the right in addition to the upward force on the weld bead.
The right-directed force on the bottom of the bead would tend to "unzip" the bead from the metal to which it was (perhaps poorly) attached.
The upward force on the bead would cause the buckling and cracking of the metal at the top of the bead, because the bead is much stiffer than metal above the bead.
I can see several reasons to believe the damage was caused by the hitch.
I see no reason to believe the damage was cause by a fork lift.
Just my thoughts --
Ron