May I undersling the TB3? – Sure can BUT – there is a single point of failure that could result in disastrous consequences for your camera it were to happen. Did I get your attention? Nobody has had any underslung issues and I want to be sure we don’t.
A set screw in on the large round gear on the inside of the box can come loose over time. What can cause this loose set screw is repeated pressure or force against the pan drivetrain – this could develop if you travel with the TB3 in a suitcase where the head isn’t protected, or have dropped it.
Check the set screw tightness before you start. You can do this by a couple different ways:
1) First is the direct way by opening up the box and checking the stainless set screw is tight against the pan shaft. Again this is the set screw that goes through the large white pan gear on the inside of the box. In the little toolbag we included is a wrench that will fit this.
2) Indirect way is to grab the head with your camera off and wiggle it try to pan it back and forth with light to medium force – don’t go gorilla on this, but be firm. Wiggle this several cycles. What you are looking for is rotation without any pushback from the geartrain. This would indicate excessive and increasing backlash in the pan axis – That set screw is loose and need to be tightened.
If all is tight, you are almost good to go, but check it in one last way. Try to pull the head straight off with twice as much weight as your camera setup. If you can’t you can be sure it’s not coming off during your run.