MIMF

Shouldn't a single/double action truss rod be as effective, regardless if the channel is full of glue?
How would any glue stop the rod from exerting force?
Thanks.

Not sure, but I assume the glue will be very hard, so the trussrod will need to be tightened more, first to overcome the glue, and then the string tension. Fixing it to the neck and filling up the slot will also make the neck a bunch stiffer, and the trussrod needs to be able to move relative to the neck to work.
So, three reasons to make sure to keep out glue out of the slot?

The truss rod needs something to push against (in both directions) so solidified glue could cause it to put pressure on the neck inconsistently.

Rods have threads that may not work well if fouled with glue.

Aren't Gibson and Fender truss rod tight fitting and likewise, unable to move?
Most double action truss rod are encased in a plastic covering and will keep any glue from the gap in the rods.
At some point the rods are no longer moving and solely exerting forced to the underside of the fingerboard.
Yes, we keep the glue from the threads.

The rods in a curved groove you mean? Then still the rod will need to move a tiny amount relative to the neck.

Jarno Verhoeven wrote: ↑Mon Nov 20, 2023 6:47 am The rods in a curved groove you mean? Then still the rod will need to move a tiny amount relative to the neck.

Exactly. The rods will move a bit and if you have glue in there the rod will break free of the glue as it moves. It is not comforting to hear loud cracking sounds when you adjust the truss rod. No one puts glue in the truss rod slot so why do you think it is appropriate?