Burns Gearbox/Truss Rod Adjuster
Perhaps someone can lead me to a source, or can draw/explain the Burns truss rod, installed on my 1976 7660 Gretsch. I'd like to know how they mechanically work and appear in the neck. The reason I ask this is because, my Nashville model has one of these truss rods and I can't seem to get it to change the relief in the neck. The guitar, by the way, is all original and has had very little use—a real find!
However, perhaps I am not checking the relief correctly. I have been capoing the 1st fret and holding down the low E string at the highest fret—then checking clearance around the 7th fret. I'm lucky if I get .003" clearance. I can't say the guitar frets out in the middle of the neck, but there is some slight buzzing around the first and second fret, which probably could be eliminated by raising the bridge. I would like to set the neck correctly, regardless.
My concern is that I have turned the truss rod key many, many turns CCW with no change. It seems the number of turns is limitless. I can't believe the truss rod is dislodged, because this guitar is in near-new condition and I'm sure I'm the first one to ever remove the adjustment plate on the back of the guitar (I happened to get the guitar with all the original tags, truss key still sealed in the factory envelope, etc.). There is even, moderate drag when I turn the adjustment key, so nothing seems "broken" about it.
So, by seeing the actual mechanism, I might be able to determine if the truss rod is actually damaged/dislodged, or perhaps the key post is disengaged. My other thought is, perhaps this truss rod works on an eccentric mechanism (cam-like), so all adjustments can be done in 360° of key rotation. Maybe my constant turning of the key is simply going through the tightening/loosening cycle each revolution.
I have light strings on it (.010-.046) and intend to put .011-.052s on it today, thinking that the increased tension might increase the relief.
I have searched all over the internet for some answers, but don't seem to find anything of use. A photo, drawing or a detailed explanation would be greatly appreciated.