from what I can make out moving the aperture ring moves cam A (Red)
which moves part B (yellow) backwards and forwards
that movement Should be transfered to the aperture by lever C (Blue)
at the bottom of lever C (tricky shot!) some how is suposed to move the brass bit to open and close the aperture
neither the top end of lever C is getting moved by rotating the aperture ring, nor if I move it manually is the other end connected to the brass aperture actuator
Any ideas? It'd be a shame to loose this one.
Rotating the aperture ring indeed rotates the cam ring A which then moves the aperture mechanism B back and forth. The aperture actuator mechanism C is a totally separate mechanism from A and B. The tiny brass bit at the bottom of C is just the visible portion of a larger rotating part which isn't in direct contact with the lever C.
The aperture mechanisms within these older Tamron lenses are not subject to failure due to broken or loose parts. Instead it appears that internal dust building up on a fine oil film on some of the aperture assembly's parts has gummed up the aperture to make it stick from time to time. Further disassembly of the rear of the lens is required, yet it isn't very difficult on this model once you know what to do.
I am really busy at work and some CLAs, but will post some photos and instructions for you in a day or two. You will have the aperture working and the interior of the lens nice and clean in no time! Just be patient for a day or so.
for information about vintage Tamron manual focus lenses.