The knob under the dashboard will adjust the headlights on my Red Special, but at present it offers the option of a range between "dipped quite a lot" and "quite dipped".

Apart from bending the brackets the headlight shells sit on (or more likely bending the shells), is there some further scope for adjustment?

The threaded adjustment mechanism on the light bar at the end of the long rod from the dashboard looks a bit battered, and I am loath to try bending that in case I snap it off.

On my 1964 H-Van, which uses what are said to be 2CV headlights, the metal headlight shell sits on a thick cup-shaped washer. If you loosen the 19mm nut underneath, you can re-position the headlights quite a lot: the hole in the mounting bracket is oversized. Of course the H-Van doesn't have any other way of adjusting the headlights: the mounting brackets are welded to the panels on either side of the radiator.

And I wonder whether the older 2CVs used a similar cup-shaped washer?

P1000993 by Robndaisy, on Flickr

The set up on the AZU.

P1010185 by Robndaisy, on Flickr

The set up on the Charleston.

P1010187 by Robndaisy, on Flickr

Once slackened, plenty of adjustment .

Thanks Rob. I'll start squirting in the penetrating oil.

If both beams are at the same level and the headlamp mounting/adjustment nuts are seized, you can raise the range of the internal adjuster mechanism by adding another washer under the split-pin (or R-clip). This will swivel the headlamp bar to a slightly higher angle, raising both beams.