My B3's speedo used to have similar problem. Speedometer didn't worked at all, only sometimes it did some motion
First, I disasembled it for some ten or twenty times, without any effect. Then I got idea that speedometer sender may be deffective - I borrowed it from junkyard - nothing. Then I borrowed instrument cluster from neighbour's american B3 - it worked, so problem was in my instrument cluster. There wasnt anything wrong on PCB, so I tried dissasemble speedo clock, in process I damaged it
So, at last, yesterday I bought instrument cluster from B3 coupe 2.3 and used it as a donor [some time ago I did similar thing, only for other reasons
], so now I have working 260 kmph speedometer instead of dead 220 kmph one
