Join Date: Jan 2002
Location: Melbourne, Australia
NOTE: The following relates to Series 1 33 1.5 Twin-Carb model cars (may be different to your 1.7):
I have seen many a 33 with speedo problems...
My first Series 1 33 speedo didn't work at all and it was recommended to me to bypass the plug on the back on the instrument panel, and just connect the electric speedo wire from the gearbox directly to the contacts on the rear of the speedo itself. Aparently the loom/plug device can be quite faulty. I have since noticed this modification on a few 33's (quite common).
My 2nd Series 1 33 speedo also didn't work. It had already had the above mod applied, so I was unsure of what the problem could be. After much tinkering all I did was put a small screw into a little screw-hole on the rear of the speedo/instrument panel. This screw-hole was just sitting there by itself, and looked as though it should have something in it. It had golden circuty/contact type thing around it, and I thought maybe without a screw in the hole, something wasn't earthing correctly. Seems to have fixed the speedo, which is great!
Other than that, all I can recommend is removing the speedo sensor from the g'box (from memory it is only held in with a C-clip - though it can be a pain in the ass to get your hands in there to get it off), give it a good clean, check the condition of the wires coming out of it, and follow it all the way to the instrument panel checking the condition of all the plugs/wires involved.
I don't think it is possible to open the speedo sensor, mine seemed very sealed and unopenable.
I apologise for the poor level of terminology used, I'm not the best when it comes to electrical stuff, but give these things a go, and let us know what happens...