I would take the cable nut off the speedometer and pull the cable out of the jacket. The cable kits we get today all come with a nylon or plastic square drive, they are installed by heating the cable and pushing the heated cable into the drive. If someone like me at my age with a bit of the shakes tries this you end up with a poor attachment which will slip. I prefer the crimp type ends if you can find them. Next dry cables cause jumping as someone already stated clean up the cable and lightly lube it with 101 Lubriplate which I think is the best for the job. This condition does not cause speed errors just jumping of the needle. Finally sometimes the driven gear at the transmission (plastic) will round out where the square end of the cable enters and slip replacement with like number of teeth gear is the fix. As far as the transmission main shaft gears they used to be steel (actually part of the shaft) so those last forever, I do know they have been replaced with gears driven by a round ball bearing as is cheaper to mould a gear rather then machine it. I believe that started in the C4 days, you'll have to check everything else first. Hope this may give some sort of help. kotzy

 

too bad my gear in the tranny is not metal. i have to replace the nylon gear now. i have the 4 spd. 6.9