mk2's had real issues with the pot metal gear letting the shaft slide out.. mk1s tend to break that gear but my 81 coupe has the broken plastic and bad pot metal piece.. aka why i posted the one link for diy.. what you putting a tach into a mk1??? i got some really nice pics of how i made up a mk1 diesel cluster with factory mk2 tach and vdo BOOST gauge... requires the 81 and older dasher/jetta cluster though... shift light kills it on 82+