speedometer

on my 1975 h2, my speedometer really acts crazy.the needle jumps all over the place .when it gets steady i can in 5th gear and the tach shows 3000 rpm ant the speedometer will show im doing 70 mph and i know im not going that fast. has anyone ever had that problem?   tia...hydro

A few common issues with these. I would pull the whole assembly off to check this stuff, they of course come off as an assembly. Check with a drill in reverse using a square drive per each gauge. These are prone to gauge cable input thread detaching, see it all the time. You will note this upon removal of female barrel of cables. Next thing is the weeping of damper fluid from cup down into rotating drive bell and needle mechanism stop. The fluid, contrary to a lot of AI Slop, isn't oil at all. Its a silicone based "tacky, not slippery" fluid. This, while great for dragging the needle around, isn't great when it spills onto the mechanical magnet and drag cup assy. Being a 1975 H2, you should have speedo faceplate with 10th increments and tach with a 7500rpm redline, not like one shown but internals are identical. Try the thread checking and drill technique first, everything else the gauge has to come apart.