That is, typically, a cable that is biding, not the display.

You would try to lubricate the cable from the engine compartment back. I use a synthetic lubricant (Mother’s Milk is suitable) and I apply it by removing the cable at the engine, putting a clear plastic tube over the cable, using tie tapes to crimp the plastic down as tight as I can make it, then I pour the lubricant down the plastic tube so that it goes inside your sleeve of the tach cable. The dryness that causes the cable to bind (which is what your problem sounds like) is caused by heat from the engine compartment. You do NOT use a petroleum based lubricant, like oil etc. It should be a synthetic lubricant and work it into the tube and, in turn, into the cable assembly, as best that you can. To assist the function, you could even have your mechanic open up the panel, remove the cable from the back of the tachometer, and work it back and forth so it assists the lubricant to get farther into the cable assembly. As you do this, you will see black gunk coming out of the assembly into the clear tube as you pour the lubricant into the tube, and this shows that the old goo is coming ut and the new lube is going in.’
This should last you some years – perhaps five, before you need to do this again. The same procedure applies to all of the cables – they must all be lubricated when they start to bind.

Pat Barry