Tapping the clear plastic over the speedometer has been necessary at times, and has worked since I bought this 94 Cherokee 11 months ago and, at some times in recent months, the speedometer has worked without tapping, possibly when the Jeep was driven more frequently.
The odometer and all other gauges work OK, but tapping the clear plastic, with more force, seems necessary every trip now to see speed displayed.
Even stopping at a stop sign now results in zero needle movement for a few seconds, followed by the needle jumping from zero to apparent speed.
Could the needle's bearing just be flawed, or is a problem with the wiring or vehicle speed sensor more likely? Thanks for your advice.

 

I would like a little info on this as well. Mine is not quite so frequent but there is a definite similar property about it.

 

Spraying silicone directly onto the needle bearing may have helped.
Removing the black dashboard trim(1 'treaded' plastic plug and 2 philips screws, above the instrument panel) and the clear plastic(4 brass screws) was necessary. Removing the instrument cluster would/will be next, if necessary, and would help cleaning out some obvious dirt, but cluster removal has been conservatively 'saved' for later. With the clear plastic removed, only subtle tapping was needed to see the needle display speed, and I sprayed the silicone at ~20 km/hour. Earlier, I'd removed the plug from the vehicle speed sensor, and replugged it without removing the sensor from the transfer case.
But it's tough to see how the sensor could be involved, when tapping close to the needle makes it work.