Get a pair of bent nose needle nose pliers. They are small and usually come in a set with wire cutters, etc. I think Sears may have them. The bent nose allows you to get your hand above the needle and makes pulling easier. Don't squeeze the pliers too tightly or you will be pulling against the shaft and not the needle.

As Steve mentioned be sure to bend the need up enough to allow it to settle to its zero MPH setting. Mark that place so that you can put the needle back 'in time'.

When you get the speedo out disconnect the rear part where the cable comes in. Inside is the magnetic coupling that connects the cable to the gear system. Check the screws inside there for tightness. Most have a dot of paint on them to keep them from backing out-or so they claim- but they do back out. I had this problem in my 1977 450slc. Cost me a $200 speeding ticket in Virgina.