Chevrolet Repair: Spedometer problem, vehicle speed sensor, chevy caprice

Question
1991 Chevy caprice wagon 305v8 AT. Sometimes the spedometer doesnt start working for several miles, particulary when cold. It is not a digital dash, just a standard sweep needle. Any hints?
Someone told me there my not be a cable but some type of sending unit.  

Answer
Hello William,
The pickup is a vehicle speed sensor, in the side of the transmission. Sends pulses taken from a magnetic pole piece on the tail shaft.
Make sure the connections are good.
That speed sensor is quite cheap, and can be bought at AutoZone.

Of course it could be something in the dash also. Does the odometer work when the speedometer doesn't? If it does, the VSS is good, as well as the connection, and looking at the speedometer itself may be what is needed.

Van