Intermittent speedometer

could use some advice on why my speedo would go dead occasonally. Seems to happen about 2-4 minutes after starting in the morning and lasts about 2-4 minutes. my timing observation could, in-fact, be a pure coincedance however.
87 911

Probably a loose electrical connection, either at the back of the speedo, in the tunnel between the back seats (there's a connector under the metal panel) or at the sender at the transmission.

This problem is a sticking speedo head or the sender on the trans. Make sure you replace the hold down clip on the sender!

Good Luck,
Lee