Speedo goes to 0mph randomly for a few seconds.

[Birdie*]

Before anyone says I've stopped the car I'm not lol. But it's happened twice now when on dual carridgeway the speedo will fall 0, then a few seconds later bounce straight back up to 70 without anything feeling different in the car. It's done it once joining the carridgeway but this time I was just behind a lorry and saw it fall then instantly go back up? All the other dials are perfectly fine though.

Any ideas on what this could be?

 

[*Wilson*]

it will be your speed sensor on the gear box. give it a clean if that don't work get a new one from the stealers.