Odd speedo behaviour

[MKnight702]

Does anyone else have a speedo that won't register low speeds, and how (if at all) did you fix it?

My speedo won't register below 30mph, the needle stays on 0 until I hit 40 then works properly until I drop below 30 when it drops to 0 and repeat.

Do I need to clean the connectors, adjust the gap or replace the sender? Or do they all do that?

[F.C.]

Adjust gap first.