Lost the Speedometer WTF?

[DAKSY]

Riding to work this AM, yeah, I know it was 29 degrees...
BELIEVE me, I know!
Anyhow, cruisin I-90 at 68 - 70 & I look down at the speedo & I watch the needle drop to nuthin!
Stays there for about a 1/4 mile, & then climbs back to speed...
Didn't act up for the rest of the ride or the rest of the day for that matter...
Any ideas as to what/where I should investigate?
TIA...

[JerseyT]

Speed sensor may be coated or on its way out. Over time the magnetic pickup gets coated with metallic swarf from the transmission case and the speedo starts to act erratic. Try pulling the pickup and wiping it clean. Simple things first.

[DAKSY]

Will do. THX