when you refitted the front end, the locator for the speedo cable needs to be at a certain angle, if not you stretch and break the cable internally, a mistake often made by tyre fitters not familiar with dukes at it has a habit of rotating when the wheel is removed / fitted.

Just follow the cable down and turn the handle bars both ways, you wil see immediately any tightness ...

New speedo cables are abou £12 I think .... easy fix so dont worry ....