98 Mazda B3000

My 98 mazda b3000 w/ 18x, xxxmiles, stick shift, 2wd, had the speedometer stop working. I changed the rear end from a factory rear to an open rear w/ 411's six months ago. Recently the clutch started going bad. The speedometer failed before any issues w/ the trans, and after the rear end replacement. I've been told there is a vehicle speed sensor in the rear, but no parts store recognizes it in their system. My tach still works, and my abs light is on. Why dont I have a speedometer?