1996 Toyota Celica speedo stops working

hello, i drive a 96 jap import celica. when i bring the car up to 140kph the speedo stops working.i would have to spot the car for approx 20mins for it to work again. this also happens when i go on a long trip. after driver for over 2 hours if i stop a lights a move off again the speedo wont work. any ideas?

thanks