afterall how do you know you are not breaking the speed limits?
Exceeding the speed limit is still illegal even in places where the lack of speedometer is not illegal --- they just don't care how you know your speed.
Exactly. I drove my Alfa Spider for over a decade with an unreliable speedo. I learned the multiplier for third and fifth gear from tach to speed, got a friendly town cop to verify it with his radar gun, and drove that car over 100K miles without ever being stopped for speeding.