Yeah i haven't driven faster then 85 yet with my car and i know it sounds like a stupid question but what would the dual needle do after 85 does it keep going around like a clock or does it stop?

 

It would probably hit the trip odometer reset button or the small metal pin(if it has one) just before the reset.Any faster would more than likely not hurt it.The speedo needle is NOT mechanically connected to the speedo cable.The cable drives a wheel(may be magnetic)that goes into a small metal drum.These two do not touch one another.This drum has a pin that goes out toward the speedo which the needle attaches to.When the cable spins the wheel spins.This cause the drum to rotate(via magnetism??)which in turn makes the needle re-act.You can theoretically break the speedo, but i think you would have to go way beyond the 85mph mark to to this.

 

It pegs the the trip thing. Ask me how I know. At least I couldn't tell a cop how fast I was going. If he were to ask.

I swapped my 145mph(to save the low miles of 452.5 on it) one out of my 87 L98 IROC and put a spare dual needle one in it's place. Adam :-)