In the case of Miata/MX-5 NA model to all the differential final gears there is a matching driven gear unit for the speedometer's adjustment.
In the case of Miata/Mx-5 NA models the gear for the speedometer is rotated while being linked to the main axis of the transmission.
This gear is called the speed driven gear.
The output of this driven gear is being transmitted to the back of the speedometer by the wire’s rotation and the speedometer is being operated in this way.
In other words it is mechanical.
Picture of the driven gear setup
The wire is extended.
In other words, starting with the NB models, the driven gear becomes pulse unit and there is no more need for the wire.
We apply voltage to the unit, develop a pulse and move the meter by the pulse count.
The NB models’ unit is monolithic, cannot be dismantled and only the driven gear cannot be removed.
The NB pulse unit cannot be dismantled.
We can see the coupler used for the pulse.
In NA models the unit can be dismantled, therefore the driven gear itself can be removed.
This means that the gear as separate item can be exchanged.
Maruha’s original driven gear (for final over 4.6 and 3.99) with the genuine 4.1 and 4.3 ones offers a product lineup that can be a compensation for all types of final gears.
This time we’d like to introduce the unit setup with all types of driven gears.
The driven gear is being prevented from falling out by a pin of 2mm diameter (formal name: spring pin). For the gear exchange a 2mm pin punch is necessary.
However one doesn’t own such a superfine punch, unless one is a professional.
We, at Maruha provide it with each unit.
If the car is jacked up horizontally, mission oil can leak out when removing the unit, so we have to be careful.
It is possible to avoid leaking if we jack up only the differential side.
In the case of NA6 a plastic collar comes in between the unit and the wire (guide seal gasket).
You cannot find it in the case of NA8.
In the case of Maruha’s unit there’s no collar neither for NA6 nor for NA8, you can reuse your actual one.
All those customers who can manage the dismantling and setup by themselves, can get the driven gear as a single item.