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Howdy,

Discussed this with a few people but hoping to get more feedback on resolving a problem. I've got a 4.78 final drive in a car. I want the speedo to read the correctly. There don't seem to be any solutions to suit the 4.78 though the closest is Maruha (4.6). I'm guessing I'll have to go down the custom route for the speedo gear?

~ Garidoooooooooooooooooooooooooo

NA mechanical or NB electric sender?

For an NA not much you can do.

For an NB you can buy and use a Speedo corrector, essentially they just wire inline with the sender and adjust the signal sent to the gauges.
You'll need to use a gps Speedo on your phone or something to set the correction factor correctly, but once that's done it should be fine.

Also, you may not even need to change the sender gear if the overall change is within the % the adjuster can do.

hks_kansei wrote:NA mechanical or NB electric sender?

For an NA not much you can do.

For an NB you can buy and use a Speedo corrector, essentially they just wire inline with the sender and adjust the signal sent to the gauges.
You'll need to use a gps Speedo on your phone or something to set the correction factor correctly, but once that's done it should be fine.

Also, you may not even need to change the sender gear if the overall change is within the % the adjuster can do.

D'oh, i knew i left out one detail. The car is an NA6 so NA. Surely one can be custom made somehow?

Hmm, while I'm sure it's possible, you'd need to find someone who can sit down and do the maths to work out the correct number and angle of the teeth to properly mesh with the drive gear.

Then find someone to manufacture the part (at least with the prevalence of 3d printers this is far easier now)


Maybe also look into Speedo gears from cars like the RX7, 929, and B series utes.
They all used gearboxes the same as, or very similar to, the mx5 5 speed.

You could also include earlier Mazda rwd cars in that list, as well as the E series vans.

Not sure if the gears are the same, or if any of them had a similar diff ratio to your need, but it's at least another potential avenue.

Another avenue.

Check out what kind of drive a Kia sportage uses.

They were a 4.78 final drive (prob what your diff came from)
IF the Speedo gear is the same type as the mx, it should be spot on.



Edit: 4.78 was the USA Kia ratio, can't guarantee Aussie ones were the same.

if the gear is a plastic moulding with teeth then I reckon making it would not be an easy thing- same for printing - someone still has to do calcs and then print and its time and money. I bet there is a plug in unit like a Satnav that gives the speed. Guys running old cars with MPH manage to get around it even with stick ons taped to the dash or speedo lenses.

Mr M almost got there ... just do a new face for the speedo, I would think that would be a piece of cake compared to the effort you would have put into getting a new drive gear.

Even simpler soln. Wheel tyre combination is the key.

I know the tyres can affect the speedo but I'd like to keep the current 195/50R15 I have and have the speedometer be within a fair tolerance. I've contacted a few people regarding 3D printing this but it's quite precise and would require quite a fair bit of design. On top of that, there's also the chance it may just melt since the temperatures and environment are quite harsh. For what it's worth, I think the Australian/NZ sportages also used 4.78 too.

Suggest you baseline your speedo error to begin with and report back with specific details of your car.
What is gearbox worm, what is sender gear, what is diff ratio, what are tyres and what is speedo error ?

What is error with 4.6 sender fitted. Is it acceptable ?
(4.6/4.78 is only 4% underspeed error....maybe speedo has overspeed error to compensate)

Maybe a different speedo will give a different result ?
Have you fitted your "Chosen Speedo" yet as it may fix problem fingers crossed ?