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I recently swapped the gearbox in my NA6 with an NA8 unit. All works well, but now speedo reads about 10k high, ie reads 100 when doing 90 according to gps. Does anyone know if the gear on the gearbox end of the speedo cable can be changed to correct this. Everything else is stock standard, diff, wheels and tyres.

many NAs indicate 105kph when actually doing 100kph - aftermarket error correction is available, but experimenting with OEM parts might get it to 5kph or less difference.

Do you have any more info on aftermarket correction? What OEM parts are you referring to which may affect this?

91mx5 wrote:Do you have any more info on aftermarket correction?

What OEM parts are you referring to which may affect this?

Try Google, but I know Carco in Canberra fitted one of these to a forumite's car.

Assuming you only changed the GB & not speedo cable as well, may be try finding out (search) if the speedo cables are interchangeable. Changing the gear at the GB end of the speedo cable may be possible, but usually those sort of cables don't disassemble easily, if at all. Hence, the suggestion to try changing the cable, if feasible.

I used the original speedo cable. Cheapest option no doubt will be second hand NA8 cable. Thanks for your suggestions.

There are two (2) speedo Drive gears avalible from Mazda
One is 23 Teeth the other is 22 Teeth
also one is red the other Purple
There is one 10mm head bolt thatholds it into the box
best to remove and see what you have

From memory, mine is purple. To slow speedo down, I assume I would need 23 tooth gear. Is the gear attached to the cable with a grub screw? I'll have a look at the on-line parts manual in MX5cartalk and see if shows how it couples with cable.

93_Clubman wrote:

91mx5 wrote:Do you have any more info on aftermarket correction?

Try Google, but I know Carco in Canberra fitted one of these to a forumite's car.

here's where (a third of the way down the first post) i read about the "electronic speed corrector":
viewtopic.php?f=57&t=35718

Electronic speedo corrector will be no good as it is a mechanical drive (cable).

Just as Russelb said, undo the cable from the box (thumbscrew) and take the na8 sender out (one 10mm head bolt) and put in the one from the na6 box. The boxes are the same with minor internal differences so it just swaps right over.

Cheers,
Tim

apparently the "electronic speed corrector" was used on an nb8a, so that suggests they're not mechanical from what you're saying

93_Clubman wrote:apparently the "electronic speed corrector" was used on an nb8a, so that suggests they're not mechanical from what you're saying

I am struggling to remember which year/model they switched over to the electronic speed sensor but I am pretty sure all NA6s were cable dríven (which is what the OP has). Might be the case for NA8s too.

Think all NBs were all electronic speedos.

Can anyone else confirm this?

Thanks Les - certainly sounds that way from what Tim said.