NB Speedo - NB6 NB8 and autos

poison · Post by **poison** » Sun Dec 13, 2009 9:13 pm

Sorry to raise this one again, I'm sure someone told me there was a way but I can't find it. Is there a jumper or something on the back of an NB speedo to select between a 5 speed or 6 speed or maybe even an Auto?

Brownie, did you ever find an answer?

brownie · Post by **brownie** » Sun Dec 13, 2009 9:50 pm

Hmmmm,Don't recall,What do you mean by a jumper?

viscarious · Post by **viscarious** » Sun Dec 13, 2009 10:44 pm

I assume he means like a toggle switch? ie how some devices you can select to run on 140V or 250V via that little brown slide switch?

poison · Post by **poison** » Mon Dec 14, 2009 12:42 am

Indeed. It seems unlikely that Mazda would make 2 different dash clusters
depending if they were for a 5 speed/6 speed or auto etc. So I am assuming
there must be a jumper (Wire link) that can be soldered in place to make the
change between final drive ratios so that the speedo reads correctly.

I'm sure someone told me it was possible but that may be my amazing memory
in action again...lol.

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sprsta · Post by **sprsta** » Mon Dec 14, 2009 7:20 am

wouldnt the sender unit on the gear box do that?

Timmo · Post by **Timmo** » Mon Dec 14, 2009 12:45 pm

I would think so- Why worry about the complexity of trying to work out speed from gear ratios when you can just measure the speed/RPM of the output shaft and multiply it by the wheel circumference?

sprsta · Post by **sprsta** » Mon Dec 14, 2009 7:16 pm

id say the auto and manual would be different wouldnt there be a hold/od light on auto then the sender would compensate for the five/six speed

but this is all guess work but seems logical to me

maby call mazda and see if there is a difference between senders?

however i know you can jump points behind a silvia speedo maby a mx5 could be similar
http://forums.freshalloy.com/showthread.php?t=124389

poison · Post by **poison** » Mon Dec 14, 2009 8:42 pm

I have 2 speedo's one white and one black original, they read differently so
that puts the solution in the unit itself. I think it is a 5 speed / 6 speed
thing, can someone confirm that the NB 1600 sometimes came with a 5 speed
not a 6 speed?

Indeed Sprta you're probably right, I didn't look at the speedo itself. That
said I don't want to make any mods unless I am sure. These baby's are not so
cheap.

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Habanero666 · Post by **Habanero666** » Mon Dec 14, 2009 8:51 pm

I can confirm that the NB comes with a 5 speed. It has a black sensor.

Hope this helps Poison.

poison · Post by **poison** » Mon Dec 14, 2009 9:46 pm

Ahhhhhhhhhhhhhhhhhhhh, thanks, although mine also has a black sensor.... but
given the two speedo's read differently from the same sender most likely
means the change is at the speedo end. I have managed to make the adjustment
via an electronic device, but it bugs me as there should be a way to do it
directly.

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KSCRIM · Post by **KSCRIM** » Mon Dec 14, 2009 10:17 pm

I think you will find that the speedos are set up for the different diff ratios used for the 1600's (4.3) and 1800's (4.1). The sensor is driven from the output shaft in the gearbox, so the number of gears dosn't come into the problem. There are 2 different sensors available for fitting to the gearbox to accomodate diff ratio changes. I don't know if the speed sensors match the diff ratios correctly though. If not, then the trim on the speedo will be to get the speedo inside its calibration range. (guessing slightly here)
There is another diff (3.95??) used in some cars, (MSM turbos?? and possibly the Auto's??) and that would have a 3rd speed sensor ratio.
As always, E&OE

Mark · Post by **Mark** » Mon Dec 14, 2009 10:54 pm

This probably doesn't help, but my NB six-speed has "6 speed" marked on the tachometer dial face. As such, they clearly put a different cluster in 5 and 6 speeds and another different one as well for autos on the assembly line. So rather than just change a jumper setting somewhere on the back of a standard part, they put in the whole pre-assembled part.

Edit - it gets worse for the guy on the assembly line, as not just three types of speedos for 5,6 speed & auto, but also JDM 180kph, metric 240kph, miles, and combination kph/mph markings in some markets. So when a car rolls up, he's got at least 12 choices of instrument clusters to put in. I wonder if he got paid more than the guy gluing the rear view mirror on the windscreen?

As far as the sensor driven from the output shaft, it's driven from a gear at the end of the shaft. Whether that's a standard Aisin AZ6 gear ratio that mazda adapted for use, or one supplied to suit mazda's sensor/speedo electronics is anyone's guess. Perhaps it's 1:1, but I doubt it from looking at the schematic.
I think there are 3 known standard diff ratios for NB1.8. 4:1:1 in the 5 speed, 3.909:1 in the NB8A six speed, 3.63:1 in the aussie and possibly NZ NB8B six speed (?). Japanese market models? Who knows for sure - mine seems to be consistent with the 3.909:1 ratio based on GPS verified speed and revs.
I think to get an answer you might need to ask at Miata.net. There's some clued up individuals there who've tinkered with instruments and might be able to steer you in the right direction.