Trigger Wheel On Differential for Speedometer
 

Hey everyone, I did some searching trying to find a trigger wheel to put on my differential but I am not having much luck. Has anyone here done this with a 1.8 diff before?

For background, I have an NA that I am doing a 6-speed swap in with a 3.3 ring and pinion for the diff. I would like to have an accurate speedometer and I saw greg petters do an NB gauge cluster swap which I am heavily debating doing for the electronic speedometer. I think this would also be good incase I decide to ever switch up the transmission and differential combo as well.

https://www.thecarpassionchannel.com/clusterswap/
This is the video and write-up I plan to follow to accomplish this, but he kind of skipped over the trigger wheel part.

Umm, just replace the sender gear with the correct one for final drive ratio? Won't work with an NA cluster, but will with the NB.

I guess I haven't dug too deep yet, but does anyone sell a speedo gear that would fit 6 speed geared for a 3.3 diff? I just assumed since mazda never made one besides a very rare few that I wouldn't be able to get the proper gear for the sensor.

You’re correct, there isn’t an NB speedo drive gear for a 3.3. The fabled diesel B series truck that came with them *might* have had a drive gear that would fit in an NA cable housing, but that would be a very long shot. If you google around, I think there is a table of what Speedo gear came with what ratio. The driven gear on the transmission output shaft was the same across 5 & 6 speed gearboxes and all diff ratios; only the speedometer drive gear tooth counts changed.

All this to say, I’ve got an NA 6sp/3.6 final drive and have found the 3.9 speedo drive is actually very accurate. It’s been long known/confirmed the cable speedometers read a bit high from the factory. So you could probably get away with a 3.6 cable drive setup. I promise this hasn’t all been a sales pitch, but I do have a brand new 3.6 cable drive speedometer sender I don’t need since deciding to keep the now-very-accurate 3.9 sender for my 3.6 diff.

Do with this information what you will. The electronic Speedo swap seems excessive even if yours ends up reading rather high. But maybe that’s just me ¯\_(ツ)_/¯ However if you really did want to do that route, just throw an NB electronic Speedo gear drive in your NA and use a converter box to make a digital Speedo read accurately. Much easier than a tone wheel on the pinion flange!

The 6-speed I have is a 3.9 sensor. As I was looking for some other options I did realize I could probably just use the 3.9 speedo sensor and like you said use a converter box since I would have to anyway if I got a trigger wheel. I would like a pretty accurate speed and I could not find a cable-driven 3.6 anywhere so I kinda gave up on that idea. Out of curiosity, how much would you sell it for? Still thinking about doing the cluster swap, but using the mechanical could save me a lot of time and effort also and leave room for my other projects.

I dug it out and, my apologies, but its a 3.9 gear. I'm now very confused about what sender is actually in my car. Carry on.

Ah, that's unfortunate. Well if anyone else who stumbles upon this thread has a 3.6 mechanical sensor they would sell I would be open to that option.

As for the original thing, if I do an NB gauge cluster swap and use my 3.9 sensor do you guys think a Dakota digital can correct for that? I know there is a certain range in which the speed can actually be corrected.