Medium case speedo trigger wheel too small

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The last couple of days I’ve been pulling my hair out trying to work out why the speedo hasnt been working in my E30 racecar project. After swapping clusters and speed sensors in and out of working cars and chasing the wiring, i couldn’t figure it out.

I finally noticed this LSD i purchased and fitted has a smaller trigger wheel than the one in the car i was swapping parts over with. Its only slightly smaller, id say 20mm diameter but it must be enough to not register with the sensor.

Now can anybody please shed some light on this. The smaller wheel must be from another series car? Is there a sensor that has a longer pickup in it that will work with my e30 rear cover?

Id prefer not to pull out and apart the freshly built LSD just to swap over the trigger wheel.