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Last year when my gearbox was restored (2000 spider) the drive for the speedometer was bad so it was changed. We could not find a new one so this one was taken from another Alfa model, not sure which one. The problem is that it shows way too much speed. At a correct 100km/hour it shows 125km/hour. My question is how many teeth are on the correct 2000 drive? And secondly, where can I find one, preferably new?



spedometerdrive.jpg
 

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Wouldn't you need to change the drive gear - as well as the driven gear - when changing the ratio?
 

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The drive gear and input gear must be a matched set. Simply inserting an output gear from another type of Alfa will generally not work. Each set is for a specific rear-end ratio. You should check the 102 parts book, and then compare the part numbers found in other type Alfas. SOME of the transmission parts for the 102 are different than other Alfas.

Having said that, I have found that all 102 speedometers read about 10% faster than reality.
 

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The whole system is mechanical and speed in the gearbox is proportionally translated into the reading on the speedometer. Therefore, logic tells me that if your gear gives you a 25% higher reading of speed on your speedometer, that you need a 20% reduction in the cable spinning to the speedometer, and thus that you need 20% more teeth on the gear going into the box. You have 21 now, and the correct number is likely 25 or 26. Having said that....that would make the gear substantially bigger, as the distance between the teeth need to be constant. Would it still fit? Are you sure the problem is not on the other (i.e speedometer) side? I read somewhere that mechanical speedometers work with a magnet that creates a torque when turned around by the turning cable (due to the speed of the car). This counteracts a torsion spring in the speedometer holding the needle at 'zero'. Is the torsion spring maybe too weak?
Gr., Pieter
 

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I’ve got a fresh transmission in the shop. I’m jammed for time right now, but can eventually remove the speedo drive and count the teeth.

I think there were three different rear end ratios offered during the 2000 production, although only one is commonly found. Each rear end ratio would have used a different speedo drive to ensure the instrument matched the actual speed of the car.

Jay has occasionally remarked that using a mismatched gear set usually results in something breaking.
 
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