Technical Which speedometer gear?

[marcus550]

My 5-speed gearbox somehow sheared the speedometer gear clean off. I can't remember if this was my original 500F gear or if it came with the complete 5-speed syncro-transmission w/126 bell housing. So, I don't know the origins of it. The body of the speedometer drive says 4251622, but when I look this up at parts suppliers, it is always described as a 15 tooth. Mine is (was ) a 16 tooth. The Lusso speedometer always seemed to read correctly so I have no desire to change. But...which speedometer drive do I need? I can't replace like # for a new one, as they're one tooth different.

Maybe telling is the teeth on my original gear are noticeably worn down compared to the pictures of new ones. The gear on the transmissions looks fine.

 

[marcus550]

I'm back to my old post on this speedometer gear. I installed another 16 tooth in this 5-speed tranny. It lasted two years before it was worn down to nothing. Is this due to it being 16 tooth vs. 15? I still don't know the correct gear for this mongrel. Has anyone seen this kind of wear on a speedo gear?

 

[the hobbler]

I'm back to my old post on this speedometer gear. I installed another 16 tooth in this 5-speed tranny. It lasted two years before it was worn down to nothing. Is this due to it being 16 tooth vs. 15? I still don't know the correct gear for this mongrel. Has anyone seen this kind of wear on a speedo gear?

View attachment 477908

If your 5-speed gearbox is based on a Fiat 126 gearbox (synchro on 2 + 3 +4 and no need to double-de-clutch on down-shifts) then the speedo drive SHOULD have 15 teeth. If however your gearbox is based on a 500 'box (dog-clutch--NO synchro) then the speedo-drive should have 16 teeth

I'm back to my old post on this speedometer gear. I installed another 16 tooth in this 5-speed tranny. It lasted two years before it was worn down to nothing. Is this due to it being 16 tooth vs. 15? I still don't know the correct gear for this mongrel. Has anyone seen this kind of wear on a speedo gear?

View attachment 477908