Re: Alfa 75 diff change
My conclusion re having a 3.54 diff is still an assumption in that, as far as I have found ou,t you can only tell what diff you have by looking inside. I worked out I'd had a diff change through examining speed in gears charts, and using GPS to check my true speed, and with a difference of 16% that equals 4.1/3.54.
I've bought a speedo converter in a kit, but so far I have not been able to get it to function at all, despite it being advertised as "suitable for all electronic speedos". Still working on it though.
Your problem sounds completely different, but presumably related to electronic matters rather than a straight mechanical cause in my case.