Looks like I get to commit a felony and roll back the odometer on the MG.
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In all seriousness, I documented changing the transmission in my MG a few pages back. The original transmission in my car would turn the speedometer drive gear at 1280 turns per minute, with the speedometer matching this. For whatever reason, in the 1974 1/2 model year, this was changed to 1000 turns per minute.
I could have sent my speedometer to Nissonger(US distributor for Smith's and Jaeger gauges) and had it recalibrated, but that's quite expensive. It would have been well over $300.
The easier and less expensive alternative, however, is to simply change the speedometer. 1000tpm was used on MGBs until the end of production(1980) however they instrument cluster was redesigned for 1977 with a larger speedometer(among other changes). For practical purposes, what this means is that a 1974.5-1976 speedometer will drop in to an earlier car. The bezel is a different shape, but fortunately that's a very simple fix.
The replacement has 69,000 miles, while my original has 85,000. I thought about rolling up the replacement, but did some quick calculations. My electric drill runs at 20mph(2000rpms). If I connected it to the speedo, I'd have to run for 33 continuous days to get the mileage to match.
Fortunately, the car is mileage exempt.
