Once again I'm diagnosing the kid's '91 240 from 3000 miles away. He recently suffered a seized differential - not sure why, but he dealt with a local foreign car shop who found him a new rear end, *allegedly* from a '91. A few weeks afterward I get the report that ever since that repair, the speedo "doesn't work." It seems to indicate a fraction of the real speed, but far too great to be a simple gear ratio difference. Sounds like it indicates maybe 30-40% of true speed. At least he has a tach to go by, and he remembers the automatic's shift points so he's not flying completely blind, but it would be good to get the speedo functioning properly again. I'm puzzled by the fractional speed indication - if the speedo pickup on the diff cover was broken, or its cable was broken, seems like there would be no speed indication at all. I realize the pickup is a proximity sensor of sorts, so I wonder if the gap between the sensor and the ring gear is too great with the new diff.

Anyone care to share thoughts or experiences?