Hi, new to this forum. We have a 1984 245 manual trans. Trying to get to classic plates-one more year. OD recently went bad. Our long term Volvo mechanic purchased a used OD unit and rebuilt it.Not sure of theyear this used unit was from. Mechanic says he used our orginal speedo gear. Now OD works great. However, the speedo at 20mph is off buy approx. 3-4 mph, the faster we go the farther off the speedo is. From 50+ the speedo is off by approx. 8 mph. This was measured by GPS and by pacing another car. Nothing else ws changed. Also, this has affected the odometer and trip meter. They are off by a couple of miles. They will read 25 miles to work but work is approx. 28 miles. Really makes the gas milage look bad. Our mechanic does not know why this has happened. Any ideas?
Thanks for any help.

 

Update: We just got a call from the mechanic. It appears that there is a difference in the OD units between the sedans and the wagons. It appears that he replaced our wagon unit with one from a sedan. So he thinks this is why the spedo is off and the car feels a little sugglish. He is going to replace the gears. Well let you know if this works.