Boxilar
Member
I'm not sure if this belongs here or in the engine swap forum. I'm trying to figure out the rear gear ratio on my 1964 LeSabre Sedan. The car originally had a a Wildcat 310 (2 bbl 300 cid v8) with a three speed manual. I've swapped in a Cadillac 425 with a Turbo 400 from a 1979 DeVille. I believe the DeVille had 2.70 rear gears, but I'm not certain. My speedometer is reading 25% too fast. Example, at 60 mph it's reading 75 mph. I confirmed this with a cellphone with navigator using GPS. Hunting around, I need fewer teeth in the speedometer driven gear, but I need to know what the rear gear ratio is so I know what driven gear to use. The shop manual said there were numbers stamped on the bottom of the differential housing, but I can't find them. There is an adapter that reduces the reading by 26%, but I'd rather use the proper driven gear if possible. Thanks for any insight,