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Old 05-16-2009, 08:02 PM
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yes 2.56 and around 3.42 and up are different series from each other

the reason is that the ring gears are different thickness for each series and thus the ring gear mounting flange on the unit is in a differnet location to make up for this, because series 4 pinion gear heads are smaller diameter, around 9 teeth,

vs series 3 pinion heads in which are larger diameter and have more teeth with the taller ratios such as 2.56 and 2.73

3.50 is a ford ratio

gm will be 3.31 3.40 3.42 3.73

2.56 is series 3

around 3.42 and up are 4 series
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