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Discussion Starter #1 (Edited)
I am on coming up to the end of a rebuild I am doing. This is from a '65 Mustang with a 7 1/4" rear end. I am stuck on how to set the differential bearing pre load. I am comfortable with setting everything else, but I am not sure how to set the "case spread" and have not found any information that is set in stone on how to do it. This setup does not use shims to set the preload on the diff. It uses screw type adjusters that mate up against the bearing races and drive them closer to the bearings. Any information would be very helpful. Trying to finish this up for a surprise Birthday gift and this is the last thing standing in my way before handing over the keys. :thumbsup:
 

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According to the 1964-1/2 to 73 restoration Guide by Motorbooks, there isn't a 2.80 set for any of the 7.25" differentials. Their list has a 2.83 and a 3.50 for 1965, and 2.83 and 3.08 for 66-70. There is a 2.80 for 1965, but it's listed as an 8" diff.

You can also count teeth to determine what you've got.
Gear / Pinion - Ratio - Part#
34 / 12 - 2.83 - C5DZ 4209C
35 / 10 - 3.50 - C1DZ 4209Z
37 / 12 - 3.08 - C9ZZ 4209A
39 / 14 - 2.80 - C4OZ 4209K
 
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