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Old 08-19-2014, 02:00 PM
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uberwasser uberwasser is offline
1979 & 1985 300D's
 
Join Date: Oct 2012
Location: Tucson, AZ
Posts: 1,097
The diff will indeed bolt in. They should be the same, externally.

However, the 85 model year in particular has rather "tall" gearing. Namely, it will have a ratio of 2.88:1.

Your '79 N/A car has a ratio of 3.46:1

That is a substantial difference and you will notice dramatically decreased acceleration off the line, especially with no turbo to help with the get up and go, compounded by the fact that your car is likely equipped with the 722.118 auto, many of which are set up to start in 2nd gear unless floored from a start, or manually shifted.

If you want some more top end, or simply a quieter running car at highway speeds, you may look in to swapping a diff from a turbo car anywhere from '81 thru '84. These have a ratio of 3.07:1 and this might be more livable.
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