Differentials

The accompanying Interchange Chart, and Gear Ratio Chart, show the stock ratios available and possible swaps. The keys to interchange are driveshaft flange, axle spline (with outer wheel bearing diameter), and inner CV joint bolt pattern (for 86-92). For 79-85 entire axle assembly swaps, be sure not to mix drums, shoes, brake backing plates when mixing the 79-80 style with the 81-85 style, or backing plates when mixing 81-83 with 84-85.

YEARS PART NOTES
79-85 (12A) Complete axle assembly Brake line threads changed in '81, shoes drums, and adjusters are much better 81-85. Driveshaft flange changed in '83.
79-83 (12A) non LSD Bare axle housing Interchangeable
84-84 (12A) non LSD Bare axle housing Interchangeable
79-83 Bare axle Interchangeable
81-83 All Interchangeable except must match w/LSD and driveshaft / flange (larger in '83)
79-83 3rd Member Interchangeable except must match driveshaft and flange (larger in '83)
84-85 3rd Member Interchangeable
86-92 All non-turbo 3rd Member assembly Interchangeable
86-92 Turbo into non-turbo 3rd Member assembly Must re-drill and machine pinion flange for non-turbo driveshaft bolt pattern, and use Turbo halfshafts
89-92 4.3 viscous LSD into non-turbo 3rd Member assembly Bolt-in, must use LSD stub axles

 
RX-7 Stock Rear Axle Ratios
Year / Model Ratio
79-82 3.909
83-84 12A 3.933
84-85 13B GSLSE 4.076
85 12A 3.909
86-88 5-spd All 4.10
86-88 Automatic 3.909
89-92 Turbo 4.10
89-92 non-turbo, non LSD 4.10
89-90 non-turbo, viscous LSD, "GTUs" only 4.30
93-95 w/manual trans 4.10
93-95 w/automatic trans 3.909
 

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