850 Differential Compatability (archive)

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Huge can of worms, but I'll take a stab. In short the e32 differential works, but BMW and others will tell you it won't. At $600 vs. $2,000-$3000, its worth some digging. Here's the circuitious path I traveled to find the answer in the world of BMW parts matching:

(1) According to BMW, "no," the e32 differential unit and housing will not fit e31s. BMW's internal ETK parts system does not recognize the e32 (PN 33 10 212 462) or any other differential unit as compatible with the e31's (PN 33 10 1 213 136). Same for the housings, the parts numbers don't match between e31 (PN 33 1 212 988) and e32 (PN 33 1 212 370).

(2) However, a search of shared differential components for the e31, e32, and e34, shows that seals, gaskets (including rear cover), and internal parts are shared, yet not input shafts (different flange pattern) and rear covers (different suspension mounting points).

(3) Even Worse, I've found that available used e32 differential housings are marked with PN 33 1 212 371 (not 370 as specified in the BMW parts system). At this point, most people abort and assume, as BMW parts counter people, that it will not fit. No one at BMW has been able to explain the 371 number present on early 3.15 750 differential housings.

(4) From my first hand experience, the 371 casings fits the e31. The casing shape is the same, accepts the e31 cover, and has the required two front right side bolt holes for the suspension mounting point. All you have to do its keep your rear cover and input shaft. Otherwise its a bolt in option.

(5) From discussions with others who deal with hand's on swaps or rebuilds regularly, the e32 and e34 (540, M5, 535) differentials will also work as long as you change the covers and input shaft.

Hope this saves others some time and clears up a clearly confusing parts issue. Happy hunting.

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