Diff swap- 89 I 5spd getting a 91 Auto iS 4.10...

[JoeyJoeJ0]

I recently bought a 89 325i 5 speed with the obvious open diff... im not completely sure on the gear ratio in the diff because the tag on the diff casing is oxidized and crusted over. I plan on swapping the entire rear end from my 91 325iS Auto over to it, but im worried that my speedo may be off because the iS has the 4.10 LSD... should i worry at all?

[Garageaholic]

no, your speedo sensor is on the differential itself, It senses the output shaft anyway, not the input shaft.