rearaxes and speedometer 245

No, the speed pickup is done by a toothed wheel on the differential carrier, which effectively turns the same speed as the tires. These pickup wheels do have different numbers of teeth depending on whether the car had ABS or not.

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As I remember, there are different pickup wheels whether the car has a limited slip differential or not, but these wheels have the same number of teeth. There are a different number of teeth on the wheels if the car originally had ABS. The teeth difference is obvious. There wasn't a change in the number of teeth as on the 700 series in '89.

That's what you do if the 240 is from 1985 model year or earlier.

Depends on the specific car. The 92-93 240 with ABS has a different reluctor ring (the part that actually induces the speed signal). This is matched with a differently configured computer (which also drives the ABS). So, you need to be sure that the rear axle has the correct ring or a variety of helpful tools won't work properly, things like the speedometer, odometer, cruise control and ABS.

I know this because I'm about to have the correct reluctor ring installed on the replacement axle on my '92 245, which originally came with limited slip (which broke).

HTH

-pk