On the BMW mailing list Curt Ingraham was asked:

Does anyone know the gear ratio of the final drive on the automatic
transmission equipped '73 2002?

Most likely: 3.64:1. Less likely: 3.90:1.

Are there any identifying marks on the final drive that would
indicate its gear ratio?

Yes, although they can be hard to see, even with glasses, and even after
scraping off the crud. Two numbers are stamped into the side of the case near
the front, probably on the port side, such as:

40 11

These are the numbers of teeth on the ring and pinion gears, and their ratio
is the gear ratio of the unit. For this example, 40/11 = 3.64, identifying this
as a 3.64:1 unit. Some possible ratios are:

37 11 - 3.36:1
38 11 - 3.45:1
39 11 - 3.54:1
41 10 - 4.10:1
37 9 - 4.11:1
38 9 - 4.22:1
35 8 - 4.38:1
40 9 - 4.44:1
38 8 - 4.75:1
35 7 - 5.00:1
37 7 - 5.29:1
41 7 - 5.86:1

The additional marking "S 40" or "S 75" identifies a limited-slip differential
with a 40% or 75% locking ratio.

Curt Ingraham
'72 tii
ingraham@ssl.berkeley.edu