Early ring & pinion

[Tom Endy]

At the beginning of production the R&P ratio was 370 (10-37) and used a pinion gear that did not have threads on the sleeve. The threads were on the drive shaft and the two pre-load adjusting nuts were much smaller than those used in later production.

A service bulletin issued in March 1929 (page 327) changed the R&P ratio to 378 (9-34). For a number of years it was my assumption that the SB was addressing the change over to the later style R&P with the threads on the pinion sleeve. However, this apparently was not the case as I recently disassembled a rear axle assembly and found the early style R&P, but with a 378 (9-34) ratio. See photos if they appear (the pixels are high, if they don't post I will re-size and try again).

The question:

Since there is no service bulliten that I could find that indicates the change over to the later style R&P and drive shaft, does anyone have knowledge of when this change actually occurred, and was it documented?

Tom Endy