Reply To: Rear axle ratio on a 1933 Twelve

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Hi Scott,

I assume you’re speaking of the small twelve (Model 1236, 429 cu in) chassis. (The big (462 cu in Model 1242 and 1247) 1933 twelves did not have worm gears, but torque arm hypoids, with ratios of 4.58:1 and 4.82:1, depending on wheelbase and body style.)

The worm gear ratio on my 1933 839 7-pass sedan was 4.29:1, although I have replaced it (factory-approved process, described in an original P-A Company service bulletin) with a 1934 hypoid assembly. I have the Timken prints for this worm gear and wheel set. They were supplied in ratios from 2.78:1 (believe it or not!) to 4.57:1 for other cars. In addition to the 4.29:1, the 1236 may have used a 4.43:1, don’t know.

Cheers,

Bob