Packard Forum Index » Pre-War (1899-1942)

Pulling the rear differential cover to clean, I found the following stamped on the ring gear. The Service Parts List being issued in 1927 did not have the part number I saw. Stamped in the gear was the following:
141571-13-57 Packard 6-28.
Does this tell me I have a 4.38 to 1 gear ratio? I assume the 6-28 is June 1928 mfg date.

Looks like you have a 57 tooth ring gear and a 13 tooth pinion which gives a ratio of 4.38 ( 57/13 = 4.38)
Count the teeth to confirm.
This corresponds with the drive ratio for a 4th or 5th series six cylinder open car.
The part number in the book is for the differential assembly not the ring gear.
The same ratio was also used in some of 3rd, 4th & 6th series eight cylinder cars

Thanks for the confirmation. I have a 1928 model 526, 6 cyl 5 passenger sedan. The standard ratio that year was 4.69 to 1 according to the parts book. Does this mean that with my ratio I can get a faster top speed with lower rpm? I am told that I should try to keep my engine speed below 2500 rpm so as not to tax the motor and transmission. Does my ratio do better at this than the standard ratio?

Yes, slightly. You'll have 4.38 engine revolutions per revolution of the rear wheel versus 4.69. Measure the circumference (or diameter x pi) of your rear tires and do the math to get rpm at various mph.

Or, if your tire size is the same, use this chart from the Packard service letters. Even if your tire size is different you can see the relative differences between the 4.38 and 4.69.

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As OD says the difference will be slight.
I had to change the 4.69 :1 ring gear and pinion unit in my 1929 633 sedan due to wear and the only replacement available was a 4.38 : 1. I was a little concerned that the higher ratio would reduce hill climbing but it was not a problem. The comfortable maximum cruising speed increased slightly to about 48 mph and I could not detect any change in hill climbing.
Overall a small improvement.
It takes a much greater ratio change to significantly increase the cruising speed but it will be at the expense of top gear performance on steep hills. Both 4.69/1 & 4.38/1 would be well matched to your car.