gear ratio

[Heavy Duty]

I read on the forum that if I took the plugs out of differ. and painted the ring gear tooth, rotated the ring gear once, counted the teeth on the ring gear, used the a chart it would give me the ratio of my rear end. I did it twice came up with 44. Problem is that is off the chart low. No known ratio that low. Where did I go wrong?

[jimTN]

What year car did the rear end come from, was it hot-rodded? Count again. There were two stock rear end ring gears that would fit a car that had 40 or more teeth, the 9:40 used with 60hp v8s and the 41, a 4:56 ratio used with commercial 4cyl 41 trks.

[rotorwrench]

First we need to know year of manufacture and what type vehicle, ie car, truck, etc.

[Heavy Duty]

It is a 1938 Ford roadster

[rotorwrench]

So it should have a prewar banjo rear axle then. I've not had any aftermarket gears cross my path yet with that high a tooth count. The cars with 85 HP generally have the 3.78:1 with either the 10-spline or 6-spline pinion in that time frame. These are 9-34 tooth count. The 4.44:1 ratio was used with the V8-60 in passenger cars and the 4.55:1 was used in commercials with V8-60 but the highest tooth count is the 9-41 for the commercials.

Folks loved to use the 4.11:1 when running Zephyr transmission gears but they were only 9-37 tooth count. Ford usually stamped the count numbers on the web of the pinion flange of the center section that was the tooth count that came with the axle housing from the factory but there has been a lot of water under the bridge since those days.

If it's non original with an open drive rear axle then it could be about any ratio.

[Heavy Duty]

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Thanks gents. I found the problem. In 82yrs I havn't learned to count. 41 teeth = 4.55.