The Ford Barn

Brian SATX · 06-01-2020, 03:52 PM

Below are two speedo drive gears and cases that have 18 stamped on them. I cannot find anything about them in the Restoration Guidelines. Anyone got any ideas?

ursus · 06-01-2020, 03:55 PM

These were for one of the early V-8 cars and can be used on a Model A if one has a 3.54 ratio rear end.

rotorwrench · 06-02-2020, 10:41 AM

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Just to add: The later rear axles in the V8 era had choices of different gear tooth counts depending on the rear axle ratio and tire size. There is a chart in the 1928 thru 1948 Chassis Parts Catalog otherwise known as the green bible. This chart aids in getting the speedometer to read correctly when changing tire sizes or rear axle ratios. There where quite a few different gear drives and each had the tooth count on the housing. The housings had different shaft bearing locations depending on the size and ratio number of the gear in each unit. They have to have the same tooth count as is on the housing in order to function properly.

The model A didn't have as many choices but there were a few for it depending on rear axle ratio. 19 and 21 were the only two on that chart. The 18 tooth is a good one for lower numerical ratios like the 3.55:1 but I'm not sure if they will work on the model A torque tube.

06-01-2020, 03:55 PM	#2
ursus Senior Member Join Date: May 2010 Location: Oregon Posts: 1,462	Re: Strange speedo drive gear These were for one of the early V-8 cars and can be used on a Model A if one has a 3.54 ratio rear end.

06-02-2020, 10:41 AM	#3
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 17,409	Re: Strange speedo drive gear Sponsored Links (Register now to hide all advertisements) Just to add: The later rear axles in the V8 era had choices of different gear tooth counts depending on the rear axle ratio and tire size. There is a chart in the 1928 thru 1948 Chassis Parts Catalog otherwise known as the green bible. This chart aids in getting the speedometer to read correctly when changing tire sizes or rear axle ratios. There where quite a few different gear drives and each had the tooth count on the housing. The housings had different shaft bearing locations depending on the size and ratio number of the gear in each unit. They have to have the same tooth count as is on the housing in order to function properly. The model A didn't have as many choices but there were a few for it depending on rear axle ratio. 19 and 21 were the only two on that chart. The 18 tooth is a good one for lower numerical ratios like the 3.55:1 but I'm not sure if they will work on the model A torque tube. Last edited by rotorwrench; 06-02-2020 at 12:12 PM.