[VAC] Re: Vintage Puller

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx>]

I think 4.10 is just fine. Perhaps even 4.54 would be more appropriate
depending on the load you want to pull. My vintage Ford F-350 has a 5.13
axle, and a 390 under the hood. It gets about 9 mpg if I keep it down to
50, less if I really load it or drive it at 65. With the 15 gallon tank
in the cab it almost pauses automatically for each gas pump seen.

I don't think that 3.90 gears would have a measurable effect on mileage
or performance. I changed my '98 F-150 from 3.08 to 4.10 and the gas
mileage is the same within experimental error (unless I use the extra
acceleration too often). Even if the change was perfect and the gas
mileage went from 10 to 10*4.10/3.90 = 10.51 mpg, that half mpg change
would take a long time to recap the $500 it cost to get the gears
changed. 5 gallons per thousand miles, so it would take at least 50,000
miles to cover the cost of the gear changes at the best, likely there
would be so little change in gas mileage to make it not detectable.

A far easier way to make minor changes in effective axle ratio is to
change tire sizes. An effective change from 4.10 to 3.90 takes only a
change in tire diameter from 30 to 31.5" probably changing from a 265 to
a 285 radial cross section. Two tires are a lot cheaper than a set of
gears, installed.

But for a guy who couldn't pay for a spare, isn't talking changing gears
or tires beyond financial reason?

Gerald J.