I don't usually get stumped too much by automotive parts but I have a head scratcher going on now. I thought I knew how to check the gear ratio on rear ends, but I seem to have a 1940 ford two door deluxe rear end with a ratio of 1.77:1 ???? can someone tell me what I am doing wrong or is this a special rear end of some sort??? i am sure its me doing something wrong. the story behind the car was it was ordered by the millidgeville Illinois ford dealer as a police car, it had the mercury motor and etc but when it showed up at the dealer it was a two door instead of a four door. the guy I bought the drive train parts from was the grandson of the original owner of the car when it was new. I did the single turn of the drum method and I did a 10 turns of the drum and came up with the same numbers. my brother did the same with the same results as did my young nephew, and you know how youngsters know it all!!! anyone out here in hamb land that can set me straight??? thanks for any info you have.
turn drum once, count revolutions of the input shaft (pinion) how many times it turns is the ratio. Use a piece of tape as a flag. I don't see the characteristic larger axle housing of a Columbia O/D. this should work unless something is broken.
The bottom rib of the center housing should have numbers stamped giving the ratio.39-9=4.33,37-9=4.11,34-9=3.78 & 39-11=3.54.But gears could have been changed over years.
Look at the under side of the center section of the rear end. Clean the grease off of the boss that runs through the middle of it and there should be numbers stamped into the casting. Something like 9 37....witch would be 4:11. Divide the small number into the larger number for the ratio. Yes, I have had one with no numbers stamped into it. Tim
If you jack up one wheel and turn the one wheel while the other is held stationary, the spider gears turn causing the driveshaft to only turn half as much as if you turned both wheels at the same time. The result as J.A. Miller pointed out is that you only count half of the turns. Multiply the result by 2 and you get 3.54:1, the correct ratio. A very desirable ratio, much sought after today.
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