Differential gear ratio with overdrive transm

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Did Ford motor company specify a certain differential gear ratio to be used with the overdrive 3 speed standard transmission which was optional in 1949 and 1950??
 
Yes a 4.10:1 with overdrive and I think a 3.70:1 without. Some run the higher gears with the overdrive with good results.
 
how do I know which one I have if I can't read the number on the bottom?
 
i have been running the 3.73 rear in my 50 since i added the OD and am thinking of going back to the 4.10 as when it shifts into OD around 45mph in traffic it seems to lug pretty hard and get vacuum down pretty low at that speed in the OD.
 
I turned the axle 1 complete revelution and the drive shaft turns 2 complete revelutions. What does this tell me?
 
Jack one rear wheel off the ground, leave the other on the ground. Chalk mark the tire and one on the floor. Mark the drive shaft and rear end. Turn the tire 2 complete turns and count the no. of turns the drive shaft turns. If the drive shaft turns a wisker over 4 turns it's a 4:10 if it turns close to 3 and 3/4 it's a 3:71 ect. Walt
 
It's a 4:10 You have to turn the rear wheel 2 turns on account of the spider gears. Walt
 
walt would you not get the same if you turn wheel once ???,,,i tried & got wheel turn once to mark & drive shaft 3.3/4 so i assumed i had 3.78 ratio
 
Trev, If you actually saw the driveshaft turn 3 3/4 times while you revolved one wheel only once, you have a 7.50 diff ratio. Did you ACTUALLY SEE the driveshaft turn 3 3/4 times?? oHIo Jim
 
Years ago I had a '54 Ford 6 with O.D. It had a 4.10 originally, but I put a 3.31 from a '51 Fordomatic in it. I liked it a lot. The neatest part was passing somebody with your hand on the 3 speed tree obviously in second gear at 80+ mph. Got a lot of amazing looks. oHIo Jim
 
If both wheels were off the ground, both "might" have turned the same number of revolutions altho that rarely happens unless you have a limited slip rear. Brian G. NY
 
Not sure if it was 100% but those I was involved with were 4.11.



However there was a lot of swapping done pre-sale so there were a certain number of non-OD around with 4.11 and a lot of OD with 3.68.



The OD was .7
 
From the factory, these cars had 4.10 gears with OD and 3.73 without.



Norm
 
Thank all who responded to my o.d. question. Car is still in storage (Iowa) and will check it out when I get it out. Don
 
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