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i have a rear end out of my 70 fj40 how do i find the gear ratio? i made a mark on the drum and another where the drive shaft hooks up but when i do 1 complete turn on one i also get 1 complete turn on the other one. what am i doing wrong? whats the correct procedure?
 

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it should be cast into the 3rd member housing. Look at the flange where it bolts to the housing. If it is a 70 FJ-40 with stock gears it will be 4.11 any way.
 

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Make a mark on the tire and turn the tire one full turn, the driveshaft should turn about 4 times (indicating 4:10 gears). If it turns more than that it will be your approximate gear ratio. (Almost 5 turns will be 4:88, etc.)
 

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if both wheels (drums in this case) are turning at the same speed, then count the # of pinion rotations that makes BOTH the tires rotate once.. if it's an open diff you can hold one tire still, then turn the pinion and count revs to rotate the one free drum TWICE.. both of those counts at the pinion will give u your gear ratio..
 

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First off, the gear ratio is 4.11, however if you really wanna double check, pull the diff cover off and count the ring & pinion teeth. Then divide the # of ring gear teeth by the # of pinion teeth.

Example: 37 ring teeth divided by 9 pinion teeth=4.11
 
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