How To Find Gear Ratio??

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Wilnutt

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I was at Cophers, found an 8 1/4 from a 73 dart.... how do you tell the gears, i assume by teh tag...i found a tag on teh outside, with numbers 2 2 on it..what does this mean, is the gear tag on the inside?
 
Mark a brake drum with a marker or tape so you know where it started. Then rotate the yoke of the differential. Watch and count how many times the wheel/drum revolves. If it takes 3 1/4 turns of the yoke to make the wheel rotate one full revolution, then you have a 3.25 (actually 3.23:1) gear. Get it? If the yoke turns 3 1/2 times, then you have a 3.55, and so on.
 
sometimes the tag will say it my 7.25 said that i had 2.76 gears but when i opened it up it had a real detroit locker and then i checked it and it came out to be 3.91 gears. so i would think that the best way is to mark it and turn it. if i wouldnt have i would have thought i had 2.76s until i drove it. hope this helps some
 
This might be a stupid question.,but does this method work with any rearend for any make?
 
If you're going to count tire rotations make sure that both tires are off the ground. If one tire is left on the ground and you've got a non-posi diff. the tire off the ground will spin at twice the speed that it should when you turn the pinion. This is because the differential planetary gears are, Crap I can't remember the term.

terry
 
IMO, change the rears gear oil and while your at it, look on the ringgear for the stamped ratio.
(When was the last time the gear oil in the rear was changed?)
 
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