Checking ratio in a 9inch?
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New User
Joined: May 2005
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Checking ratio in a 9inch?
So we lift one side of the truck on jackstand. Turn the tire, the drive shaft turn 1 1/2 turns... doesn't make sense, I never heard of a 1.50 gear ratio. Anyway, we look the tag up and gear ratio is apparently 2.75. So, what the hell are we doing wrong? We usually do this with Dana axles to get an estimate of gear ration, why is it not working with the 9 inch? Looking at it we're only getting half of 2.75...
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Frank, believe what you see on the tag, they don't lie.
If you really do have a 2.75 ratio, you should have got 1.375 turns on your driveshaft for one turn on the wheel because the other wheel wasn't turning.
Jack one wheel up and turn it exactly 8 times. The driveshaft should turn exactly 11 times.
If you really do have a 2.75 ratio, you should have got 1.375 turns on your driveshaft for one turn on the wheel because the other wheel wasn't turning.
Jack one wheel up and turn it exactly 8 times. The driveshaft should turn exactly 11 times.
Post Fiend
Joined: Mar 2002
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From: Bonita Springs FL
The differential spins at the rate BOTH tire spin. If one tire is stationary, and you spin the other tire once, the carrier has moved 180 degrees. So if you're going to do the jack-on-tire-up method, spin the tire twice and then count the driveshaft revolutions.
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Makes sense, differentials are tricky at first... I also found interesting when taking the Bronco 9 inch out that we didn't see the gear ration or teeth count on the ring gear... there were markings, but nothing clear and simple..
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