9" rear end
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Junior User
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9" rear end
My friend just bought a 9" rear end and doesn't know what size gear ratio is in it. Is there a way to find out? I thought you could turn the axle and count how many times the driveshaft turns in one axle rotation. But i am not sure. Any help would be appreciated.
Elder User
Joined: Feb 2004
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From: Oregon
The easiest way to check the differential gear ratio in any rear wheel or four-wheel-drive truck is to lift the rear end of the vehicle with a jack and physically rotate the rear tires one complete revolution while counting the number of revolutions that the driveshaft makes. If the drive shaft rotated just over four times, your differential gear ratios would be 4.10:1, etc.
Those aren't my words, but they might help
Those aren't my words, but they might help
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Junior User
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Originally Posted by andym
Why? Didn't that work?
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Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Then either you're not watching closely enough, you have a previously unknown 0.50:1 axle ratio, or something is broken inside your 3rd member.
Sorry to be a smartass, but the method described is a common way of determining gear ratio - it just works.
Sorry to be a smartass, but the method described is a common way of determining gear ratio - it just works.
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Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
If one drum is turning and the other is not, only spin the one drum half way around. Or once around, and divide the number of pinion revolutions by two.
If both drums are turning in the same direction, spin the drum once around, and the number of pinions revs is your ratio.
If the drums turn in opposite directions, you'll have to hold one in place.
That's why it's easier when it's still on the vehicle. But not impossible, of course.
No luck finding the tag, either?
If both drums are turning in the same direction, spin the drum once around, and the number of pinions revs is your ratio.
If the drums turn in opposite directions, you'll have to hold one in place.
That's why it's easier when it's still on the vehicle. But not impossible, of course.
No luck finding the tag, either?
Post Fiend
Joined: Jun 2002
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From: Atlanta GA
Ford4x4trkn,
I had the same thing happen when I tried to do my rear end ratio that way. I think maybe without enough weight on one side it happens. I just pulled the center carrier and counted teeth.
Very easy to do on the 9". Just remove both axles and be careful not to rest the axle on the axle seal or to tear it with the axle spines.
With the axle out of the truck it is the perfect time to change fluid and have a look at the gears and such and to clean out the axle tube and the vent tube.
I had the same thing happen when I tried to do my rear end ratio that way. I think maybe without enough weight on one side it happens. I just pulled the center carrier and counted teeth.
Very easy to do on the 9". Just remove both axles and be careful not to rest the axle on the axle seal or to tear it with the axle spines.
With the axle out of the truck it is the perfect time to change fluid and have a look at the gears and such and to clean out the axle tube and the vent tube.
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