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Old 06-09-2011, 11:10 AM   #1 (permalink)
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Default Buying a used 8" third member with Posi, how to identify ratio and locker?

Can anyone give me some advice here, I really dont know what I am looking at.

I found a guy that has a few used take out third members with "posi" and I will be asking him if they are a spool or what type of locker but he does not know the ratios he has, he thinks one was an 8th mile ratio and the other was some street ratio, but no tags.

Whats a good way to identify the ratio on a third member thats out of the rear end? Is the ring gear usually stamped?

Does anyone have a decent pic of different types of lockers/limited slip units so I can identify them?
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Old 06-09-2011, 11:28 AM   #2 (permalink)
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Originally Posted by Fstbk View Post
Can anyone give me some advice here, I really dont know what I am looking at.

I found a guy that has a few used take out third members with "posi" and I will be asking him if they are a spool or what type of locker but he does not know the ratios he has, he thinks one was an 8th mile ratio and the other was some street ratio, but no tags.

Whats a good way to identify the ratio on a third member thats out of the rear end? Is the ring gear usually stamped?

Does anyone have a decent pic of different types of lockers/limited slip units so I can identify them?
I know the following for certain on the 9 inch third member, and I believe (but am not certain) that it applies to the 8 inch:

Generally speaking, the higher the gear ratio, the thicker the ring gear. When you have ratios of 3.5 and higher the ring gears are much thicker than a 2.79 set... But for actual gear ratio I would take something to mark a tooth (chaulk, etc) and count teeth and divide.

As to limited slip units, with factory originals it was easy to spot them because the mounting bolts for the ring gear were recessed, on the open units they were flush.

Good luck,
-Rory
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Old 06-09-2011, 12:10 PM   #3 (permalink)
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To explain in more detail like 2ndgen said it's easy to fiqure the ratio especially when the third member is removed. Count the pinion teeth and the ring gear teeth and divide the pinion # into the ring gear #.
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