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Old 01-29-2006, 06:01 PM
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Installing Posi, any tips?

I have an open diff. GM 10 bolt 8.5" 28 spline rear with a 3.73 gear ratio. I just purchased a posi (see pic) for this application. I want to use the existing gear ratio. Can anyone give me any tips to install this? Thanks JD
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Old 01-29-2006, 06:20 PM
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Well, it's not much different from changing the ring and pinion. MAke sure that you have or have access to all of the tools required. An aftermarket posi unit uses different bearings than the stock differental. If the ring gear doesn't go on heat it up a little in an oven. Don't try to make it go by pulling it on with the bolts. Make sure you get a good ring gear run out before proceeding on with the job.
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Old 01-29-2006, 06:48 PM
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1) Use TIMKEN bearings only. This is not the time to try to save a few bucks.

2) replace the pinion gear bearings and seal also.

3) Do the set up exactly "by the book" and

4) use the clearances recommended by your gear manufacturer.

5) Pre-soak those clutches, submerged in diff oil overnight.

6) use assembly lube on those gears so they won't be dry for the first run.

7) use assembly lube on all the bearings so they won't be dry for first run.

8) new gears require break-in procedures as per the gear manufacturer recommendations.

9) when broken-in use synthetic lube, period.

10) as long as the axles are out, replace those seals also, maybe the wheel bearings too.
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Old 01-29-2006, 07:14 PM
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Good advice there.

Number 9 might have also been worded, as below to reduce any possible confusion.

9) After break-in use synthetic lube, period.

ALSO, if this is a new carrier you will want to check the ring gear mounting bolt holes to make sure they are flat by laying a flat file on the ring gear mounting surface and lightly filing to check.
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Old 01-29-2006, 07:35 PM
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synthetic lube ...... ditto's but the posi additive from GM , I believe still applies , before and after break in . Meaning buy two bottles..
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