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Old 05-31-2018, 03:42 PM   #1
69SCSS
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Test 4 Series Posi

Hey guys, I just pulled my 12 bolt out of my truck and found that my pinion welded itself to the outer bearing (previous owner obviously drove it with no oil) is bad. I knew I had an issue, but thought it was the carrier. I don't see and physical issues with the carrier, so was wondering what I could do to test the posi out and see if the carrier is still good. Anyone have any benchtop tricks? I know the posi was working, just seemed clunky, which now I find is the pinion bearing moving. Was planning on changing the gears, but if the carrier is good, that would save me $450!

Thanks in advance!
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Old 05-31-2018, 06:03 PM   #2
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Re: Test 4 Series Posi

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Hey guys, I just pulled my 12 bolt out of my truck and found that my pinion welded itself to the outer bearing (previous owner obviously drove it with no oil) is bad. I knew I had an issue, but thought it was the carrier. I don't see and physical issues with the carrier, so was wondering what I could do to test the posi out and see if the carrier is still good. Anyone have any benchtop tricks? I know the posi was working, just seemed clunky, which now I find is the pinion bearing moving. Was planning on changing the gears, but if the carrier is good, that would save me $450!

Thanks in advance!
What type of posi do you have ?
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Old 05-31-2018, 06:43 PM   #3
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Re: Test 4 Series Posi

Stock GM posi.
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Old 05-31-2018, 07:28 PM   #4
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Re: Test 4 Series Posi

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Stock GM posi.
So you have the spring type of posi ?.... since the rear end was ran with no oil in it...I would look to rebuild the posi... I am not sure if RMS has a posi rebuild kit for the GM truck 12 bolt posi rear carrier but I think they can be bought, since you have it already out and apart I would spend the money...
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Old 06-01-2018, 12:51 PM   #5
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Re: Test 4 Series Posi

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Stock GM posi.
There are different versions of the stock posi. If you have the gov-loc it's not worth rebuilding.
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Old 06-05-2018, 01:56 PM   #6
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Re: Test 4 Series Posi

If it's stock out of a 1967-72 truck... it will not have a Gov-lock.

It will be a spring clutch limited slip.

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Old 06-05-2018, 03:03 PM   #7
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Re: Test 4 Series Posi

I think the OE posi cases were supplied by spicer. Overhaul parts *might* be reproduced. For a while you couldn't get the clutch disc.

The pinion bearings rely on lubrication thrown by the ring gear. They really suffer when the fluid level is run low.
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Old 06-05-2018, 07:43 PM   #8
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Re: Test 4 Series Posi

Used my press to get the pinion out, and found out why my axle had issues. Looks like the bearing ate the pinion shim. Bits and pieces fell out of the pinion shaft as it dropped out. Oops!

I grabbed an Auburn Posi off Summit, not going to even try to rebuild the stock carrier. My gears thankfully looked clean, so when the rebuild kit shows up with the carrier, it all gets to go back together.
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Old 06-11-2018, 02:45 PM   #9
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Re: Test 4 Series Posi

Picture of your Positraction unit?

I put one axle in the vise pointed straight up and drop the posi onto it. Put other axle in from top and see if you can turn it with just the flange. If you can could use a rebuild. If you have to use a lever of some kind between two opposing lug studs to rotate it, probably OK to run as is.
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Old 06-11-2018, 08:19 PM   #10
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Re: Test 4 Series Posi

Here's some pics. Looks to be an Eaton Posi. It actually looks OK, all the gears are clean and the ring / pinion were clean. Might just see if anyone wants it, could easily be rebuilt, or just pull the posi out and use it as a 4 series open carrier.

Did run into one issue - I can't get the pinion bearing off. I tried my gearing puller a few different ways, even to the point of just pulling the bearing off so it's just the race on the pinion shaft - it wouldn't budge. Probably going to ave to heat it up pretty good and try again. Once that is off, I can press a new bearing on and put the rest of the 12 bolt back together. Going to attack it again tomorrow.
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Old 06-12-2018, 08:48 AM   #11
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Re: Test 4 Series Posi

When putting it all back together, you will need to know the thickness of the old pinion shim...How are you going to do that....
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Old 06-12-2018, 10:40 AM   #12
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Re: Test 4 Series Posi

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When putting it all back together, you will need to know the thickness of the old pinion shim...How are you going to do that....
A lot of measuring! I have a dial micrometer and a pinion depth kit, will be attacking that later today or tomorrow.
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Old 06-12-2018, 10:59 AM   #13
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Re: Test 4 Series Posi

Can you take pics on your measuring, I never seen that done before....thanks.
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Old 06-12-2018, 11:44 AM   #14
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Re: Test 4 Series Posi

There are actually some really good articles online to show that, better than me taking crappy cellphone pics!

Here are two from Hotrod.com that have helped me over the years:
http://www.hotrod.com/articles/gm-12...install-guide/
http://www.hotrod.com/articles/1005c..._shaft_housing

Lots of info. There was even an article in C10 Builder's Guide last month that walked thru the process. Definitely need specialized tools, and they aren't cheap for the good ones. I have the Summit one, it's an $80 setup, and it's just OK... but the good set is over $300 (!!) and I don't do this very often so can't justify the cost. If I open my shop like I plan to next year, I'll probably spring for it.

Hope that helps. I'll try to take some pics too if you need.
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Old 06-12-2018, 12:56 PM   #15
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Quote:
Originally Posted by 69SCSS View Post
There are actually some really good articles online to show that, better than me taking crappy cellphone pics!

Here are two from Hotrod.com that have helped me over the years:
http://www.hotrod.com/articles/gm-12...install-guide/
http://www.hotrod.com/articles/1005c..._shaft_housing

Lots of info. There was even an article in C10 Builder's Guide last month that walked thru the process. Definitely need specialized tools, and they aren't cheap for the good ones. I have the Summit one, it's an $80 setup, and it's just OK... but the good set is over $300 (!!) and I don't do this very often so can't justify the cost. If I open my shop like I plan to next year, I'll probably spring for it.

Hope that helps. I'll try to take some pics too if you need.
I have seen where the big pinion bearing was honed out to slip onto the pinion gear easy so you could use different shims to get the right depth into the ring gear. Once you know the correct shim than you can press the NEW big pinion bearing onto the shaft. Really no tool needed to do this but ruining a new 10 dollar bearing.
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Old 06-12-2018, 01:21 PM   #16
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Re: Test 4 Series Posi

There's an old saying "keep the pinion shim with the housing". Changing bearings, differential case (carrier to some) does not change the pinion depth to ring gear relationship. Gear sets are manufactured to known measurements too. Their replacement theoretically does not change pinion depth (unless marked + or -)

How many axles have perfect pinion depth from the factory? Not many. It certainly doesn't hurt to check it and adjust it.

edit to what Youngpup said, working on Dana axles; test bearings are essential since the shims are the side bearings on the case. (under the race on the pinion)
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Old 06-12-2018, 02:52 PM   #17
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Re: Test 4 Series Posi

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Originally Posted by Bigdav160 View Post
There's an old saying "keep the pinion shim with the housing". Changing bearings, differential case (carrier to some) does not change the pinion depth to ring gear relationship. Gear sets are manufactured to known measurements too. Their replacement theoretically does not change pinion depth (unless marked + or -)

How many axles have perfect pinion depth from the factory? Not many. It certainly doesn't hurt to check it and adjust it.

edit to what Youngpup said, working on Dana axles; test bearings are essential since the shims are the side bearings on the case. (under the race on the pinion)
I already mic'd the pieces of the old pinion shim and it's right where I would guess I should use - .027". I am going to measure anyway, but I would be surprised if the number comes out more than +/- .001. I don't want to do it twice, so I'll double check everything before I button it all up!

And yea, I'm going to hone out the other old pinion bearing I have and use it to test. Easy way to check before anything permanent like pressing on the new bearing! Now, hopefully I can get the old bearing that's stuck on there off soon
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Old 06-12-2018, 03:10 PM   #18
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Re: Test 4 Series Posi

Cut off wheel and a big chisel are your friend
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Old 07-07-2018, 12:37 PM   #19
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Re: Test 4 Series Posi

Man, I'll tell ya, they don't make rebuild kits the way they used to. All the bearings and shims have been fine, but so far I've had to swap crush sleeve (wrong part) and now the pinion nut (damaged threads). I haven't had much time to get this thing back together as summer is the busiest time of year when you work at a school, but this is really making this take forever! Had to order a pair of pinion nuts from Summit so I could get this done. I need my truck back dammit!!!

Anyone else have issues with the JEGS 12 bolt rebuild kit?
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