12 bolt evaluation and parts

GSDrew
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12 bolt evaluation and parts

Postby GSDrew » Mon Feb 23, 2009 2:02 pm

Hi Jim,
I picked up an A-body 12-bolt housing w/ a series 3 Eaton posi unit, a burnt/worn 3.73 Richmond gears and after-market axles. I got this set up very cheap because the seller took it all apart, lost a few pieces, lost interest and a couple years later (now) sold it to me... to get his mother off his back.
The seller bought this rear-end complete w/ new after-market axles and a newly rebuilt Eaton Posi unit and gears about 5 years ago. After 2 years and only 1,000 to 2,000 miles the rear-end started "binding-up". He took it apart and after a year without his car he went and replaced the complete rear-end. Wish I had that kind of money. The parts then cluttered his mothers garage for another year.
At any rate I now have it. A buddy of mine says the gears will need to be replaced and even though the bearing are relatively fresh Timkins they should also be changed... so I'll take his advice.
So I need:
1. A set of Richmond gears, 3.55.
2. An installation/rebuild kit w/ Timkin bearings.
3. The "Other" missing parts. I don't know enough about posi units and my buddy has never delt with a 12 bolt, so we don't know what's missing... other than the obvious.
The only parts that I know are missing are:
1. The spider gear shaft.
2. The spring assembly.
3. One of the 4 half-moon clutch ear keepers. If you know what I mean?
4. The mechanical device that tells the unit to lock or unlock.
5. A drawing that shows how to but all the parts back together.
I've attached an image of all the parts that came with it so you can tell me what else I need.
BTW... After I get this all back together I'm going to take it to a local rear-end shop to have them give it a final blessing.
Thanks for being here,
-Drew
DSCF0011.JPG

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monzaz
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Re: 12 bolt evaluation and parts

Postby monzaz » Tue Feb 24, 2009 11:11 pm

Ok Drew, here we go.

Parts missing from the piCture.
- one clutch guide (half moon metal)
- 1 pinion shaft
-1 lock washer for the retaining bolt
-1 set of 4 preload springs
-1 set of preload spring plates (2)
- make sure you have 18 clutches 9 on each side

some other parts NOT needed are the thin c shape metal spring clip...???
also the one smaller dirty looking washer between the side gear and clutches in the picture you provided. on top of all the rest of the carrier shims and clutch shims.

Rebuild kit will have all the shims bearings etc to rebuild the center section area of the housing assemble. It will not include the axle bearings and seals they are a add on kit.

There is NO mechanical device to lock and unlock the unit. This is a performance posi unit and is always on and working limited slip unit. The preload shims will be over come by the inside and out side wheel when turning left or right. when the preload is over come the clutches connected to the side gear splines will disengage or slip between the clutches with tabs that are stable in the case.

YOU WILL NEED LIMITED SLIP DIFFERENTIAL ADDITIVE FOR THIS UNIT WHEN YOU DO INSTALL THE FLUID. NO SYNTHETIC OIL EITHER.

The red indicates not needed parts
the green arrows are pointing to where these shims go.
purple circle indicates carrier shims these will be included in the rebuild kit.
Attachments
DREW POSI.JPG
J D Race

GSDrew
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Re: 12 bolt evaluation and parts

Postby GSDrew » Wed Feb 25, 2009 1:55 pm

Hi Jim,
Thanks for the feed back. You know I thought that spring clip went to a universal, just wasn't sure if it was also used in a posi. LOL. I've PM you about the replacement parts.
Thanks again,
-Drew

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monzaz
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Re: 12 bolt evaluation and parts

Postby monzaz » Wed Feb 25, 2009 10:45 pm

Yah now that I look at it closer you are correct it is a inside u-joint spring clip. Still do not know what the other washer red x out is...LOL. Jim
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GSDrew
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Re: 12 bolt evaluation and parts

Postby GSDrew » Thu Feb 26, 2009 2:48 pm

Hey Jim,
I hope you haven't heard this before... "The check's in the mail".
Actually it's a PMO.
Thanks for your help.
-Drew

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monzaz
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Re: 12 bolt evaluation and parts

Postby monzaz » Thu Feb 26, 2009 3:42 pm

Thanks will keep an eye open for it. Take care, Jim
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txgdwrench
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Re: 12 bolt evaluation and parts

Postby txgdwrench » Wed Mar 31, 2010 11:50 am

Tim,

I have a Eaton POSI unit EDB-32640.

I am in the process of rebuilding my carrier with new 800 lb springs (29591-00S) and a set of 18 clutch disks (29403-00S).

When I pulled my carrier apart there were two carrier shims on each side in-between the last clutch disk and the carrier. Is this correct or should one be on the gear side and one on the carrier side?

What is the correct setup?

gear/clutch/clutch shim/clutch/clutch shim/clutch/clutch shim/clutch/clutch shim/clutch/(2) carrier shims? Current setup.

gear/carrier shims/clutch/clutch shim/clutch/clutch shim/clutch/clutch shim/clutch/clutch shim/clutch/carrier shim?

gear/clutch/clutch shim/clutch/clutch shim/clutch/clutch shim/clutch/clutch shim/clutch/carrier shim?

I noticed above you stated DO NOT USE SYNTHETIC OIL. I am planning on running AMS Oil Severe gear 75W-140. This is synthetic and the AMS Oil website states that this is good for limited slip applications and does not need additive?

Thanks,

Mark

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monzaz
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Re: 12 bolt evaluation and parts

Postby monzaz » Wed Mar 31, 2010 7:54 pm

Ok, PArt number on the unit I am not familiar with... CAn you post pictures? What type of car / truck is this for?

Shimming will always depend on keeping the side gear engagement equal to the smaller spider pinion gears that ride on the cross shaft (pinion shaft). USUALLY the shimming is equal on both sides and between .010 -.040 FOR 12 bolt chevy type rears...BUT again will depend on the thickness of the clutches and wear on the case etc.

800lbs. springs. Is there a reason why you think you need 800# preload springs? What will be your main purpose of the car/ truck? If you are at all street bound you will eat the clutches up in that posi unit quick with tall that preload. 400# should be sufficient for all applications street strip .

I hope you have a great spring compressor for those 800# springs as we even have truoble with those stinkers when customers ask for them.

TAlk soon. Jim
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txgdwrench
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Re: 12 bolt evaluation and parts

Postby txgdwrench » Wed Mar 31, 2010 8:53 pm

Jim,

It is Eaton posi unit for a Chevy truck 12 bolt. It is going in a 85 1/2 ton SWB chevy.

It is an old part number, the unit was in good shape but I lost a preload spring so I decided to rebuilt it. It will be for street and strip applications. I went with the 800# due to having issues in the past with having the unit unlock during burnouts with slicks on at the track.

I attached the only picture I have of it.

Thanks,

Mark
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DSC00549 Small.JPG

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monzaz
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Re: 12 bolt evaluation and parts

Postby monzaz » Sun Apr 04, 2010 10:37 am

Sounds more like your clutch pack shimming is wrong. To tell everyone the truth the preload springs are NOT needed for the posi to work. The preload springs are really there so the clutches have a smooth transition and will help the clutches extend usefully life when getting worn.

At TOM's differentials he showed us how to set up posi units with out preload springs at all and they worked great. :)

Expect to eat clutches up very quickly with the 800# spring pressure...

Releasing tires upon burn out- Make sure you have your tires go through the water box before doing a burn out with slicks and posi unit. Once the tires are spinning well and you see smoke your done...NO need to keep burning as the smoke indicates tires are at optimal temp...unless your going for the cool factor...lol. :) If you do not have enough water for the tires (slicks) to break free easily you need more water or you need to start closer to the water box area. This will ease the pain on your posi at the track...on burn outs. Good luck

Good luck with the diff.
J D Race


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