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Hello, I have a 96 Impala and its starting to turn into a one wheel wonder. I want to replace the posi with a Eaton Detroit Truetrac part#TT70P53041. I want to keep my stock gears. I like the grandma gears for highway use and MPGs. Is there any other parts I need to make replacement? I plan on taking the car to a shop to have the posi swapped. Thank you all.
 

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Are you replacing the factory unit because you want the Eaton, or because you think you need to?

Inaccurate suggestion - See posts below from those more knowledgeable than I
Depending on your situation, maybe consider just re-clutching/adjusting the factory posi unit rather than replacement? Less cost, less risk of things getting messed up, etc?

If you want the Eaton regardless, no problem, just wanted to present another option to consider
 

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The stock unit is an Auburn, and not rebuildable. Swapping the posi is easy...check the lash before you take it apart, and put it back with the same lash. Other than that, unless there are worn axles, you have no other changes. If you have 2.56 gears, you need a spacer to align the ring gear.
 

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If your rear end is currently quiet and the pinion seal is bone dry then I more or less agree , new limited slip , new "special" side bearings , put backlash back to what it was before.
This may require different shim combination to get the as the bearing seats and ring gear flange may not be EXACTLY the same relationship.
Make sure there is some pinion preload. There are used bearing specs.


2.56 gears , he has a 96 impala, pretty doubtful

Spacer
Lets say he did have 2.56 for sake of argument.
To put 2.56 gears on a posi made for 2.73 and up, the spacer would have to be magical.
As in space the ring gear closer to the flange.
Spacers are used to put higher series gear sets on lower series cases not the other way.
 

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Grandma gears to me are 2.56. I never had to replace 2.56 gears, but I do know they are not compatible with the higher numerical gearsets. Since he is keeping his gears, it does not matter.
 

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I had it backwards. So you have never made a mistake, and you seem to want to vengefully rub this in my face.
 

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I make mistakes all the time and if I post incorrect info , once I find out I try to make sure people know my info was wrong.
Vengeful, no
Should we not point out incorrect info?
Say I don't and someone that hangs on your words reads the post and buys a spacer and trys to put a series 3 posi in his 2.56 gear car.
Is that a better out come?
 

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Depending on your situation, maybe consider just re-clutching/adjusting the factory posi unit rather than replacement?
I'm curious what you're referring to.

Consensus seems to be that the stock posi is not rebuildable, but I also wouldn't be surprised if you figured it out, haha.
 

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Often , as many here know when the production Auburn " gives up" the cones and housing have worn to the point the cones are bottoming as well as lost preload.
Enterprising guys have clearanced the cone to housing contact points , pressed the side gears off the cones and fitted shims-spacers between them to reduce spider lash AND give preload back to the cone -housing interface.
I would call this fixing , rather than rebuilding .
The Eaton is truely rebuildable as you can buy the wear parts if they are worn to the point that shiming is not viable.
Haven't fixed an Auburn , just read about it.
Two of my diffs have them and " touch wood"
 

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I'm incorrect on this one - my apologies for any confusion.

I'm curious what you're referring to.

Consensus seems to be that the stock posi is not rebuildable, but I also wouldn't be surprised if you figured it out, haha.
Often , as many here know when the production Auburn " gives up" the cones and housing have worn to the point the cones are bottoming as well as lost preload.
Enterprising guys have clearanced the cone to housing contact points , pressed the side gears off the cones and fitted shims-spacers between them to reduce spider lash AND give preload back to the cone -housing interface.
I would call this fixing , rather than rebuilding .
The Eaton is truely rebuildable as you can buy the wear parts if they are worn to the point that shiming is not viable.
Haven't fixed an Auburn , just read about it.
Two of my diffs have them and " touch wood"
 

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To swap the posi only you will need, at minimum, a set of large journal carrier bearings/races for the Tru Trak. It wouldn't be a bad idea to just get a "Master Overhaul Kit" which comes with the following:

Master Overhaul Kit for gears and differential (includes mini install kit, large journal carrier bearings, & adjustable shims)
The kit contains:

Pinion bearings and races
Carrier bearings and races
Pinion and carrier shims
Pinion nut and washer (may not require washer)
Ring gear bolts
Marking compound and brush
Red loctite for bolts
Cover gasket
Pinion seal
2 crush sleeves
Pinion shims
Super carrier shims
Instruction booklet
 

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OP

get the "master Install Kit"....while "in theory" using the same shim stacks gets you back to where you are now relative to preload...the different part (Eaton) and associated install kit you should measure

While I do wrench on my cars, installing diff/gears I have a shop do it. I don't have the tooling nor experience as, IMHO, it is not only a learned skill...but a practiced one to.

There is also a good chance the outer axle surface is worn, and outer bearings and axle seals are needed along with new axles

Over the years I have had a few gear ratio and Eaton put in the SS. Use the same shop and watch. Among the many specific tools required, the long axle tube brushes are another tool I don't have but you really want to clean the ENTIRE inside of axle housing, just my $.02
 

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I have this exact same issue and have been looking at the options. Kinda thinking about a gear change since I dont drive long distances and more and would love the perf change.

Dare I ask what the group recommends for a full posi replacement option?
 

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Dare I ask what the group recommends for a full posi replacement option?
Dan @ Clear Image set you up with all the parts or places like Summit but not sure about Summit having reluctor gear. A forum member, Bob Shirley does make reluctor gears

IMHO a limited slip diff by Eaton. I have the 400# spring one. Get the corresponding "master install kit". Gear choice....you will get a variety of answers. For me, if you have an automatic, is 3:42 for a street/cruiser car. If it's more about 1/4mi or just city driving than 3:73. If I still had a 4L60E trans I would and did run 3:42's. The 3:73, for me, didn't give me that much more in ET than the 3:42 did at the drags and I hated the higher ROM's on Fwy.

Of course, IMHO, a T56 with 4:10's is the best...but I am partial :cool:

For anything other than the stock 3:08 gear you will also need the corresponding "reluctor" gear so your ABS is happy and a PCM re-program for whatever gear ratio you do get and whatever tire size you run so speedo is accurate. There are self programers available (Hypertech) to do this change or send your PCM to a tuner who can do it and also have "performance" parameters done for more power. It is well known the self programmers sold do very little if any HP gain
 

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Most popular combos:

Street/strip - Eaton Super Brute and 3/73.
Street/autocross or open road course or just cruising - Tru Trak and 3.42.

With the Tru Trak you are looking at $1288.20. That is for the posi, Master overhaul kit, AAM gears with ABS provision, ABS reluctor ring, axle seals & bearings and an aluminum T/A cover (not required but most get it. It has a drain plug and is suppose to stiffen the rear end). $100.00 discount included. Shipping to be determined.

Everything above except with the Eaton Super Brute instead of the Tru Trak = $1358.20 plus shipping.
 

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Gear choice . . . you will get a variety of answers.
For me, if you have an automatic, is 3.42 for a street/cruiser car.
If it's more about 1/4mi or just city driving than 3.73. If I still had a 4L60E trans I would and did run 3.42.
3.73, for me, didn't give me that much more in ET than 3.42 did at the drags and I hated the higher RpM on Fwy.
Variety of answers? It's 3.42 or 3.73.

Under 3.42, frankly, I don't understand - but I don't spend 80% of my driving time in 4th.
If not for the (possibility of) driveshaft vibes, & the fact that gasoline may never hit $2.999 a gallon again, '3.73 or 3.42?' would be a question never asked - it'd be 3.73, and that'd be the end of it.

That said, without a higher-stall RpM torque converter, the meaningful differences between 3.42 & 3.73 are worse highway MpG and the possibility of driveshaft vibes.

Pretty much the same experience as BALLSS. Had a 3.42 wagon and a 3.73 9C1-LT1 sedan.
When I had the opportunity to make my sedan a 3.42, I should have.

4.10 & up is for SERIOUS RACERS.
 

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There is no magic to assembling a rear. Cleaning is important as in any precision mechanical part. The assembly is really straight forward. The instructions are even in the FSM. If you start with a .036"-.042" shim on the pinion, and set your lash per FSM specs, you will be successful. If you use the above pinion shim numbers, and set your lash to .005"-.009", you will get a good pattern on the gears. What appears to be magic is taking the time to shim the axle carrier. You must use some math to get the right shims in place (read the FSM). Most of the tools for removing and installing parts are available as loaners from Autozone. Some can be made from available materials. There are three tools that are a must have, that you will not be able to get from Autozone, one is the dial gauge with magnetic stand for setting the gear lash, in.lb. dial gauge torque wrench to set the preload on the pinion bearings, and the yoke wrench to hold the yoke while tightening the pinion nut (available from Summit, or JEGS). You will be knocking out bearings, seals, and races, then installing new ones. You need a socket to match your pinion nut, and must install the sleeve, bearing, seal, and yoke on the pinion shaft before putting the nut on it. The only thing the book does not mention is putting some sealant on the splines for the yoke, so it does not leak. It is not magic, it is precision, and some work.
 
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