Help identifying posi differential unit

[Gerry P.]

I have a lead on someone selling a 3:36 posi unit and need help identifying it. The numbers the potential seller gave me were for the pinon gear which is 3819186 and the carrier assembly which is C-32324. He said it is made for 18 spline axles. All the seller knows about the unit is that he was told it may have come out of an early corvette. Any help on identifying the unit would be appreciated.
Thanks
Gerry Phillips

[Joe L.]

Re: Help identifying posi differential unit

I have a lead on someone selling a 3:36 posi unit and need help identifying it. The numbers the potential seller gave me were for the pinon gear which is 3819186 and the carrier assembly which is C-32324. He said it is made for 18 spline axles. All the seller knows about the unit is that he was told it may have come out of an early corvette. Any help on identifying the unit would be appreciated.
Thanks
Gerry Phillips

Gerry----


Gear GM #3819186 was used exclusively for 1963-64 Corvettes with 3.36:1 axle ratio. So, I'd say the chances are excellent that this is the origin of the unit in question.

[Gary R.]

Re: Help identifying posi differential unit

I'm sure Joe has the numbers down perfect. If indeed that is an original 63-64 posi case you're better served not using it. They were very weak and many haven been replaced by now. The parts to rebuild them are long gone as well. The first design Eaton is also not the best choice nor are the current new loaded Eatons. Both have issues from cracking to using cheap parts. A 69-79 Eaton posi case would be the best choice to build and also better then the Auburn cone type units.
Once installed in the housing there is no way of knowing what's inside.

[Gerry P.]

Re: Help identifying posi differential unit

Thanks Joe & Gary. If the parts are for a 63 or 64, they won't work in my '57 so I am not interested. But as a follow on question, the guy wants to sell them for $75. Now this is not the full 3rd member assembly but just the pinon & ring gears, and posi parts/assembly. This seems like a good price and am wondering what they are really worth.

[Gary R.]

Re: Help identifying posi differential unit

I wouldn't buy them,regardless. The R&P use a small sleeve, require the correct coarse spline yoke,and who know what the pattern will look like. The posi cases were plain junk for a vette.

[Gerry P.]

Re: Help identifying posi differential unit

Thanks Gary, I appreciate your feedback.

[Tom P.]

Re: Help identifying posi differential unit

Gerry,
ANY 57-62 Vette and ANY 57-64 pass car posi rear is a 100% bolt-in for your car.
There are 2 versions of this style early posi rear. Early-57/59 and late-60/64(pass car). The actual posi unit itself is totally interchangeable into any case, but the 60-64 unit is a more desireable choice.
If you just HAVE TO HAVE A FACTORY posi unit in your rear, fine. BUUUUUUUUUUUT, otherwise, I would strongly encourage you to consider buying a BRAND NEW Eaton posi unit to install in your rear. As mentioned, once installed into the rear axle housing, there is NO WAY for anyone to tell what is inside. The old factory posi units (made for GM by DANA) are just that, old, possibly heavily stressed, may have cracks and virtually no parts are available for them any more except clutches------------------and the currently available clutch pack from DANA does not contain the correct clutches!
If your 57 rear is a NON-posi, and you desire to convert it to posi, it is quite simple. BUUUUUUUUUT, it will require a slight modification to the non-posi case which is SUPER SIMPLE to do at home on the work bench. If you need more details or pictures regarding this modification, I can post them. AND, it does not matter if you are converting a non-posi rear with a factory or Eaton posi unit, it is still necessary to perform the modification.
I've done this many times for customers through the years.

[Gary R.]

Re: Help identifying posi differential unit

Hi Tom,
Do the C1 loaded Eaton use the fiber clutches in them as well? If so those really don't hold up well, plus on the 63-79 units they cut out a set of plates/disc per side to use those huge yellow springs. I don't work on the pre 63 diff's so I'm not familar with them enough to know.
Thanks
Gary

[Tom P.]

Re: Help identifying posi differential unit

Gary,
I don't know what the clutch material on the new Eaton posi plates for the 55-64 style rears is made of. Because that particular posi unit is a new item to their product line, I've not yet had one apart. Obviously, there was enough of a demand for this particular posi application that Eaton began manufacturing them just a few short years ago (3-4?).
So all of my experience with them so far has been installing them, rather than servicing any of them. Therefore, I've not yet had the clutches removed from them to inspect the plates for wear or any other reasons.
Eaton has been around many years and has made posi units for GM cars for a LONG time. Consequently, for the most part, Eaton posi units in earlier cars (Chevelles, Novas, GTOs, Camaros, etc, etc) have been known for their durability. And so far, I have neither seen, heard or read about problems or dissatisfaction with the new Eaton for these early Chevy rears. So, so far, I'm pleased with them.
That's the best personal experience I can provide.

[Gary R.]

Re: Help identifying posi differential unit

Thanks Tom,
Sorry if I pulled this thread in a different direction. I agree on the Eaton product line but I'm limited to the corvettes from 63-79. There was a design improvement from the 65-68 to the 6-79 design. I'd say 50% of the 65-68's I see are cracked, where as few of the 69-79 are. The clutches changed as well during this run but the quaility went down from 71-79 on them. I see many pushing the fiber coated clutches but I've had them rub off in my hand and know of others that failed in HD usage.

[Gerry P.]

Re: Help identifying posi differential unit

Thanks Tom for your comments, always appreciated. To clairfy my objective, I'm not really looking for a posi unit for my '57. In fact the 3rd member that's is in the car now is either a '61 or '62 3:08 posi. Since this differential is not correct for my car, I just want 3rd member that is correct for the car, posi or non-posi (since I'm not racing or driving in rain or snow). In fact, I'm not sure if a posi was even available for an Oct '56 build corvette - you may know the answer to that.

In any event, I've found a date correct '57 diff housing but it has no gears so am keeping my eyes open for parts to complete its build up. I'm hoping to find an old set for not too many $$. Once I can get the '57 diff complete, I will probably try to sell the later year posi that I'm currently running.
Gerry Phillips

[Tom P.]

Re: Help identifying posi differential unit

Gerry,
Posi WAS NOT available until about Dec 56 (either in Vettes or Pass cars).
If you have located a correct dated case, the rest is EASY, EASY, EASY!!!!!!!!!!
You simply need a good ring and pinion gear set (use ANY 57-64 R&P set) of your choice of ratio------------------ONCE INSTALLED, IT CANNOT BE SEEN!!!!! I have a BUNCH of non-posi differentials in good condition (I've saved them, God only knows why, from posi conversions), and I'll GIVE you one (I have BOTH 3 and 4-series), you buy the shipping (or drive to my house and pick it up).