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Discussion Starter · #1 ·
Ordered a 9.3" posi from www.jdrace.com for the 57 Pontiac rear end I plan to put in my utility sedan. The service and delivery time were great.

The housing has been narrowed 1" and has big bearing Ford ends so that I can run cheaper/more common Ford brakes. I have Dutchman 31 spline axles and explorer rear discs to complete the rear end.

USA Made Case


 

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Finally, a new 9.3 Posi

Please let us know how everything works out with this. I saw the release of this differential a few months ago, and posted on it earlier:

http://www.trifive.com/forums/showthread.php?t=107851&page=2

I have a couple of 9.3 axles, and would like to use one on a future build, with the only thing slowing most people down is the availability of a Positraction for street driving. Did you pay about $800 even for this diff? Thanks!

Driver.
 

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Discussion Starter · #3 · (Edited)
It was your thread that told me about JD Race. I paid +/- $836 shipped. It came with bearings and races. I probably won't have it in the car until this Summer, but I will post updates.

I saw a local 3.42 31 spline posi pumpkin for sale on Craigslist. The ad didn't have a number, so I emailed him twice with no response. The following Sunday, I saw the pumpkin and some other parts he had for sale, but the seller wasn't at his spot at the Long Beach Swap Meet. I went to the restroom and when I came back, someone else was buying it...

I didn't want to pay what the rear ends were going for on ebay, so I thought I would give JD Race a try. I'm planning to set the pumpkin up myself. It will be my first time to set a ring and pinion.
 

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I know Brad of http://fabcraftmetalworks.com/ and he is the guy that has really brought the 9.3 differential back to life.

I built a Pontiac/Olds 9.3 for a local guy's '55 using Brad's parts for the build. Brad owns the rights to all the new R&P being made for the 9.3. The gears are actually made by Richmond for Brad and Richmond cannot sell them. Anyone that wants new 9.3 gears must buy them from Brad.

Check out the coast pattern picture on the left and the drive pattern picture on the right that I got. These gears setup nice, quick and run quiet.
 

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Is this a converted OEM differential??

A strange thought just came to mind on the JD Race diff: Is this a converted OEM differential for another application? Knowing how expensive it is to get custom parts cast and machined, I have often wondered if there was another common differential that is close enough to the 9.3 to just modify/machine it a little bit to adapt it to the 9.3. Here is what I am seeing with the JD part that makes me wonder:
1. They add a tack welded ring gear register ring, indicating that the original ring gear register was not the correct diameter for the 9.3.
2. The ring gear flange is drilled with two bolt patterns, meaning that one was added later.
3. They sell it "Complete with bearings" which makes me wonder if they are using a special conversion bearing, because the stock bearings will not fit?
4. If that casting number, "11 09 10" showing in the last photo is a date code, this casting is almost 4 years old, way older than something that was just developed.

Does anyone else recognize this diff as an OEM part off of something else?

Driver.
 

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This is definitely a converted differential

OK, after looking this over more, I am 100% convinced that this is a modern differential for an existing application that has been modified by machining it for the 9.3 axle. In the attached photo, you can see where the flange side differential bearing appears to be deeper in the case than on the non flange side, leaving a "stub" of the bearing shoulder sticking out. The bearing shoulder is always nearly flush with the end of the installed bearing on any differential that I have ever had apart.

You can also see where they had to machine the flange reinforcing ribs away to drill the wider bolt pattern for the 9.3 ring gear. An Engineer would never design reinforcing ribs into the casting, then specify that most of the rib be machined away in the manufacturing process.

Look at the second attached photo to see what would be typical of another Eaton style posi case that has the ribs carried to the edge of the flange. This is a proper design for transferring the bending load from the edge of the flange, to the center of the differential case, to keep the ring gear flange from fracturing under load. I am expecting that the JD case originally had ribs like this all the way to the edge.

I am not bashing on the JD Race product in any way. I am just recognizing that they have discovered another Eaton type posi unit that was close enough to modify, and I would like to know which axle it was originally produced for. If it is a modern axle that is really common, it may be possible to pick up an inexpensive used one and perform the machining operations on it to make it fit. None of the modifications are exotic.

More compelling is the thought of finding out what the differential is, and contacting the manufacturer to see if a run of partially machined (or unmachined) castings could be obtained, so they could be finished properly to the 9.3 dimensions. It would be great to not have to compromise the ribs on that ring gear flange, and it would be even better if there was enough "meat" at the center to not have to add the register ring for the I.D. of the ring gear.

Wes: Are there any other casting numbers on this case to help identify it?

Driver.
 

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Right on about the bearing spacer.

It may be a 9 1/4 Mopar truck posi. There seems to be a spacer under the right side bearing. The alternate holes for the ring gear are 7/16 rather than the 3/8 holes for the pontiac ring gear. If I didn't have powerlock posis already I would consider this conversion.
Looks like I was typing while you posted. Yes, Tom right on about the bearing spacer. After closer examination of the photo, (attached) you can see where the bearing shoulder is recessed inside the bearing from the addition of the spacer.

This case wants less ring gear flange offset as originally machined. Boy, I wonder if an unmachined casting could be obtained, if there is enough meat in the original to offset that ring gear flange enough to get rid of the funny bearing placement? This is probably a permanent mold type casting, which is not easily modified. If we could just get a little less offset in the raw casting, all the finish machining could be right on the money...

Driver.
 

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Discussion Starter · #10 ·
It looks like they are trying to protect their source.




Good catch on the machined ribs.

I'm not sure if I'm going to go for a day 2 type build , or a turbo'd LS. If I swap the stroked 327 from my 62, the car will probably run mid to high 11s. However, if I swap my LS2 and turbo it, I will be in the low-mid 10 sec range. I'm hoping the Pontiac rear will live behind either combination.
 

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Fabcraft posi

So fabcraft finally came out with their posi? When I spoke with Brad last fall about it, he was on hold indefinitely. Do you have a link to data and pricing on the new fabcraft unit?

Driver.
 

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So fabcraft finally came out with their posi? When I spoke with Brad last fall about it, he was on hold indefinitely. Do you have a link to data and pricing on the new fabcraft unit?

Driver.
I will call Brad at Fabcraft today and talk to him, I bought a new posi from him about two years ago for the '55 Chevy shop car.

I don't remember pricing as I have an account with him but, I think street pricing was around $800? I will get the scoop later today.....
 

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I don't see a big deal to customizing a case intended for another application - unless that causes problems with setup.

The posi unit fills a hole that many wanted to see filled. It still wouldn't motivate me to use a Pontiac/Olds axle, but I know that there are quite a few that do.
 

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It still wouldn't motivate me to use a Pontiac/Olds axle, but I know that there are quite a few that do.
My business partner had to have this differential for his '55 shop car but, he had no idea how much it cost to rebuild the center section. The new posi units and R&P gears are 1-1/2 to 2 times more than other units.

If memory serves me correctly, I think Mike had over 3k in parts for the rebuild, which included new axles and a yoke.

Luckily, he had the differential already and I didn't charge him labor!
 

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Discussion Starter · #19 ·
I paid $125 for a complete '57 Pontiac rear I found on Craigslist in WA. I paid $1150 to have the housing narrowed 1", Ford big bearing ends, 31 spline dutchman axles, and disc brakes. If I successfully install the posi myself, I'll have about $2200 in it. There were easier and cheaper options, but I wanted to build my car the way I used to hear my uncles talk about the good old days. Nostalgia isn't cheap.

JD Race was responsive to my questions and shipped quickly. I've also been happy with my dealings with Fabcraft. If this rear end works as intended, I will probably do one for my 62.

I will post updates on the rear as I go.
 

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I stand corrected, the posi unit that my business partner bought from Brad was a shot peened original posi that was rebuilt with all new internals.

I swear that thing looked like new!
 
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