69 rear end research - Pontiac GTO Forum
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post #1 of 11 (permalink) Old 01-01-2018, 06:05 PM Thread Starter
 
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69 rear end research

Here is what I want to do:
1. I want to "restore" my car to the "original" posi setup. I don't necessarily need/want to find an original OE posi unit (would need rebuilt causing more delays and cost) but it did come Safe-T-Trac posi so I want to get that option back.

Here is what I've found so far:
1. I don't want/shouldn't use a locker kit - poor turning performance/ease, mainly for racing which I won't be doing - much of it anyway, I may take her to the track for fun runs.
2. I probably want and Eaton Posi unit versus and Auburn (two main types I've found).

Here is what I know:
1. I own a 69 GTO with an open diff.
2. Gears are 3.23 - which my car came with originally(as well as a TH400). I would stay with 3.23 or go to 3.55 unless I hear some convincing arguments to "upgrade". So far I'm happy with driveability and the highway RPMs of my current setup.
3. Housing is a 8.2" ten bolt.
4. All bearings/seals were replaced (diff rebuilt) two summers ago.
5. installation is not tough but will probably have a pro do it for the warranty - which I've used several times on the rebuilt rear end and transmission.
6. I recently had my engine rebuilt with a mild cam upgrade and roller lifters as the only upgrades outside of .30 over bore, better pistons/rods etc. I will have slightly more than the stock OE ~360 HP when new.

Here is what I don't know:
1. What rear end/axle housing I have, I know it's NOT from a GTO but it is BOP?
See pics below. If someone can help with identifying what I have I would be greatly appreciative.
2. What posi unit I CAN use in the current rear end/axel I have - assuming I have the correct axles for a Pontiac. I am on the look out for an original 69 GTO rear end but if I can get a posi unit which would fit both it would be a bonus so I can do this once.

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A couple more pics below...

*67K miles... Under Construction* :)
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post #2 of 11 (permalink) Old 01-01-2018, 06:06 PM Thread Starter
 
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Thanks in advance.

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*67K miles... Under Construction* :)
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post #3 of 11 (permalink) Old 01-01-2018, 07:20 PM
 
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Gray iron Pontiac 8.2 10 bolt housing cast Oct 1st, 68. Does it date your '69's build?

The gray iron Pontiac 8.2 housings are fine for lower torque builds with automatic transmissions. As a longtime differential builder, I've picked through the pieces of dozens of gray iron 8.2's that were "upgraded" to lower ratio gears & destroyed due to lack of pinion support. I personally will not go through & add a posi unit for such gray iron 8.2's for higher torque builds. For a putt-a-round cruiser, ones looking $700-800 to propperly add a mid ratio Pontiac 8.2 carrier in place of what was a single track 8.2 Pontiac carrier. Last, i never recommend sealed axle bearing axle Pontiac 8.2's, Buick 8.2's, or '67-69 Type "0" Olds 10 bolts for A-body's that are seeing considerable handling mods, the archaic sealed bearing axles were not designed for strong side loading forces with wide tire/wheel combinations.
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post #4 of 11 (permalink) Old 01-01-2018, 08:08 PM Thread Starter
 
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Thanks, I was hoping you would reply Pinion Head... yes, I have an early '69 build with all it's features (I.E. 4" water pump) etc.

So if I read this right, taking into account I've not made the mods you mentioned (significantly higher torque or handling mods) I should be okay using my current housing with a new 3.23 or 3.55 posi?

With your experience is there a better more reliable posi than most I.E. Auburn, Eaton, Yukon etc? My planned application is a cruiser with occasional hard runs on the street and highway and making a few fun run nights in the summer.

Thanks again for replying.

Quote:
Originally Posted by Pinion head View Post
Gray iron Pontiac 8.2 10 bolt housing cast Oct 1st, 68. Does it date your '69's build?

The gray iron Pontiac 8.2 housings are fine for lower torque builds with automatic transmissions. As a longtime differential builder, I've picked through the pieces of dozens of gray iron 8.2's that were "upgraded" to lower ratio gears & destroyed due to lack of pinion support. I personally will not go through & add a posi unit for such gray iron 8.2's for higher torque builds. For a putt-a-round cruiser, ones looking $700-800 to propperly add a mid ratio Pontiac 8.2 carrier in place of what was a single track 8.2 Pontiac carrier. Last, i never recommend sealed axle bearing axle Pontiac 8.2's, Buick 8.2's, or '67-69 Type "0" Olds 10 bolts for A-body's that are seeing considerable handling mods, the archaic sealed bearing axles were not designed for strong side loading forces with wide tire/wheel combinations.

*67K miles... Under Construction* :)
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post #5 of 11 (permalink) Old 01-01-2018, 08:10 PM Thread Starter
 
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PS. and is the cost you mentioned $7-800 include the posi unit and labor?

*67K miles... Under Construction* :)
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post #6 of 11 (permalink) Old 01-01-2018, 08:27 PM Thread Starter
 
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I found this at Wallace Racing.com

This helps... now I know what you mean by lower gear ratios, makes more torque.

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*67K miles... Under Construction* :)
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post #7 of 11 (permalink) Old 01-02-2018, 11:01 AM
 
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Interesting stuff, Dan. PHS says I have a 2.93 peg-leg but there are indications that like the engine and TH400, the rear end came out of the Safe-T-Trac donor "69 Grand Prix. Once I recover from lumbar surgery, I'll go under and investigate more. In the interim, I'll follow your thread, Thanks.
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post #8 of 11 (permalink) Old 01-02-2018, 06:21 PM Thread Starter
 
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It certainly is... As with other stuff I've never done this should be a learning experience. Here is the site I found the data on.

Optimum Rear Gear

Quote:
Originally Posted by 1968gto421 View Post
Interesting stuff, Dan. PHS says I have a 2.93 peg-leg but there are indications that like the engine and TH400, the rear end came out of the Safe-T-Trac donor "69 Grand Prix. Once I recover from lumbar surgery, I'll go under and investigate more. In the interim, I'll follow your thread, Thanks.
At some point my car had the transmission replaced with a 69 GP model and I think the rear end is as well... I look forward to smokin both tires at one time!

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post #9 of 11 (permalink) Old 01-02-2018, 09:39 PM
 
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There is only one aftermarket posi carrier avail today for the mid ratio Pontiac 8.2 gearsets. It's an Auburn "performance series" cone type. Personally, I don't like the Auburn cone type posi's, like gray iron 8.2 rears, will only build with them when put on the spot to do so.

The '69 & 70 Pontiac 8.2 Gray iron 10 bolts used in Grand Prixs have a formed flat spot on top of each axle tube. This is spot is aprox 5" long & begins several inches inboard of each backing plate on the housing. There are two different 97xxxx casting number gray iron housing Pontiac 8.2 rears that were used in '69 GP models. There also was a nodular hsg used in lowest ratio HD STT rears. I have yet to find a tapered axle bearing Pontiac 8.2 rear original to any '69 Pontiac A-body or GP. In the late 90's I hauled & eventually stripped down to a bare shell an 08A body built Arlington TX assembled very late production super solid '69 LeMans. Auto AC car, even being super late built, the rear was still a sealed axle bearing style 8.2 Pontiac rear, not the tapered axle bearing 8.2 Pontiac rear used just a few weeks later in '70 model GTO's, LeMans, etc.

In the '69 Firebird line, the tapered axle bearing housings definitely were introduced & used in later built '69 Firebirds. All 1969 Firebird gray iron 8.2 rears also had the flat spots die formed into the top of the axle tubes / shared same axle tubes as the Pontiac 8.2 rears in '69 & inat least '70 model GP's Besides having core rears & bare hsgs for the above, have a sealed up '71 GP partscar with it's original 8.2 Ponttiac rear in it, need to ck its hsg tubes for the flat spots.

On the '69 rear, Dan I can ck the center housing casting numbers on the '69 GP rears I have. I've only kept them as they are clean hsgs, with three of them being coded as 3.23 Safe-T-Tracks. One is out of a '69 428 HO GP I came across & hauled in the mid 90's. Love to be able to get to restoring the GP, unfortunately, it's just not a good candidate to dump funds into.
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post #10 of 11 (permalink) Old 01-03-2018, 12:55 PM Thread Starter
 
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I assume this is the "flat spot" to which you are referring... I found this out when I installed the new brake lines. That's when I figured out the car was not all original as I was told. These are GTO lines on the GP housing.

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Now to find a GTO rear end...

PS. Thanks for the additional information.

*67K miles... Under Construction* :)

Last edited by dan woodland; 01-03-2018 at 01:35 PM.
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