# Rear axle codes



## Pontiacpurebrred (Jun 22, 2011)

Ok as some of you may or may not know I have a 69 Custom S, it's been through a few lives prior to my acquiring it. I decided to check the the rear axle today for the codes to check and see what I had back there.

Near as I can tell from the VIN decoding she came with a V8 (one of the less than 100,000 units V8's - if that means anything)

It had a non original 389 and TH 400 when I got it so I don't expect it to be original but this is what I found.

The only codes on the front of the passenger side of the axle are 
P2 WC in that order.
I can't find a date stamp, nothing before the P2 and nothing after the WC. 

Am I looking in the wrong spot?

It's a 10 bolt differential and it has drums. 
I did not find the Safe T Track tag.

All I can find looking for the WC code that makes sense is 1969	Tempest	2.78	39/14 WC	XC
Any help would be great.


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## 68greengoat (Sep 15, 2005)

Check by the cover. It should be cast not stamped. If it was a safe t track the code would have started with an x, y or z for '68 - '72. y or z for '65 - '67.


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## Pontiacpurebrred (Jun 22, 2011)

only thing I can find CAST on the case is 9799100 with F100 above it.
That's on the rear of the passengers side of differential.


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## Tambo (Aug 15, 2011)

Check rear axle numbers here ... GTO Axle Identification


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## 68greengoat (Sep 15, 2005)

Pontiacpurebrred said:


> only thing I can find CAST on the case is 9799100 with F100 above it.
> That's on the rear of the passengers side of differential.


The F100 should be the date code - June 10, 1970

I've read where all 10 bolt 1970 GTO/Lemans had that axle code, 9799100.

At any rate, it's a '70 rearend and still a WC 2.78(providing the gears haven't been changed). Real nice highway gear especially with todays gas prices... That's what I have except a '71. The 3.55 safe t track is going to have to wait....


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## Pontiacpurebrred (Jun 22, 2011)

Well alrighty then. I have a 1970 non-limited slip highway gear rear end. 
(I did the old school test, spun one wheel and the other wheel goes the opposite direction) 

Which I do not want. (shocking right?) (It's drum breaks too) 

The gears aren't bad I suppose (like you said gas prices right?) 

But I gotta have both wheels locked down. What are my options on either making this a posi or finding a replacement?
I know any 68-72 GTO, LeMans, Tempest limited slip will work, anything else out there that I can find at a junk yard or on CL that will go with minor to no modification? 
Thanks in advance.


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## 68greengoat (Sep 15, 2005)

LOL, I have drums all the way around too...

If you want to stick with the same gears, just swap out the carrier to a limited slip like this:

Auburn Gear 5420114 Auburn Gear Differentials


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## Pontiacpurebrred (Jun 22, 2011)

68greengoat said:


> LOL, I have drums all the way around too...
> 
> If you want to stick with the same gears, just swap out the carrier to a limited slip like this:
> 
> Auburn Gear 5420114 Auburn Gear Differentials


I at least have discs up front, and power all around. I looked at those, the Auburn gears, wasn't sure how it would work and if I am capable of installing such a thing. I will look into it further and also may look around for a replacement.


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## 68greengoat (Sep 15, 2005)

Power, what's that? For me it's my leg and arms. Manual everything, power nothing... Power................. someday.....


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## Pontiacpurebrred (Jun 22, 2011)

I got SUPER lucky with Marilyn, she came with power breaks (discs in front) tilt column, power antennae, remote mirror, no rust in the trunk or floor boards. Someday she will be back together and hopefully with 4 wheel discs, upgraded suspension and POSI.
lol

Thanks for all the info.


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## 68GTO4004Spd (Jun 19, 2008)

You can't just bolt in a carrier unless you know how to set up a rear end (you have to put paint on the gear teeth and adjust the lash and shim and blah blah blah). When I was looking into a carrier swap, they estimated $1000 to replace all the bearings, put in an Eaton posi and change the gears to a different ratio. That's labor only. I personally would prefer the Eaton over the Auburn unit because the Auburn has cone clutches that can't be rebuilt and the Eaton has disc clutches that can be rebuilt, and they cost about the same.


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## caralho (Apr 10, 2016)

i have a 1972 gto which originally had an automatic tranny. it was immediately changed to a 4 speed. i took out the 10 bolt posi 2.78 gear rear end and still have it in the box-virtually unused with all bearings installed . [email protected]. rear end has a gm 70 zd code. i am more than willing to sell it as i am keeping the 4 speed.


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