# Help with rear diff.



## Goat noob (Apr 16, 2021)

Hey all,

I recently noticed I am leaking diff fluid from my 68 rear end. I know the easy and cheap fix would be to change fluid and gasket. I’d like to upgrade my diff. My axel tube is stamped “WG” Google suggest that’s a 3.36 posi? The car is a one wheel peel and can’t move out of its own way. Did all goats come with positraction? If so, my diff is not original. Can I assume this is a 8.2 BOP rear so I’ll have to stick with a 8.2 housing? Let me know what you guys think. Everyone has been very helpful on this forum and I appreciate it


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## PontiacJim (Dec 29, 2012)

Goat noob said:


> Hey all,
> 
> I recently noticed I am leaking diff fluid from my 68 rear end. I know the easy and cheap fix would be to change fluid and gasket. I’d like to upgrade my diff. My axel tube is stamped “WG” Google suggest that’s a 3.36 posi? The car is a one wheel peel and can’t move out of its own way. Did all goats come with positraction? If so, my diff is not original. Can I assume this is a 8.2 BOP rear so I’ll have to stick with a 8.2 housing? Let me know what you guys think. Everyone has been very helpful on this forum and I appreciate it
> View attachment 143085


Most GTO's did not have posi - it was an option. You can add a posi unit if you know how to do this, otherwise a shop can do it. The PHS documents for your car will tell you what gear ratio the car was born with. 3.36 is a favored gear for all around driving. If you go 3.55, and up, you will lose highway driving comfort and the engine will be run at higher RPM's. The casting codes/dates will also confirm the rear end.

Stock tire height was 26". If you use a taller tire, like 28", you will effectively drop the gear ratio to something like 3.23's. This can cause the car to seem a little more sluggish.

Acceleration is a product of HP/TQ. If you have a good engine, 3.36's should move the car just fine. A single legger will spin the tire. You can go a little wider on the tire. There really is no BOP rear end, although parts can sometimes interchange. Buick and Olds did develop their own rear ends, but used Pontiac rear ends in the earlier years. So not a 100% accurate label.


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## Goat noob (Apr 16, 2021)

I have a ton of documentation for the car, I’ll have to find it. I’ve moved more than a few times since I purchased the car. My tires are closer to 28” so that makes sense and motor is a 557 code 👎. If I can’t locate info on the diff in my documents can I pull the rear and physically ID what kind of rear it is?


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## armyadarkness (Dec 7, 2020)

My car came without a posi. I just installed one and it took less than 2 hours to do it. Plus, it's a great opportunity to inspect and replace all of the 50-year-old bearings and seals. Based on your picture, that's what would be considered BOP by Auburn or Eaton, when buying the carrier.

If you're keeping the same gear ratio, and your pinion bearing isnt making any noise, then you can swap your old gears onto the new carrier, and if anything is required at all, shim side to side.


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## Goat noob (Apr 16, 2021)

So my rear is stamped as a 3.36 and I was originally planning on buying an Eaton posi unit but I might just replace the gasket and fluid to stop the leak. I’m sure a posi unit would be more enjoyable to drive but it doesn’t seem worth the coin to swap the units at this point if the gears will remain the same.


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## coyote595 (Dec 4, 2019)

Make sure your pinion seal isn't leaking and blowing back and dripping off the cover gasket area.


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## Goat noob (Apr 16, 2021)

coyote595 said:


> Make sure your pinion seal isn't leaking and blowing back and dripping off the cover gasket area.


The bottom of the pumpkin is dry. The gas tank has black fluid on it so I suspect it’s coming from the top of the pumpkin… you can see it in the pic I posted above.


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## BLK69JUDGE (Jun 10, 2010)

your tank is leaking
that black goo is gas and undercoat

drop the tank ,,,, bad rubber fuel line is where I would put my money
or
the front of the middle seam rotted out,,,, 

a differential leak would end up dripping off the bottom of the cover /case


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## Goat noob (Apr 16, 2021)

BLK69JUDGE said:


> your tank is leaking
> that black goo is gas and undercoat
> 
> drop the tank ,,,, bad rubber fuel line is where I would put my money


That’s a relief! I bought a fuel sending unit, my gas gauge stopped working last month.


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## Goat noob (Apr 16, 2021)

Goat noob said:


> That’s a relief! I bought a fuel sending unit, my gas gauge stopped working last month.


I wonder is the black goo all over my garage floor is just undercoat and gas and not diff fluid at all…. It doesn’t really smell like gas.


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## armyadarkness (Dec 7, 2020)

Goat noob said:


> So my rear is stamped as a 3.36 and I was originally planning on buying an Eaton posi unit but I might just replace the gasket and fluid to stop the leak. I’m sure a posi unit would be more enjoyable to drive but it doesn’t seem worth the coin to swap the units at this point if the gears will remain the same.


As Jim said, if the engine is right, then 3:36 is quite a bit of fun. If you don't like the 3:36, then by all means, swap the gears, too.


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## Goat noob (Apr 16, 2021)

armyadarkness said:


> As Jim said, if the engine is right, then 3:36 is quite a bit of fun. If you don't like the 3:36, then by all means, swap the gears, too.


The engine is very weak, it’s not the stock motor. I’m currently looking for a late 60’s early 70’s Pontiac 400 to build and swap this tired 400.


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## armyadarkness (Dec 7, 2020)

Goat noob said:


> The engine is very weak, it’s not the stock motor. I’m currently looking for a late 60’s early 70’s Pontiac 400 to build and swap this tired 400.


The engine is very weak... Meaning old and tired or healthy, but low performance? If it's a healthy, low performance engine, then drop to a better gear... a 305 Chevy is a ton of fun with 3:73's. But if the engine is tired, then (with a heavy foot) low gears will expedite its demise.


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## Goat noob (Apr 16, 2021)

it’s never left me stranded but I did a compression test and found out I have low compression in cylinder #6. And it’s a 500557 stamped block so it’s not a great candidate for a performance build. I had a 3.73 in my Chevy 350 that was a ton of fun but I was having too much fun and cooked it. Once I find a sturdy engine block I plan to putz around with the car until the new 400 is ready to go.


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