Adding Posi

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69hurstolds

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It’s not an improvement per se. It’s certainly a good rear but a bit overkill if you’re just wanting to upgrade your stock rear to posi, IMO. A stock 8.5 will hold up to some abuse. Spending more money than you have to is optional. If you’re running a stock 307 or even a stock 455, the 8.5 will hold up without issue and last the life of the car, properly maintained. It’s already been 38 years. For a few hundred bucks and a little luck with your gear set condition, you can make it last another 38 years with a freshen up.
 
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64nailhead

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Ok, I’ll bite: why would the s60 be an improvement?
Dana S60 vs GM 8.5 - the Dana will handle anther 300 ft/lbs without issue.

Your rear can be built to a very respectable level. It comes down to how much do you want to spend? You can convert it to a 30 spline axle. Yukon makes a factory replica diff that is a clutch style posi. A set of Moser axles and your good to 700 ft/lbs for miles and miles of abuse. While you're making this upgrade have the axle tubes welded by someone that knows how to do it successfully - it takes a lot of heat (or preheat). A stick welder will work better than a low heat mig. But it can be done with a mig in the correct conditions.

Where are you located?

regarding a factory posi - you won't find one that is in good condition anywhere other than a low mile showroom.
 
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69hurstolds

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regarding a factory posi - you won't find one that is in good condition anywhere other than a low mile showroom.
If you scrounge around like I did, you can get just about every piece new GM (but I wasn't able to find a new carrier housing) to rebuild the 8.5 guts to like new condition.

If you have a worn out posi and need new clutch plate packs, Bruce Ponti had a slew of them made several years ago as a kit. He had a few sets left when I got hold of him and got a set a couple years ago. He designed them to be a bit more durable, but they pretty much are stock replacements for the GM p/n 231127.

Contact:
[email protected]

Never know, he may still have some if you need them.

Of course, if you have 270 bucks plus tax laying around with nothing to do, you can always get that set on ebay...

 
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Built6spdMCSS

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Jun 15, 2012
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S60 is drag car stuff, no need on a street car.

If you already have the 8.5 in the car and it's a street car with light track stuff I'd put in a Torsen style Posi Diff with 30 Spline Axles and whatever gear ratio you want. Torsen style is torque proportioning by design and works great, I've had one in my 9" setup since I bought it in 2007.

If you're an Auto with even 600hp the 8.5" will last a long time. Then again depends on how you drive the car. Street car will work great, something on the track with a Transbrake and big Converter, yea that's different. Standard car with 500hp or more, they tend to beat a drive train to pieces over time.
 
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