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 convert to posi? 
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Joined: Mon Jan 26, 2009 8:57 pm
Posts: 283
Location: York, Pa
Post convert to posi?
have the rear of the 3rd gen mostly torn apart for a LS1 rear disc upgrade, and got to thinking about just pulling the entire rear out of the car and cleaning/painting it. While it's out it would be a good time to upgrade from the open rear, just not sure it's worth the $400+ diff cost to install a posi, along with the extra work/hassle. Car is a cruiser, i have the GTO to beat on if i want to. Need to stay with a 3rd gen rear, 4th gen rear swap would push the tires out. Thoughts?


Sun Jan 29, 2017 12:22 pm
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Joined: Sun Jan 25, 2009 2:00 pm
Posts: 2696
Location: Lumberton, NJ
Post Re: convert to posi?
Hunt down a 9 bolt. Best 3rd gen OEM rear and fairly cheap. Obviously you'd have to put your back together for now.

If you keep the 10 bolt Yukon gear makes a nice diff. Before you paint it I would have the axle tubes welded also. But if it's out, may as well clean it up and do it right.

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Sun Jan 29, 2017 1:16 pm
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Joined: Mon Jan 26, 2009 8:57 pm
Posts: 283
Location: York, Pa
Post Re: convert to posi?
i'm tied to the 10 bolt - already have everything to convert it to LS1 Rear brakes. looked for a good 9 bolt, but prices shot up on them, and parts are harder to find. I'll (likely) never beat on this car, so a 10 bolt will more than handle anything i would throw at it.

looks like amazon has the best price for a yukon - https://www.amazon.com/Yukon-YDGGM7-5-3-28-SM-Duragrip-Differential-Spline/dp/B0078U9UOW what's the welded axle tube mod? benefit?

from a driving standpoint, will i really notice the difference between an open or posi diff?


Sun Jan 29, 2017 4:02 pm
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Joined: Sat Jan 24, 2009 7:49 am
Posts: 1696
Location: Danville, PA.
Post Re: convert to posi?
I had a local company ( in Danville) put the ten bolt I built in a jig and weld the tubes. They were not square and needed a little a adjusting.
the benefit is the tubes are only welded in two spots on the tubes and basically pressed in.

Tom

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Sun Jan 29, 2017 9:37 pm
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Joined: Sun Jan 25, 2009 2:00 pm
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Location: Lumberton, NJ
Post Re: convert to posi?
I don't think you'll gain much from going to a 4th Gen rear, and yes, they stick out about 1.5" on each side of a 3rd gen. Get a good diff, weld the tubes, get a rear end girdle and you'll be fine. Although, that won't be cheap either. I've just always been partial to the 9 bolt because I don't like C-Clip axles

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9/11/01 NEVER forget!
1988 Trans Am GTA Resto-Mod project *Coming in 2018*
2001 Formula Firehawk #293
2002 Trans Am MRM Convertible
2002 Trans Am WS6 #206 346CI of unbridled fury *gone 4 ever*


Mon Jan 30, 2017 1:22 am
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Joined: Tue Jan 27, 2009 1:50 pm
Posts: 1038
Location: New Ringgold, PA
Post Re: convert to posi?
There was a guy on one of the third gen FB groups who was taking Exploder 8.8's and making them work for third gens for relatively cheap. I did a quick Google search and couldn't find it, but that would be the route I'd look into first if I were upgrading the rear. A friend of my just installed a Quick Performance 9" in his 85 IROC as well. Quality unit.

But, if you won't beat on the car or add power, I'd let it go unless you can score a good/cheap 9 bolt since as Nick said, those c-clips can give you a really bad day lol.

Good luck! LS1 brake upgrade = :thumb

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Wed Feb 01, 2017 8:49 am
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Joined: Mon Jan 26, 2009 8:57 pm
Posts: 283
Location: York, Pa
Post Re: convert to posi?
after looking at it, it'd be close to a grand for parts and labor - i'll punt till i blow it up (unlikely) or want a change. that money can be better spent on the GTO right now.


Thu Feb 09, 2017 8:51 pm
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