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Old 03-30-2011, 11:58 PM   #1
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Default 3rd gen 8.5" strength and compatibility?

I tried a search and didn't come up with anything.

Can you guys answer a couple of my questions please.

Is the 8.5" strong once built, close to the ford 8.8"? I am under the impression it bolts right in but is narrower.. If yes to both of the above questions why is it not more common that people use it in our 4th gens?

I have a buddy that wants my spare 7.62" rear that has a 3rd gen, so I was thinking of building his 8.5" and putting it in my car and buying wheels with the right offset.

Can anyone provide insight as to why this is a good or bad idea?
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Old 03-31-2011, 02:46 AM   #2
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I had an 8.5 in my old 86 iroc the parts came from a friend that had a TQ arm set up in his GN i used the bracket that bolted to the rear and the cover mounted to it. The 8.5 is the ONLY strong 10-bolt made such a shame GM only used the car style from 72-81 in the f body........i was going to build another 8.5 but using an 8.8 is much more cost effective due to the available gears 3.55/3.73/4.10 whereas most 8.5 rears only have 2.56/2.73/3.08/3.42 both rears are quite strong.
The 8.8 has 28spline axles and also come in 31spline in some other vehicles and larger for aftermarket setups.
The 8.5 has 28 spline and can be upgraded aswell to 30spline+ so if you find deals either rear will handle ALOT!
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Old 03-31-2011, 09:17 AM   #3
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I had an 8.5 in my old 86 iroc the parts came from a friend that had a TQ arm set up in his GN i used the bracket that bolted to the rear and the cover mounted to it. The 8.5 is the ONLY strong 10-bolt made such a shame GM only used the car style from 72-81 in the f body........i was going to build another 8.5 but using an 8.8 is much more cost effective due to the available gears 3.55/3.73/4.10 whereas most 8.5 rears only have 2.56/2.73/3.08/3.42 both rears are quite strong.
The 8.8 has 28spline axles and also come in 31spline in some other vehicles and larger for aftermarket setups.
The 8.5 has 28 spline and can be upgraded aswell to 30spline+ so if you find deals either rear will handle ALOT!
Cool thanks for the info, I figured if the GM 8.5 bolted in without modifying it it would be much cheaper to do... I am trying to get away with not cutting up and welding up a rear, I dont have all the tools to do that.
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Old 03-31-2011, 11:23 AM   #4
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Are you talking about a Dana 44?
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Old 03-31-2011, 04:44 PM   #5
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Are you talking about a Dana 44?
I am referring the the GM 10 bolt 8.5" rear that came in 3rd gen F body cars. Those aren't dana's are they? I really don't know much about older cars and different rear ends and what they came in.
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Old 03-31-2011, 05:16 PM   #6
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Third gens did not come with 8.5's. They came with a similiar 7.5 as the 4th gens.
There were a small number of some special Trans Am that came with the Dana 44 8.5, and the Dana 44 was supposedly a warranty replacement for third gens. And I've heard at some point summit used to sell them as a bolt in upgrade.

The point is, finding a third gen with an 8.5 is extremely rare.

Second gens had the 8.2 until 1973, then they got the GM 8.5 with leaf springs.

This is a Dana 44 in a third gen.
Click the image to open in full size.
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3rd gen 8.5" strength and compatibility?-reardifferential-dana44-4.jpg  
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Old 03-31-2011, 08:07 PM   #7
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The dana44 was all that rear was ever called or referred to as. The 8.5 was always the GM 10-bolt....i wish GM would have kept that sucker!
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Old 03-31-2011, 08:31 PM   #8
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Quote:
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The dana44 was all that rear was ever called or referred to as. The 8.5 was always the GM 10-bolt....i wish GM would have kept that sucker!
No, the GM 8.5 is usually referred to as the corporate ten bolt. Somewhere in the 90's it turned into the 8.6 and they are made by AAM.

The Dana 44 is an entirely different rear. It has an 8.5" ring gear but if any part of it interchanges with the GM 8.5 it's totally coincidental.
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Old 04-01-2011, 11:48 AM   #9
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Okay thanks for the help guys, I was for some reason under the impression the 3rd gen had a 8.5"
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Old 04-01-2011, 01:06 PM   #10
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Yep, 3rd gen rears are only good for exploding, just like a 4th gen rear. Even if he has a Dana 44 or 8.5 under the 3rd gen, it will be 2" shorter per side and will require you to run wheel adapters if you put it under a 4th gen.
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Old 04-01-2011, 03:04 PM   #11
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Yep, 3rd gen rears are only good for exploding, just like a 4th gen rear. Even if he has a Dana 44 or 8.5 under the 3rd gen, it will be 2" shorter per side and will require you to run wheel adapters if you put it under a 4th gen.
Thanks for the info, I don't mind the length being wrong I would buy wheels with the proper offset for that. So okay that answers all my questions then.
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Old 04-01-2011, 03:22 PM   #12
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friend of mine has that 8.5 rear in his 3rd gen and its a borg warner rear ( stamped on the housing ). Its held a 383 with heads n cam and a 200shot on slicks with a 5 speed maual and lots of wot launches on the gas for several years, all stock internals.
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Old 04-01-2011, 04:12 PM   #13
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If you are talking about the BW 9 bolt, they are decently strong, but they will pop, eventually. They are only marginally stronger than a 10 bolt. The one in my '89 Formula bit the dust while the previous owner still had it. I had one in my '88 Formula, decent rear end, but next to impossible to find parts for when they blow up.

The only guarantee is to go with a tried and true rear diff. My 10 bolt gov-loc from a S10 held up behind a 350/383/6.0 as well, but it just crapped all over and runs like a open diff now. It's hit and miss, but they do go, eventually.
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Old 04-01-2011, 06:43 PM   #14
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The GM 8.5 or 10 bolt corporate would have been an awesome factory upgrade for a F body. That rear has done amazing things for Buick Grand Nationals, and T Type's. I have one in my 85 cutlass and with stock everything it would cut 1.5x's all day long back in the day. I think when I get that car back out one day I am probably gonna put 4th gen disc brakes on it and keep racing it.

There have been plenty of 8.5's in the 8's at well over 140 mph. The Great Pumpkin ( an orange GN) ran 8.90's at 154mph leaving the hole on the bumper. It had a 33 spline spool, moser axles, C clip eliminators, and a guirdle with STOCK 3.42 ring and pinion, and it cut consistent 1.32 60's

http://www.gmhightechperformance.com...ure/index.html
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Old 04-01-2011, 07:56 PM   #15
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The GM 8.5 or 10 bolt corporate would have been an awesome factory upgrade for a F body. That rear has done amazing things for Buick Grand Nationals, and T Type's. I have one in my 85 cutlass and with stock everything it would cut 1.5x's all day long back in the day. I think when I get that car back out one day I am probably gonna put 4th gen disc brakes on it and keep racing it.

There have been plenty of 8.5's in the 8's at well over 140 mph. The Great Pumpkin ( an orange GN) ran 8.90's at 154mph leaving the hole on the bumper. It had a 33 spline spool, moser axles, C clip eliminators, and a guirdle with STOCK 3.42 ring and pinion, and it cut consistent 1.32 60's

http://www.gmhightechperformance.com...ure/index.html

try that with a TQ arm and it will scream worse than a 12 bolt
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Old 04-01-2011, 10:31 PM   #16
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I could care less what it sounds like with the wheels 6' in the air. If your worried about having a quiet noise free car drive a prius. LOL.
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Old 04-01-2011, 10:31 PM
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