8.5 10 Bolt Build

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Michael Bennett

Greasemonkey
Jun 7, 2018
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Picked up an 8.5 out of a 442. 3:73 open rear end. Also picked up the rear end out of a nineties cop car with an 8.5, Auburn posi and 2.93 gears. I'm going to use the Auburn for now. Tested it and I got up to 150lbs on the beam torque wrench without it slipping so it should be good. The Auburn is a 30 spline so I'll need some new axles which will be a nice upgrade anyway. This is going in my 80 Malibu/408" small block/TH350.

Does anyone know what a good choice would be for 30 spline axles?

Take a look at the pick of my ring gear. Has a small chip out of one tooth. Pinion shows nothing. Replace or run it?
 

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81cutlass

Comic Book Super Hero
Feb 16, 2009
4,639
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Western MN
Moser sells 30 spline direct drop in axles for $260 on summit.
 
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wskirvin

Master Mechanic
May 22, 2017
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Indianapolis, In
I just had mine rebuilt and went with the Mosier axles. Great price on Summit and direct swap for my new posi
 

Michael Watts

Master Mechanic
Dec 12, 2017
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I run Mosier 30 spline axles in my 1979 Z-28 RS Blown Camaro with a 4 speed .3:42 8.5 rear end.
 

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Michael Bennett

Greasemonkey
Jun 7, 2018
121
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Sounds like Mosier it is.

What does everyone think about the chip in the ring gear? Is it an issue? How did it get there?
 

GuysMonteSS

Royal Smart Person
May 21, 2011
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Kentville,Nova Scotia,Canada
I don't know how that chip got there,but if you are on a budget run it "as is" and see if it makes any noise.
If it isn't noisy,I would run it.
Guy
 
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pontiacgp

blank
Mar 31, 2006
29,270
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Kitchener, Ontario
I can't open the pictures of the crown gear but you might want to get a magnetic particle inspection done to make sure the rest of the tooth isn't cracked.
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
4,639
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Western MN
Differential gears are heat treated, when heat treat happens they are often quenched after they get hot to be hardened. Not only does that make the parts hard, but it creates residual compression stress. Steel that is heat treated can take lets say 80,000 pounds of force per square inch before it moves and doesnt come back (called yield).

The residual compression stress puts lets say -25,000 lbs of force in the surface per square inch. Basically the gear is trying to pull itself inside out (kinda, best way I can easily describe it). That allows 80,000+25,000 lbs, so 105,000 lbs to be pushed on that surface before it moves.

The issue with the chip is it likely could have messed up the forces inside the part and would break easily down the road. Not all heat treated parts have residual stresses, but many do. You have no idea what caused that chip to happen. Even if the gear pattern has no contact in that area, it's a risk you don't need to take. New gears are $125, and are some of the cheapest parts in diff. I would replace them.
 
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64nailhead

Goat Herder
Dec 1, 2014
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I am finally able to open your photos - holy shmoly - games, set, match on those gears - they are scrap.
 
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