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8.2 versus 8.5 gm 10 bolt question

 
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Knarley Darley
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PostPosted: Tue Jul 27, 2010 6:36 pm    Post subject: 8.2 versus 8.5 gm 10 bolt question Reply with quote

I know we have been through this before, but I have a leaf spring 10 bolt in one of my Camaros that I want to change the gear ratio in, and I dont want to take it apart until I have the new gears here. I am pretty sure it is a 8.5" rear end and was wondering if it can be determined without taking it apart. I know some of you guys will know this right off the top of your heads, so thanks in advance. Also I am looking for 308 gears for said rear end, and used would be fine if anyone has any, or 323s.
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clay
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1972 Chevrolet Nova

PostPosted: Wed Jul 28, 2010 4:08 am    Post subject: Reply with quote

The only way I know right off is the pinion size. You will have to remove the yoke and measure the pinion shaft size. The "good" 10 bolts have the same pinion measurements as a 12 bolt whereas everything else is smaller. I looked up the sizes to be sure. 12 bolts and "good" 10 bolts are 1.625" (1 5/8") diameter and others are 1.438" (1 7/16") diameter. At least you won't have to get the stanky stuff on you yet to check Very Happy . Clay
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Big Dave
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PostPosted: Wed Jul 28, 2010 12:04 pm    Post subject: Reply with quote

The 8.5 inch ring gear ten bolt has two squared tabs cast into the bottom of the housing. looks like a bar running across the rear of the housing hidden by the inspection cover. A 3.07:1 gear set, open rear end, is the most common rear end you will find from an overdrive equipped car.

The 8.2 inch rear end has a crease in the rear inspection cover to direct grease to the outer bearings. The 8.5 inch rear end inspection cover is smooth. Here are some pictures of both.

An 8.5 inch ten bolt rear end



and an 8.2 inch rear end:



Big Dave
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Skunkworkx
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PostPosted: Wed Jul 28, 2010 10:47 pm    Post subject: Reply with quote


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Knarley Darley
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PostPosted: Thu Jul 29, 2010 3:32 am    Post subject: Reply with quote

You guys are awesome as usual. Clay had actually jogged my memory when I was changing rear ends the pinion yoke was the wrong style for my drive shaft U joint, so I put a stock 12 bolt yoke on there and it fit, and worked with the stock 67 Camaro drive shaft. I do indeed have the 8.5, and it has a very tight posi unit in it. Will the 12 bolt axle interchange? Or is the spline count different?
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Big Dave
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PostPosted: Thu Jul 29, 2010 3:01 pm    Post subject: Reply with quote

Depends upon the side gears installed in the Posi. The axel splines slide into the side gears. The standard 8.5 inch used before 1994 had 28 splines after that they switched over to 30 spline axels. If you buy a new Eaton Posi you get 400 pound springs with 14 carbon fiber plates, and it can be purchased with either 28, 30 or 31 spline side gears (the 31 spline offering is not from Eaton but a Strange Engineering - Moser custom made part that requires custom axels). The 28 spline axels are stock and the 30 spline axels from a 12 bolt will fit in once you have the right posi in the differential case.

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ericnova72
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PostPosted: Sat Aug 14, 2010 9:49 am    Post subject: 12-bolt axles in 8.5" 10-bolt Reply with quote

The 12- bolt axles will fit with a 30 spline side gear or spool, but there is a catch of you are using the C-clip retention method in a stock open or posi differential. T

The button on the end of the axle is thicker on the 12-bolt axle, once the C-clip is in you won't be able to install the differential cross pin. The difference is about 1/16" IIRC, an easy job to cut the button thinner on a lathe.

First few years of the 8.5" had a ribbed cover like the 8.2" does, at least in some cars. My '72 Nova was 8.5" with the 8.2" type cover.
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Knarley Darley
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PostPosted: Mon Aug 16, 2010 5:44 am    Post subject: Reply with quote

Thanks for all the good info guys. It is definitely the 8.5" probably out of a nova. I have a pile of 12 bolt axles and a drawer full of cross pins. Some of the pins have Two flat sides, and I wonder if this was to clear the thicker ends on the 12 bolt axle. I will mock it up and let you know, otherwise I will just grind the end of the axles a little bit.
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clay
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PostPosted: Tue Aug 17, 2010 11:14 pm    Post subject: Reply with quote

If I remember right, those flats wind up 90* away from the axles when the retaining bolt is installed. I think the flats are to let it come out past the ring gear teeth on some ratios where the ring gets thick enough to partially cover up the cross pin hole. Clay
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Knarley Darley
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PostPosted: Thu Aug 19, 2010 12:14 am    Post subject: Reply with quote

Good call Clay, now that you mention it, I believe that is in fact the case.
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Skunkworkx
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PostPosted: Sun Aug 22, 2010 1:25 am    Post subject: Reply with quote

I've been 1.64 and 11.8 on a 8.2 I also have a friend that was 10.9's on an 8.2. It's just a matter of time Very Happy
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