8.5" 10 bolt rear end identification vs 8.2" - Nova Tech
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  #1  
Old Aug 31st, 08, 07:04 PM
fjas70 fjas70 is offline
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Default 8.5" 10 bolt rear end identification vs 8.2"

how do you tell the difference between a 8.2" 10 bolt and a 8.5" 10 bolt??? is there a difference cosmetically??? or is it internally??? i just bought a "8.5" 10 bolt posi" out of a 72 nova for $250 just want to make sure it is what it's claimed to be before i rip out my stock 8.2", well...it's a posi for sure i'm just not sure how to identify the differenced between the 2 rear ends...where does the 8.5" come into play, where is it measured??? any help would be great!!!
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  #2  
Old Aug 31st, 08, 07:40 PM
63gasser 63gasser is offline
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

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  #3  
Old Aug 31st, 08, 08:13 PM
Big Dave Big Dave is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

It has to do with the diameter of the ring gear.

The pinion is the same diameter as the 12 bolt, but the 1972 rear end will have the weaker 28 spline factory axels unless that is an aftermarket Eaton posi in the rear end you bought that uses the 30 spline rear axels that were also used in the 12 bolt.

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  #4  
Old Aug 31st, 08, 10:47 PM
fjas70 fjas70 is offline
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

oh ok, so it is the 8.5"....so is it safe to say that the 8.5" 10 bolt can be just as strong as the 12 bolt??? do you think i got a good deal on it for $250 or did i pay too much???
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  #5  
Old Sep 1st, 08, 07:15 AM
Philip Philip is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

Hard to say. I do not know the market in your area. If it is usable as is then I would say no it wasn't to much. If it already has a posi that would be good. If not when you purchase one go with the 30 spline set up.
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  #6  
Old Sep 1st, 08, 10:23 AM
Big Dave Big Dave is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

The 8.5 "Corporate" rear end was a corporate cost cutting measure to reduce inventory (from two different rear ends with a 10 and 12 bolt to only one 10 bolt). It was done during the first years of the smog era when the compression drop and introduction of EGR valves had cut the motors horse power in half. It was a "compromise" which means nothing was gained. It inherited the weak axels of the previous 10 bolt, but had an upgraded pinion and a stronger bigger ring gear than the previous 10 bolt but smaller and weaker than the 12 bolt (which had an 8.875" ring gear diameter). With the 12 bolt you could run from a 2.56:1 up to 7.17:1 gears; the 8.5" is maxed out at 4.56:1. The 12 bolt had three different diferentials (positraction units). The 12 bolt mounted 2.56:1-2.73:1 rear gears on a two series carrier, 3.07:1-3.73:1 on a three series carrier, and 3.90 and up on the four series carrier. The 8.5 inch uses only two carriers, a two series and a three series.

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  #7  
Old Sep 1st, 08, 12:41 PM
fjas70 fjas70 is offline
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

how much horsepower/torque would the stock 8.5" 10 bolt hold??? and how much would it be able to hold it i were to throw in an aftermarket posi unit with the 30 spline axles??? does anyone know the offered gear ratios for the stock 8.5" 10 bolt out of a 1972 nova???
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  #8  
Old Sep 1st, 08, 12:57 PM
SHIFTY4 SHIFTY4 is offline
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

if you carefully clean the top of the passenger axle tube there'll be a code/number... compare that with what you find on the chart found here http://www.novaresource.org/axle.htm

scroll down for numbers etc...
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  #9  
Old Sep 1st, 08, 02:22 PM
Big Dave Big Dave is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

If you have a question as just how much power your rear end can handle here is a calculator that will tell you just how much stress you are putting upon the axels and differential.

http://www.moserengineering.com/Pages/axletech.html

Knowing how much torque you are applying (this assumes you have perfect traction with only a 10% slippage at your slick) to the axel here is a chart of aftermarket axels listing their failure points (on average).

28 spline axel________1.200" dia. ________ 4,571 lbs.-ft. stock (GM test data)
28 spline axel stub ___1.250" dia. ________ 3,787 lbs.-ft. stock Corvette (Dana 44)
30 spline axel________1.250" dia. ________ 6,473 lbs.-ft. stock (GM test data)
31 spline axel________1.315" dia. ________ 7,000 lbs.-ft. (Ford 8.8" rear)
33 spline axel________1.370" dia. ________ 8,200 lbs.-ft. (GM 14 bolt truck)
35 spline axel________1.500" dia. _______ 9,600 lbs.-ft. (Dana 60)
40 spline axel________1.710" dia. _______ 12,000 lbs.-ft.

Here is a web site with a great graphic that shows why spline count is so important.

http://performanceunlimited.com/docu...axleguide.html


Now bear in mind you must further reduce these figures by an additional 10% because that factory uses a cheaper steel alloy and then relies upon on an induction hardening for case strength at only the bearings. Additionally the total torque load is split by half (you have two axles carrying the load). Because of this my 12 bolt rear end is still together with it's 30 spline axels even though I am routinely hammering it with 7,063 lbs-ft of peak torque (582 cid BBC with 697 peak torque, 2.48:1 first gear in my 4L80E transmission, and 4.56:1 rear axel ratio.) But because I have broken rear axels before (among about every other part in the drive train) I am looking at replacing the rear with a Dana 60 that I recommend to everyone. With it's 35 spline axels stock and 40 spline with the use of a spool; it is virtually unbreakable.

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  #10  
Old Dec 13th, 08, 07:24 PM
grandnash87@comcast.net grandnash87@comcast.net is offline
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

I need to find an 8.5" 10 bolt posi rear end for an '87 Buick GN, any takers?
Thanks
Jes
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  #11  
Old Dec 13th, 08, 08:22 PM
Big Dave Big Dave is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

Look under a Monte Carlo or a Chevelle A or G-body car, as you have a modified four link with coil springs and will need the ears cast onto the top of the housing to work. Those ears are missing from the F and X body cars (Camaro and Nova), as they use leaf springs in the rear (Hotchkiss suspension).

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  #12  
Old Dec 13th, 08, 10:04 PM
brian oneil brian oneil is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

Just remember not all SS Monte Calros came with a posi rear end, so just dont get one thinking it has it in it.
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  #13  
Old Dec 13th, 08, 10:26 PM
Philip Philip is online now
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

GN's and the 442 Olds were the only G body cars that came with an 8.5". The Montes all had 7.5". Purchase carefully, most of the 8.5's you will find for sale have been run hard and will need rebuilt. I purchased one and the only reusable part was the housing. I am still not sure if it will be used in our project Buick as the cost of an aftermarket 12 bolt will be close to rebuilding the 8.5 with new parts.
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  #14  
Old Dec 13th, 08, 10:56 PM
onovakind67 onovakind67 is offline
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

I was rebuilding a stock 12-bolt in a '70 Chevelle with 30 spline axles and measured the diameter of the axle at 1.085". I then measured the 28 spline axles in my extreme power robbing Granada Ford 9" and found that they were 1.170" in diameter.

Why does the change from 28 spline to 30 spline gain you 24% in strength with a 0.050" increase in axle size while changing from a 28 spline to a 31 spline only gains you 34% with a 0.115" increase in axle size? I thought the formula was roughly rated at the 4th power of the diameter.
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  #15  
Old Dec 14th, 08, 06:17 PM
71SS454 71SS454 is offline
 
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Default Re: 8.5" 10 bolt rear end identification vs 8.2"

Just a little FYI. If you go out and pick up an old Dana 60, don't assume that it has 35 spline axles. My Dana 60 is a 1968 model and I'm using the stock locking differential in it and it is a 30 spline axle. Now, newer ones are all 35 spline, but you gotta watch the older ones.

As for the strength of the 8.5, if it's upgraded with the stronger 30 spline axles, or just aftermarket axles that are better material and don't neck down like factory axles do, they they are plenty strong enough for most street and strip cars. Once the axle upgrade is done, the strength difference is negliagble between it and the 12 bolt. If you look at a stock axle, the axle shaft itself is smaller in diameter than the splines are at that end of the axle, that;s the weak link. Aftermarket axles maintain their diameter adding alot more strength, plus better materials. So even if you decide to keep your stock posi unit, upgrade the axles.

As for the GN, it should already have an 8.5 rearend. All Grand National's came with the 8.5.
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