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Discussion Starter · #1 ·
I am looking to "upgrade" the rearend on my '70 Nova restomod. I am building it to be a strong street machine and long distance cruiser. I have already installed an LS 5.3, 4L60E transmission, large front disk brakes, new front suspension, springs and sway bars. Now I am looking at the rearend. Currently, it has a 10-bolt, open differential, 2.73 (?) gears and drum brakes. It works but the gearing is so low that, with the overdrive transmission, the engine is only turning 1200-1300 rpm on the highway and the cruise control randomly drops out.

I started pricing out the necessary upgrade parts (3.40 gears, limited slip, disk brakes, axles, new spring perches...) and I thought, "Wait a minute... There has got to be an easier alternative". With the multitude of GMs out there, there has got to be one with 'the good stuff' that will swap into my Nova.

It's not a power monster and a 10-bolt is probably strong enough but I am looking for ideas and suggestions on something that will slip in without a lot of modification.
 

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Don’t be so quick to toss your 10 bolt. If it is the 8.5” 10 bolt it is every bit as strong as a 12 bolt with a little work.
Good gears, limited slip, weld the tubes and brace the perches and aftermarket axles it will easily support 500hp.

Reach out to member “JBimmolate” he does diffs for a living and knows his stuff.
 

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Stock 1970 Nova won't be 8.5", it will be the 8.2".

Needs to be a late 1972 through 1979 housing for the 8.5" 10-bolt....which can then be upgraded to newer 8.6" status if you chose to do so. The 8.6 is larger 30 spline axles and was stock in 1988-up trucks.
The 8.5/8.6" will handle what you are planning.

There will be no other bolt-in rear axle assembly for the '68-79 Nova, anything from another vehicle will require either welding of perches or shortening/narrowing, or both.
 

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I am looking to "upgrade" the rearend on my '70 Nova restomod. I am building it to be a strong street machine and long distance cruiser. I have already installed an LS 5.3, 4L60E transmission, large front disk brakes, new front suspension, springs and sway bars. Now I am looking at the rearend. Currently, it has a 10-bolt, open differential, 2.73 (?) gears and drum brakes. It works but the gearing is so low that, with the overdrive transmission, the engine is only turning 1200-1300 rpm on the highway and the cruise control randomly drops out.

I started pricing out the necessary upgrade parts (3.40 gears, limited slip, disk brakes, axles, new spring perches...) and I thought, "Wait a minute... There has got to be an easier alternative". With the multitude of GMs out there, there has got to be one with 'the good stuff' that will swap into my Nova.

It's not a power monster and a 10-bolt is probably strong enough but I am looking for ideas and suggestions on something that will slip in without a lot of modification.
8.5" plenty strong for 500-600hp with 4L60. 3.73 gear on TrueTrac diff with 30 spline axles (26" tall tire.) is normal Street setup with auto OD trans setup. TrueTrac is torque sensing non-clutch diff that can't kill you like the clutch/locker type can.
 

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I'm actually dealing with them right now on a new rear for my 55' the prices are excellent compared to many of the others and the quality appears to be excellent. I have not heard any negative things about them for the most part, still trying to talk myself out of it.
Hard to beat and even harder to talk myself out of it. 35 spline axled 9" with fabricated and back-braces housing including perches with the Yukon beast nodular the helical LSD and all the super solid goodies inside, disk brakes with parking all under $3k is friggin' insane.
 

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Hard to beat and even harder to talk myself out of it. 35 spline axled 9" with fabricated and back-braces housing including perches with the Yukon beast nodular the helical LSD and all the super solid goodies inside, disk brakes with parking all under $3k is friggin' insane.
You're not helping me lol
 

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@bruinfan1966 awww, ya just need that little nudge over the ledge... :p DO IT!!! YOU WILL NOT BE SORRY!!!! HAHAHAHA... In all seriousness though, how can you go wrong with a solid build like that good past 1,000 hp/tq?
 

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I'm actually dealing with them right now on a new rear for my 55' the prices are excellent compared to many of the others and the quality appears to be excellent. I have not heard any negative things about them for the most part, still trying to talk myself out of it.
Hey, Even Miles (JBimmolate) recommended them to me... And that's what he does for a living and is less than 150 miles (LOL) from me and could easily have built me one... That cinched it up for me.
 

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Maybe this will also add a little more perspective: I had my 8.5" 10 bolt rebuilt with new gears, bearings including axel bearings. I have a .62 OD so with 3.73 gears and 27" tires I can cruise at 80 at only 2300 RPM. To have the rear rebuilt cost me about $500 parts (JEGS) and labor. For another $500 I could have had the posi unit also installed (I didn't). With your 2.73 gears you should have the right carrier to install 3.42, 3.73 or lower gears. Most OD ratios are around .68 or so, so you could play with a gear/rpm calculator to determine what suits you best..
 

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@Skyline347 I have a 72. It had 10 bolt posi with 3.08’s

When I started math’ing out the cost to really build it, I decided to just pull the trigger on a QP 9”. Being able to swap out center sections is also a huge benefit. With the GM rears, any changes mean the rear has to be torn into under the car. It’s a suck design IMO
 

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Discussion Starter · #14 ·
Stock 1970 Nova won't be 8.5", it will be the 8.2".

Needs to be a late 1972 through 1979 housing for the 8.5" 10-bolt....which can then be upgraded to newer 8.6" status if you chose to do so. The 8.6 is larger 30 spline axles and was stock in 1988-up trucks.
The 8.5/8.6" will handle what you are planning.
How do you visually distinguish an 8.2" from an 8.5"?
 
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