Anyone looking for a nice rear?

Rt Jam

Master Mechanic
Mar 30, 2020
306
63
Ontario Canada
The used 8.5 G body vs brand new Currie 9" bolt is a poor comparison.

8.5's fetch the bucks due to the supply. These are Only found in 442's and Grand Nationals. A true bolt in upgrade for a G body and value to an original GN. Nothing fills the void here making the price solely driven by supply vs demand. I don't care what you bought one for a few years ago. This is only going up starting today.

A brand new manufactured rear should only be compared to Other brand new manufactured rears. We are talking housing, center, gears, bearings, seals, axles, yoke, differential etc. All new and ready for war. Zero comparison to a 30 year old used 8.5".


Just to add to the debate. An S60 is stronger and more efficient than a 9". A 12 bolt GM is lighter and more efficient than a 9".
Ford 9" is only good as a spool. The rear pinion bearing takes up space, making the differential small. In other words clutch style lockers for these are puny compared to 12 bolt, S60 and even 8.5's.
 
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Built6spdMCSS

Royal Smart Person
Jun 15, 2012
2,149
113
Florida Beach
Out of curiousity... are there truely any performance parts for the 7.5" differentials?
The other guys covered it, I've been busy. There are some things out there but it's basically a band-aid on a giant bleeding wound, especially if you make power.

Tore up the rear in several factory stock LS1 Fbodys just putting a tune on them. The right conditions they pop. Those are 28 spline units too.
 
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Ernest

Master Mechanic
Apr 28, 2016
334
63
Texas
Its just the 9" rear build is a wee bit extrevegant for me, for im more on the conservitive side of things when it comes to streetable hotrods, usually 400hp max and naturally aspirated, no power adders whatsoever, just to cruise around, show off from time to time, now the 8.5 rear would do me just fine, but the prices wanted and the scarecity of them. fudgeaboutit
 

565bbchevy

Geezer
Aug 8, 2011
9,196
113
Michigan
For me it wasn't only the high prices they are asking for a used 8.5 I also wanted to run a 3.25 gear and I would probably end up with "while I'm in there" and end up spending more money than I have into my 9-in
 

Built6spdMCSS

Royal Smart Person
Jun 15, 2012
2,149
113
Florida Beach
Its just the 9" rear build is a wee bit extrevegant for me, for im more on the conservitive side of things when it comes to streetable hotrods, usually 400hp max and naturally aspirated, no power adders whatsoever, just to cruise around, show off from time to time, now the 8.5 rear would do me just fine, but the prices wanted and the scarecity of them. fudgeaboutit
Eaton TruTrac Differential, 28 Spline Axles, all I would setup for that power level.
 

Ernest

Master Mechanic
Apr 28, 2016
334
63
Texas
Sounds good.

Now, i've always dreamed of having a naturely aspirated 427cid SBC built, big cubic engine, big money, i know, only because it would be awesome to own and it just so happens to be the same number of my current home adress(fitting), because of that, by all means, in goes that 9" rear with 3.70gear for my 79malibu 2dr coupe, i just have to figure out auto trans for it, because im not even sure if even a built to the hilt 700r4 will last behind it.
 

565bbchevy

Geezer
Aug 8, 2011
9,196
113
Michigan
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Ernest

Master Mechanic
Apr 28, 2016
334
63
Texas
Here i thought 434cid was the largest you could go..... that 454cid in a SBC package is nuts and only for $10k, figured it would be more than that no matter who built it.
 

SS_Malibu

G-Body Guru
Sep 27, 2021
620
93
Mesa, AZ
Well after reading through this thread, I'm a lot more comfortable with my factory 7.5 Posi unit (freeway gears for now) in my '79 Malibu. I have the Blueprint 383 in mine and while it's 450 HP @ 6000 RPM's I'll never take it there. It's just a fun car to enjoy. The mildly built TH350 trans and rear gears will eventually be switched but I get enough enjoyment from it either way. If anything was to break with the trans or rear end then it will get moved up the list. Until then, I'm just gonna enjoy it.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,815
113
To add to the Rt Jam post about supply and demand, first one would need to understand the demand side a bit. While there's many reasons to actually seek one out, it all comes down to this- We all know the supply side is shrinking, but the demand side will always be there because the 8.5 is the better choice over the 7.5 every time. If the consensus didn't believe that, then the price of 8.5s would be about the same as a 7.5.

If you have money to fix it after you break it, then by all means, sky's the limit on rear ends. Nothing can break on your car that you can't get fixed unless you break your wallet or empty the bank account. Then it's an issue. That said, decide where you want to go with the car as far as end plans. If you want a street and highway cruiser behind a 300HP crate engine, don't get the 9" as a 7.5" is less of a parasitic draw, and you shouldn't be tearing up parts.

ROI is king. If you can't get the enjoyment out of the car compared to the $$ tossed in it, why do it? Money well-placed is better than total amount spent. Build with a plan. Whatever works for you. I've seen (and done myself) a lot of stupid spending in my day. People pouring tons of cash into their car and not complimenting the parts that appear to be just tossed together. And with their bank accounts maxed out to buy the most expensive stuff on the internet, they can't afford to fix it if it breaks. So they "baby" their car because it cost them a lot of money to build it in the first place and don't have a lot of money left to fix it should it break. No. If you're building a bullet-proof drivetrain, then I think you should drive it like you stole it. Much more fun. That should be the point of the bullet-proofing, right? On the other side of the coin, there's the show-offs with the modified power-packed engines who try and rip their tires off with their stock 7.5s. They're on borrowed time, regardless of what they do. Then, when the break it, they're acting like that shouldn't have happened. It's funny, sort of.

About tuning an engine and breaking rears on an F-body...lemme tell you something, some engines didn't even need tuning to break the F-body rears. The rear ends in the 4th Gen F-body were crappy right out of the factory. Some of them even leaked just sitting there.
 
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