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As we all know from forums, this great nation is littered with the remains of thousands of grenaded 8” rear axles who gave their life to provide their owners motivation to swap to a 9” when they accidentally put a 2 barrel on their 200 Inline 6 and overpowered the teeny axle. Everyone would love to have the brawny 9” under their car with gleaming 31 spline axles, but let’s face it. Is it truly needed? I’d like to discuss the merits of keeping the 8”. What are the real weak points of them and where and when do they fail? I bring this up as someone who use to slap M/T ET Streets on my daily driver ‘66 with a stroked small block and hammer on it at the track. My 8” never failed me and never showed signs of premature failure. I’m currently building my ‘66 coupe into a street/track car to toss around the track on weekends. I’m planning to push around 400 at the crank and run a Detroit true trac. I won’t be shocked if I have to pick my 8” up off the track at some point, but for now I’m on the verge of ordering a new nodular center section and heavy duty pinion support to try and beef up the 8” under the car currently. What are your thoughts and experiences? If you’ve had an 8” give up the ghost, what were the circumstances and what actually failed?
 

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The general consensus is that they’re good up to 400 ish.
 

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My Currie center section was one of the last nodular case 8" units they built. They no longer supply the case. When I bought it, I was told that most of the internals (bearings, etc.) are the same as it's 9" big brother. I have all the confidence in the world that i will never break it. Axles may be another story!
 

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My 8 inch has held up through many low 12 and high 11 second runs on the drag strip on 28 x 9 ET drag slicks.

However, I have a 67 case, ARP side bearing studs and ARP pinion housing bolts, I replaced the stock pinion bearing preload crush sleeve with a solid spacer, Toyo bearings, got a new traction loc for it. The engine is now a 331 making something in the 400's at the crank. I haven't run it on anything that I can get horsepower numbers from. I'm running 255/60 ET drag radials on it right now. Still seems to be working fine so far.
 

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This is the same discussion we would have for 289/302 blocks and a T-5 transmission. The real answer is that there is no answer. Some people break them on the street with 350hp. Other people run 11s on slicks, pulling 1.5 second 60ft times with one all season long. I think on a street/strip car you're probably playing with fire but you said you don't mind blowing it up. Here's the thing about it, I might test an 8" out in a sketchy situation but if I'm ever replacing a broken one, it probably won't be with another 8".
 

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I would use the stronger 67 & later waffle carrier. Last December I picked up a slightly used 3.55 LS 8". Talking with a local guy who builds 8 & 9 inches for a gasket, washers and additives told be the only difference between the 8" and 9" differential is the raceway where the carrier bearing seat are very slightly narrower, that's it. The 9" ring gear will bolt onto the 8" carrier. The 8" and 9" use the same 28 spline axles. To me it looks like the 8" is fairly strong.
 

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I’m with woodchuck. The 8” does not have the third bearing on the pinion gear like the 9”.
 

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When starting from scratch Their is no point in spending money to "beef up" an 8" rearend when for just a little more money you can have a 9 inch rear and be done with it. Quick performance has a good price on 9" housing and 31 spline axles using their house brand parts. Also a great time to slightly narrow the housing depending on your wheel choice.
 

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I’m with woodchuck. The 8” does not have the third bearing on the pinion gear like the 9”.
I've never seen an 8" without 3 pinion bearings?

Their is no point in spending money to "beef up" an 8" rearend when for just a little more money you can have a 9 inch rear and be done with it.
Except if you are more into handling/speed than drag race strength. I went for enough strength at lowest weight and beefed up an 8". I even got one of those Currie aluminium cases that now seems to have become nearly unobtanium.

Chock loads are the usual killer of rear axles, not engine power. High rpm clutch dumps, or rear wheel hop at take off are like hitting the transmission parts with an sledge hammer.
 

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now that's dumping some money into an 8". Yep there is a little weight savings with the 8" at about 40 lbs plus they do use a little less HP to turn. Of course you could just use an aluminum 9" third member.
 

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As we all know from forums, this great nation is littered with the remains of thousands of grenaded 8” rear axles who gave their life to provide their owners motivation to swap to a 9” when they accidentally put a 2 barrel on their 200 Inline 6 and overpowered the teeny axle. Everyone would love to have the brawny 9” under their car with gleaming 31 spline axles, but let’s face it. Is it truly needed? I’d like to discuss the merits of keeping the 8”. What are the real weak points of them and where and when do they fail? I bring this up as someone who use to slap M/T ET Streets on my daily driver ‘66 with a stroked small block and hammer on it at the track. My 8” never failed me and never showed signs of premature failure. I’m currently building my ‘66 coupe into a street/track car to toss around the track on weekends. I’m planning to push around 400 at the crank and run a Detroit true trac. I won’t be shocked if I have to pick my 8” up off the track at some point, but for now I’m on the verge of ordering a new nodular center section and heavy duty pinion support to try and beef up the 8” under the car currently. What are your thoughts and experiences? If you’ve had an 8” give up the ghost, what were the circumstances and what actually failed?
i think you are confusing the 8" removable pumpkin with the 7.25 integral pumpkin rear ends. the only 8" rear ends that came behind the inline six was when ford put the 250 into the maverick, and perhaps the granada/monarch.

and while the 6.75 and 7.25 rear ends are somewhat delicate, they can handle more than a six with just a 2 barrel installed.

as for the 8", it can handle decent power in stock form, about 300 on street tires. with a few easy and inexpensive mods it can handle about 400 on street tires, and as much as 375 on slicks, even dropping the clutch at 5000 rpm.

but realize that there are a limited number of those high rpm clutch drops in the rear end regardless of how much you modify it. the same goes for the vaunted 9" as well.

When starting from scratch Their is no point in spending money to "beef up" an 8" rearend when for just a little more money you can have a 9 inch rear and be done with it. Quick performance has a good price on 9" housing and 31 spline axles using their house brand parts. Also a great time to slightly narrow the housing depending on your wheel choice.
actually if you spend your money wisely, you can build the 8" on a budget. for instance if you have good machining skills you can make your own four pinion 8" carrier, and eve include traction loc as well. axles are going to cost the same either way, and the 8" and the 28 spline 9" rear ends use the SAME axles, so upgrades are relatively inexpensive.
 

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When starting from scratch Their is no point in spending money to "beef up" an 8" rearend when for just a little more money you can have a 9 inch rear and be done with it. Quick performance has a good price on 9" housing and 31 spline axles using their house brand parts. Also a great time to slightly narrow the housing depending on your wheel choice.
Agreed. I just built mine with QP. I needed to redo my entire rear, for a little extra money it’s a no brainer to go 9” and be done.


Chris
 

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actually if you spend your money wisely, you can build the 8" on a budget. for instance if you have good machining skills you can make your own four pinion 8" carrier, and eve include traction loc as well. axles are going to cost the same either way, and the 8" and the 28 spline 9" rear ends use the SAME axles, so upgrades are relatively inexpensive.
Nothing wrong with the 8" for a street car, it is a tough rearend. If you are just upgrading the third member for a locker and better gears it is a great way to go. For me though if you are upgrading the axles and spending more money trying to make the case stronger just start with the 9". I did a budget 9" in my Wifes Comet , started with a housing from a 69 cougar for $100 had it narrowed for $100 and found a set of moser axles on craigslist for $275 and a good 3.50 Detroit locker third member for $50.
 

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If you can still find these they are a really nice units with all ARP hardware but they are loud while coasting in corners.
 

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If you plan on slicks at the track and 400 hp, its all about how much money you are willing to put on the craps table. You might be fine but if not, your out big and back to square zero. For a couple of extra bucks and pounds more, you never lose. The only caveat is if you are so close in a class that is so competative that 40 lbs makes a difference and winning is worth the risk.

We aren't even talking about the humiliation of climbing out of your car 10 feet from start with a big mess to be cleaned up while everyone behind you overheats and gives you the stink-eye. If your gonna play - pay. For a street, track or autocross car, I would advocate for a well built 8" for a 40 lb bonus and the extra 3/4 of a hp the 9" because the pinion is at the bottom instead of the middle of the ring gear.
 

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There are a lot of aspects not being discussed here...curb weight of the car makes a big difference in how long a rear end lasts under abuse...also, people are throwing around numbers like 300 and 400HP...but HP doesn't break rear ends...torque does. For instance, with the v6 in my car I could clutch dump at 5000 RPM all day long and never break an 8" if I were making 400HP, because the torque that engine would make(naturally aspirated) at 400HP would be something like 350 ft/lb. That is why people have such different experiences...the torque of the engines involved and the curb weight of the cars those engines are in...it will vary results fairly widely and it will be hard to nail down the limits without listing those specs.
 

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GM used a 7.5" axle in their 350 inch Camaros during the 80's and 90's. Their engineers said either the tires or clutch would slip before the 7.5" exceeded it's torque capacity.
 

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I snapped an axle launching at an autocross at launch a while back. Replaced the axles with Currie street units and its been fine since. I was fighting severe wheel hop at the time. At 350 HP? and 200 tread wear tires I try to be a little conservative at launch.

755718


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