8" Rear Behind 428 on the Street--Will it Live?

[67xr7cat]

Depends on how much traction you have and how hard the clutch grabs. A clutch that hits hard will break just about anything.  A factory 428 car had big input/big output toploader, a 9" with N case. daytona pinion support and 31 splijne axles. Also had bigger u joints.  So with the right clutch, regular street tires, and some sane driving if the 8" is in good shape I'd say will live awhile.  that said I'd have on the future upgrade list at least what a 428 came with stock.

[410bruce]

Wow guys, thanks for all the replies, was not expecting it.

Okay, overwhelming consensus is, bad idea. Do not use unless soft pedaling or driving like grandma. Check. 
Richard, Thank you for the offer, I will keep you in mind if something local doesn't show up.

Your guys stories made me think of one. Back in the '80s, a friend had a '67 Mustang coupe with a built 289,  4-speed--can't remember if it was a T-10 or Toploader--with a 4:11 traction lock 8". Well, after several years of abuse the 8" did let go. Pretty sure the pinion exploded. One too many 7000 RPM clutch pops. lol.

Thanks again!

[e philpott]

1971 429 mustang, aluminum CJ heads , Comp 294 S drove several spirited years before switching to a 9 inch on a customer 71 Mustang originally a 302 car , never hurt it despite multiple one wheel peels every time he drove it .

[gt350hr]

    Bruce,
      The axles , side gears , spider gears and cross shaft are all the same 8" or 9" . YES the pinion is smaller and a potential failure point. BUT if you change the crush sleeve between the two pinion bearings to a solid spacer , the durability improves dramatically. Not to that of a 9" but certainly enough to work along with some respectful throttle application.

[Falcon67]

We got about 800 rounds out of a 4.11 8" running on slicks, automatic, 400+ HP.  Eventually broke the pinion gear.  Switched to 9" center with same 28 spline axles, got almost another season before breaking an axle.  Went to 31 spline and no more problems. 

With a 4 speed and that torque, no - go for the 9" now and remove a potential problem area.

8" 4.11 pinion center, 9" 4.11 on the right:


When torque is applied, the main caps tend to want to spread.  Those bitty teeth on the 8" will snap if the applied force moves too far out from the root of the tooth.  I built a 9", C7 stock case (not N), 4.56 Richmond gears, 31 spline Mark Williams Masterline axles and that has been in the car since 1999.  Thousands of rounds with all kinds of power, slicks, high stall converters, etc.  Parks look just fine after all that abuse.  If you really make power and use slicks, then you could consider something like a Strange iron case, which is affordable and way more stout than a old stock N unit.  I have one on "my list" but the deburred C7 cases haven't failed me yet.  If I got close to 600HP, then it's be a requirement.  Right now at around 460 HP that rear is just loafing.  I can run 4 passes in a hour at then thing doesn't even get warm.

[My427stang]

Trick Flow 500-550 HP 428 will beat that 8 into dust pretty quick, however, run it if you want at the beginning, just don't put a penny in it, you are tossing it out the window

When it breaks, preferably before, build a 31 spline 9 inch, weld/box the spring pads, and it'll be fun and reliable after that

[410bruce]

Awesome, thanks again, guys. There's plenty to do on the car to get it even road worthy as it sits so, I'll leave the 8" in for the time being and just use it to get the car around, while I budget for a 9" swap. 

[TomP]

If you want cheap an Explorer 8.8 is plenty strong.  On my 65 Falcon i had a 3.55 geared 8" and broke the caps off the back, with a 200 six and automatic! Yet i had a guy come to me looking for gears in the 3.7 to 4.11 range and an 8" posi unit for his street rod. It had the stock 2.79 open diff and he was looking to race it at the Oldies drags and not cross the line half way through second gear in 14 seconds.
 Turned out this street rod is a 4500lb 48 Buick with a 500" Caddy engine.... and a Maverick 8"... and huge 15" tread width,  33" tall Mickey Thompson Sportman tires. I didn't have the gears and have never had an 8" limited slip but just amazed that heavy car hadn't broken the rear end.

[gt350hr]

   Some people can break an anvil with a rubber mallet. Others can drive cross country with a shoe string as a fan belt. I've never broken an 8" when I've owned one. I've built plenty of them too and never had one fail. NO it's not a nine inch but if respected , it will do it's job.

[e philpott]

The roundy round guys used to buy any 8 inch gears I had back in the 90's  , not sure what class ( Hobby Stock ? )they raced but it was a popular rear unit and I was surprised they were desireable  , not sure if if it's still that way

[gt350hr]

   As I mentioned  , the only downfall is the crush sleeve that allows "pinion walk" . The more substantial 9" gear doesn't fail as easily but still suffers from the crush sleeve. If it eliminated in either diff , the "life" goes up dramatically.

[driveamerican]

I had one behind a 390 c6 in a 64 fairlane and the guy that sold me the assy told me if I could kill it with anything but slicks he would build and give me the 9 inch replacement when I sold the car it still had the 8 inch

[cammerfe]

I had an 8" behind a '79 Mustang with a turbo'd 2.3 that had some work done---including spray. The car would have no significant trouble with small-block 'vettes. I never had any difficulty with the 8". I WAS very leery of the 7.5 that the car came with.

KS