Thread: 8" vs. 9"

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Hi Guys,

Since you are all so knowledgable

I would like the pros and cons of the 8" vs. the 9" rearend.


Feel free to throw in experiences and opinions!



Also,what are the opinions of an Auburn Pro Series w/Richmond gears?


TIA

Bottom line the 9" is stronger but it is also heavier and harder to find in narrow widths. The 8" is a good solid rearend for most applications.

In a lot of cases the 9" gives you bragging rights but is overkill in many street applications. If you are running a combination that sees a lot of abuse such as a stick car or a car with a high stall converter and an engine with a lot of torque and sticky tires the 9" is the way to go.

No rearend is "bulletproof" you can break anything if you try hard enough.

I'm running a 9" in my wifes 77 Cobra II with a 302/C4 combination strictly because I had it laying around and for bragging rights. I'm running an 8" in my 77 Mustyang II coupe with a 351/4spd and don't expexct any problems from it even with the bigger engine and stick.

I've had good luck with both Auburn and Richmond. The key is to have them properly set up when you build the 3rd member.

Mike gave you the major part of the picture. I would only add that, typically, with the 28 spline, the stock axle shaft is the weak link. If you take a rear end apart that has had some hard drivin' done to it you'll often see the splines have a bit of a "spiral" to them. This is a precursor to the axle shaft snapping and means the axle shaft should be replaced. I've seen this more often on 9's than 8's, which may not mean anything other than 9's get abused more.

One other note to go with Mike's comment on braggin' rights. I've often heard, or read, where people claim to have a 9" when they actually have an 8". Either they don't know any better, or they're doing the same thing they do about their hp rating.

An 8" will suffice just fine on the street unless you are building a monster....and if you were that question wouldn't get asked <g>..

8" stuff is rapidly getting out in the aftermarket just as fast as 9" component prices are going up...but..

You can still get a 9" housing with axles and calipers cut to any width you want from those boys in east central Illinois (Phillips Street Rod Parts..I think)... It has GM front calipers on it (ie: no parking brake).. You could probably get a discount for getting it with no calipers and add Caddy Eldo.Buick Riv/Olds Toro calipers that have parking brake stuff built in.

9" housings aren't too awful bad....if you shop right.
(type 9" Ford on Eaby and hold on..)

An Auburn posi is a good piece..

Watch the gear vendors on selecting your gears.
Drag race gears are softer (to absorb initial launch impact stresses) and are not as durable as street gears.

I probably spent $1000 setting up my 9" what with the Moser axles and such... I could probably trim a couple hundred off of it by buying that narrowed housing with axles...

Some pics are at:
http://community.webshots.com/album/42740280aaZVkW
and
http://community.webshots.com/album/42709364fffYOh
Hope it helps.
Jeff

Thanks for the info guys!

Just for some backround ,I'm restoring my 65 Mustang.My engine,by initial guestimations will have roughly 400Hp. I have shopped around for a 9" (e-bay too) It's either hard to find or outrageously pricey. I think going with the 8",is what I will have to do. The car has a 3-speed,which I decided to keep until it dies.

So,what do you all think?


Also,does anyone know the bolt pattern of a 8.8" rearend?

Is it the same as an 8"?

So... just how big of a supercharger/nitros shot are you running to get 400 HP?????.

I'm assuming your talking about the 289 you list in your profile. I'm not trying to burst your bubble, but unless your running MAJOR modifications and $, your HP figures are likely about 100+ too high.

If you are serious about the HP, the 8" will be the least of your worries. In reality, the part that will break will be the weakest parts. So in order it will likely be the clutch, U joints and tranny before you break the 8".

Even behind a moderatly modified 289 which is what I assume you really have, the 8" should do just fine.

You can always do as Bob says...........................

"I've often heard, or read, where people claim to have a 9" when they actually have an 8". Either they don't know any better, or they're doing the same thing they do about their hp rating."

Yeah,I think the guesstimations are high also. Hey,I'll be plenty happy with 300hp! When the car is all done I'm going to have it dynoed(is that a word?) A place just opened up near me

Some sanctioning bodies do not allow you to run c-clip axles, so if you want to race, you may have to spend some money on a c-clip eliminator kit. The 9", GM 14-bolt, and Dana 60 all have floating axles, without c-clips.

The 8" rear is usually plenty strong on the street, in most hot rods with a chromed out low compression small block with a stock tranny it will do fine. I bracket raced a Maverick with an 8" and a spool for awhile. Mike is right, I broke a couple U-Joints and tranny and clutch peices quite often (4 speed car) but never wounded the 8".

I know Dave, I used to race a 63 Falcon 289/4spd with an 8". Exuberance is a sure-fire way to find to find out what the weak parts are

deepnhock, the rear axle housing shot made me smile, the gallery shots made me smile REAL big. Thanks, Joe

I always went by the HP of the car,under 300 a 8" will be fine.
Don

Under the heading of, 'Been there and done that'. I'd tell you to look for a '76 to '80 Lincoln Versallis. That is, if you want a bolt in 9", with disk brakes. It seems Lincoln used springs on those cars and they match up to the Mustang springs just fine. The pinion yoke, will probably need work, as may the shock mounts. That's really about it. The one thing you'll learn, is that they are 28 spline and usually high geared, like over 3:00. I in fact have one in the shed, it is a 2:50. Great for Bonneville, but not, for a get out quick, car. That's when you get an Auburn set up, or even a lower stock, open end.
As for the 8", the previous posts are pretty much right on. I am able to get well over 300 horses out of my Stang and with the stock 8" and the C-4, I have never broken anything. I do, however, get lots of wheel spin. That, is probably what saves me. The car barks the tires, hitting second, if I just push it a bit and let the trans, do it own thing.
Just look at the housings, on the two diffs, and you'll see, that the 8" is more of an oval shape. Once you see the difference, they are easy to spot.
Hope you can find something in all that, to use.
TJ

Thanks Joe...
It's supposed to bun, isn't it?
Jeff





deepnhock,
the rear axle housing shot made me smile, the gallery shots made me smile REAL big. Thanks, Joe
Joe Gaddy