Keep 8" or go 9" in 66 fastback

JDM4401 · 03-22-2011, 12:35 PM

I currently have the 8" 3.00:1 open carrier rearend out of the car to clean up the underside and paint, along with new rear drop leafs. I can't decide whether to keep the 8" and rebuld it with steeper gears or find a 9" that will work.

I plan on rebuilding the engine for the car at some point, but I doubt it will make over 400hp to the rear wheels. I have read that the 8" can handle that power, it that correct?

Are there parts available for the 8" like the 9"? I definitely would want to install a trac-loc and new gears.

66stang289ci · 03-22-2011, 01:18 PM

I think you're 8" should be fine. I have a built up 289 in my car and just installed a posi pumpkin that is rated at 450hp. I doubt you would need a 9" its overkill in my opinion.

Check out ebay people sell rebuilt 8" pumpkins with a posi in it and you're choice of gears.

frdnut · 03-22-2011, 01:57 PM

Your hp level is just part of the equation..How do you use the car?..If your running a manual trans and slicks at the track you could still break it..If its strictly a street car with street tires and an auto trans you should be fine with the 8 inch..

22GT · 03-22-2011, 01:59 PM

Yes, anything you can get for the 9", you can get for the 8". In some cases, they are even the same parts.

silverblueBP · 03-22-2011, 02:05 PM

Quote:

Originally Posted by 66stang289ci

I think you're 8" should be fine. I have a built up 289 in my car and just installed a posi pumpkin that is rated at 450hp.

Why did you install a GM rear in your Ford?

67FSTBKRestoMod · 03-22-2011, 02:57 PM

How bout an 8.8?

Fstbk · 03-22-2011, 04:00 PM

I am in the same boat. I have been pondering a heidts with a 9" for sometime now, but I keep coming back to the 8". But, by the time you rebuild an 8" your still $800 into it, add in new leafs and some decent Koni's and you are over $1200 fast.

I just cant get past having a panhard bar, it moves the body left and right as it goes up n down.

JDM4401 · 03-22-2011, 05:52 PM

I found an article today that said you can use all the brake components from an 8" on a 9". If that is the case, than I can get a correct 9" housing on the web rather cheap and get new axles. Third members don't seem to hard to find. Are the shorter axles easily obtainable from one of the manufacturers that make 9" components? When I refer to shorter axles I mean for the 65/66 stang.

John_Del · 03-22-2011, 06:00 PM

I decided to keep my 8", but I bought a junkyard center section with the improved case waffleing from a 70 something Ford truck as mine has the weaker case.

John

MrFreeze · 03-22-2011, 08:14 PM

Quote:

Originally Posted by JDM4401

I found an article today that said you can use all the brake components from an 8" on a 9". If that is the case, than I can get a correct 9" housing on the web rather cheap and get new axles. Third members don't seem to hard to find. Are the shorter axles easily obtainable from one of the manufacturers that make 9" components? When I refer to shorter axles I mean for the 65/66 stang.

If you get a 28 spline 9" 3rd member, you can use the 8" axles.

MrFreeze

Fstbk · 03-22-2011, 08:52 PM

Quote:

Originally Posted by JDM4401

I found an article today that said you can use all the brake components from an 8" on a 9".

I am in the same spot...
I think that only applies to same bearing sizes. If you have a small bearing 9" you can use your 8" backing plates, but most 9" rear end housings are big bearing?

kenash · 03-22-2011, 09:01 PM

Quote:

Originally Posted by JDM4401

I currently have the 8" 3.00:1 open carrier rearend out of the car to clean up the underside and paint, along with new rear drop leafs. I can't decide whether to keep the 8" and rebuld it with steeper gears or find a 9" that will work.

I plan on rebuilding the engine for the car at some point, but I doubt it will make over 400hp to the rear wheels. I have read that the 8" can handle that power, it that correct?

Are there parts available for the 8" like the 9"? I definitely would want to install a trac-loc and new gears.

Hey Bud,
It's not the HP that kills, it's the "RWTQ". Don't waste your money, like so many others, on 9" when it's just a "braggin" rights. It take's over 400 RWTQ with sticky tires to break an 8" with a nice locking gear-set. Put your dough somewhere else.
Happy Motoring!

MrFreeze · 03-22-2011, 09:53 PM

Quote:

Originally Posted by Fstbk

I am in the same spot...
I think that only applies to same bearing sizes. If you have a small bearing 9" you can use your 8" backing plates, but most 9" rear end housings are big bearing?

I had a '57 Ford rear end in my '66 fastback for years, and the stock brakes bolted right up. Not sure about "big bearing," but it did have much larger axle tubes that required bigger u-bolts and some new holes in the mounting plates. Maybe there are different sized end flanges on the various 9" rears?

MrFreeze

Fstbk · 03-22-2011, 10:20 PM

Quote:

Originally Posted by MrFreeze

Maybe there are different sized end flanges on the various 9" rears?

MrFreeze

Yes, I think there are. I am no expert but learned a bit about the flanges last week in another thread when I was considering a housing from an early bronco, it was a large bearing rear end with 31 splines etc.. I could have used my axles and found a 28 spline third member, but my 8" backing plate bolt pattern was different from what I read on-line. However I have not actually tried it in the real world, hopefully someone can elaborate more.

66stang289ci · 03-22-2011, 10:27 PM

Quote:

Originally Posted by silverblueBP

Why did you install a GM rear in your Ford?

I didn't its an 8" by pumpkin i meant center section