I have a mustang diff (66). What are the main differences between? Other than having small ratio choice and not many lsd's? Any thoughts
If it has the necked down axle tubes, harder to find hairpin brackets. I just filled mine in with weld.
well both are really good and desirable rears....both have a extra bearing in front of the pinion to give it strength and support. that 3rd bearing reduces flex under hard acceleration. these rears also dont use C-clips like others do to retain the axles.differences are the ford 9 is a bit heavier than the 8. the 8 inch axles are medium journal and 9 are larger. brakes on a 8inch are 10" and the 9 inch have the m***ive 11".
my exp. is the 8 inch uses a sealed bearing where the 9 is a open bearing on the axels, the 8inch goes threw alot more axel bearings for this reason, if you put alot of miles on.have seen alot of bearings replaced on quite a few cars, second the 8s tend to be noisey, not a problem on a open car. i would go for the nine inch.
I've always used 8" rears. Early Maverick, Comet & mustangs 5 bolt hub & have never had a problem in a 2,400 pound car with less than 300 HP.
8" rears are perfect for a mild street car. Gear selection is less than what is available for the 9" but there are still plenty of options. 9" is the performance rear of choice but "performance" is just another word for "expensive" on a street car. I have a 8" in my 32 and it was easy and inexpensive to rebuild it. I bought my gears from Summit for something like $150 bucks. Local shop had the bearings cheap too.
the 8 requires less power to drive, if you don't have high HP ...or even high HP AND slicks, use the 8...
I have to question..... are you making the change just to change it or are you totally looking for a rear end becuase you dont have one? If you already have a 8" and its mounted, fits, and is working, I wouldnt change it just to be chainging it. However, If you have no rear end, Id look for the 9" over the 8".
When back in the 60's ... if Ford Motor Company had a vehicle with less than 240/250 HP or so ... they installed a 8 inch Ford BUT ... if it had more than 240/250 HP ... they installed the 9 inch inch Ford. The 9 inch is way more available ( at least here in the South ) ... POSI's are easier to find ... and aluminum center sections are available ( which makes the 9 inch weigh less than the 8 inch ). My projects always have more than 300 HP, SO ... I always use the 9 inch when possible ... and a aluminum driveshaft too The 8.8 Explorer rear end is also a strong rear end ...
May as well put in the 9 inch if you can. There may be more HP in your cars future .you will be ready for it. Mine? 1. flathead 2. 5 speed 3. 9"
If width is a issue ... the 8 inch can be the most narrow one from FOMCO. The V8 ( 5 lug ) Maverick is 56 inches wide. The most narrow 9 inch Ford is the 57/58/59 Ford p***enger car or the 66 to mid 70's Ford Bronco ( at 58 inches ). The Bronco does have the 5 on 5.5 wheel pattern that so many folks want to use. The 8 inch only comes with the small axle bearing and the 9 inch Ford commonly comes with EITHER the small or the large style bearing ... in most models. There is a new style also. The 8 inch Ford was popular back n the 60's and 70's ... before FoMoCO came out with their AutoMatic Overdrive transmissions. Because most of the factory equipped Fords with 8 inch rears were small, light low horsepower vehicles ... with small wheels ... the gear selections fro the 8 inch are limited. The factory made a 2.79, 3.00, 3.25, 3.40, 3.50, 3.55 and the very RARE 3.80. I have found factory FOMOCO gear sets to be vastly superior to the aftermarket ones ( which do offer a lot more ratios ). The FOMOCO ones run quieter and seem to be a little stronger. The 8 inch has smaller brakes ... than the 9 inch big brother does.
We have a 9" in my high powered '35 sedan...an 8" behind the flathead in Flower's T truck. Seems to work out really well.
One advantage to a Nine Inch housing, is that you are able to remove the the center section and replace your self. Either exchanging the center section with another or have it rebuilt and replace it your self. Saving you some cash! All tho it may cost a bit more to start!
If it's just a cruiser 8" is fine. If you drive like a hooligan you'll want the 9". Not all 9" are created equal either. The typical 9" has a single cross pin driving 2 spider gears in the diff. Clutch drops and burnouts will shear that pin. The better ones had 2 cross pins with 4 gears and will stand up to more abuse.
got a hybrid 8" under my a.....8" center and housing with 9" truck ends, brakes, 5.5 pattern and now strange axles....i've had issues with carrier shims and roll pins , now has a mini spool and stock 2.79 gears. probably going to cut a 9" housing and use my axles and switch due to the easy to find posi stuff for a 9" ....at the time when i built mine , i had some left over stuff laying around , didn't want it to go to waste.......
What is the rear going in? Weight, transmission type (auto or manual), torque, type of tire being used, and intended usage will determine which is best for you. If its a lightweight, relatively low powered car, even with a manual, I would use the 8". If, however, you drive aggressively, plan to race it, or maybe put in a more powerful engine later, I'd go ahead and use a 9". I see you are in Australia, but I would think there are plenty of 9' rears there with all their high-powered (relatively speaking) Ford musclecars of the 70s made there.
The only noisy ones that I have encountered had gears that were not set up properly. Mostly improper pinion pre-load and improper pinion depth. As for the axle bearings, they can be un-sealed by removing the inner seal, making them open bearings.
WOW! So many replies! Never had so many from a thread that i have started! Thanks so much for everyone's advice/opinions/and stories of experience. Few factors- 1966 Falcon (AUS so narrow early model), lo/mild 289, c4 Auto for now possibly 5-speed down the track. Over here Mustang diffs are fair on price $500Aud and bolt straight in so that's what i have had a few times. To find a 9" it would have to be custom made to fit so say hello to at very best $2000Aud. Really just wanted to know opinions on the 8" as it seems to be a reasonably popular diff to use in the U.S. All your answers have helped out! Its basically like this- if i had a 67-76 Falcon over here a good 9" could be purchased for under $1000 and bolt in. So if i get one of those Model Fords then 9" without a question. Early models- unless i'm going nuts and going all out dollar wise 8" is the go-er! Happy Crusin!
all the talk about an 8" Limits your engine size..in a light car I think you will play hell trying to break it.. if its built right and not cobed together,,it should hold fine.. Now im talking Hot Rod..not heavy car. these model A's are light in the ***, chances of spinning the tires is way higher on the list than breaking an axle..and im talking HP above 260, but probably below 400..if you do go above 400 and you can get a 2500 to 2800# car to hook hard enough to break it (if its built right) i'd like to see how you have your suspension set up that a light car would hook hard enough to breakk a Good 8" this doesnt include those people who mash the throttle and pop the clutch , there is some finese in keeping parts where they belong,,out and out abuse will break any thing. even a big 9"
Being in OZ you should look at something different! Toyota HiLux diffs are tough as nails and almost bolt in. They have an 8" crownwheel [ G series ] The XL,XM,XP Falcon diff is 55.9" [ or 1420mm ] wide. The HiLux RN41 diff is 1410mm wide The HiLux RN10 to RN25 is slightly narrower at 1370mm [if you want wider wheels ] They have a 940mm spring platform. They have 5 x 4.5" PCD [ Ford 5 stud ] They have 31 spline axles The HiLux diff also has 4 spider & Posi options Ratios available are from 3.30 to 7.60 [ 4.11 - 4.875 being common ] And they're cheap as chips
And for those State-Side, we've got that same HiLux too. Here it is just called the Toyota Pickup. Oh, and as a builder of some extreme off-road vehicles, I have seen everything broken, including 2-1/2 ton military axles. One common ingredient to all of them was a driver with a demonstrated propensity for breaking things. If you are one of those folks, the true diagnosis of the problem would require no other tools but a mirror.
Haha! Good use of words, I'll use that one day. I normally use the phrase "Lack of mechanical sympathy" or "He couldn't drive a nail into sand"
I got an 65 mustang 8 inch in my 53 stude. Its the perfect width. I've allso got a 67 fairlane 9 inch. Its 1 inch wider on each side. I will be using a 383 chevy engine. I've got brand new brakes and wheel cyl. On the 8 ''. What to do?
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