I've been doing some reading as to tell the difference between a 8in vs a 9in rear end. My question for anyone who can answer: What makes an 8in rear end an 8 and what makes a 9in a 9. I know the 9in has an extra gear for support for torque, buy why is it called a 9in?
IF I remember correctly, a gret way to tell is if you can fit a socket on the nuts at the 5:00 and 7:00 of the pumpkin (closest to the ctr section) , it's a 9. If not, it's an 8. or go to www.fordmuscle.com or www.sbfford.com and search, its in there someplace
the ring gear diameter gives it the name. For comparison, the Chevy 12 bolt has an 8.875" ring gear, the Dana 60 has a 9.75" ring gear.
8 inch housings have tappered axle tubes ,but 9 inches out of early Mustangs do to.The best way to tell is what the other guys said about the bolts on the center section .The 8 inch center also looks a little more oval shaped than a 9 inch does ...
Cant say all 8" ers have tapered tubes..My 8" out of a montego does not it is straight all the way out to the backing plates..no taper
I believe mustangs came with the same 8 inch thats under comets and falcons. Excluding the hi-po shelby cars, and maybe k code mustangs, Im unsure about those. The 8" thats in my brothers merc has tapered axle tubes, its an early mustang unit im pretty sure.
Shocked me too ..because most I have seen do have a taper in the tubes..I almost thought I scored a 9"..
6 cylinder early Mustangs were 4 lug 8 inch and the V/8's were 5 lug and the hipos had 9 inch if im not mistaken.They all had the tappered tubes .As far as i know thats the only 9 inch that had tappered tubes...
This is correct ... This is a old junk yard trick to identify a 8 inch Most times, a 9 inch is preferred over a 8 inch. Henry Ford always upgraded his factory vehicles with a 9 inch if the vechicle was over 250 HP or so. A lot of the mid to late 60's Fords could come with either a 8 inchor a 9 inch. Mustangs, Fairlanes and such ... with the small block engines under 250 HP or so got the 8 inch. The higher horsepower ( with more than 250 HP ) got the 9 inch. EXAMPLE = the early Mustangs with the 271 HP high performance engine got the 9 inch ... But the lower 225 HP ones got the 8 inch. Early 9 inch Ford axle shafts are tapered and are really not much stronger than the later 8 inch axle shafts. When Ford came out with the higher horsepower Big Blocks ... Ford had to go to the 31 spline axle shafts ... the regular models still got the 28 spline axle shafts.
Just for the record ..I wasnt talking axle shafts..I was talking axle Tubes I havent pulled the shafts yet so I dont know if mine are tapered as shown above..but the Axle Tubes on my 8" do not have a taper
OK, I just hauled a narrow-width, tapered, 4-lug Mustang rear end home and the pumpkin is marked by the wrecking yard staff as "Mustang Posi". Could that be a "hipo," and what exactly does "hipo" mean in this context?" I ***ume this rear end must be an 8 inch, but were any 4-lug rears 9-inchers? I can't imagine it, but anything is possible.
As I remember, the early Mustang 6 cyl 4 lugs were integral carrier open diff's that disintegrated behind a 289.
Your right Mustang II's were 8inch and 4 lug as well.The best way to tell between an early Mustang and later Mustang II 8 inch is the early one will have the fill plug on the back of the housing and the later will have it on the Center section or "drop out" ,also the early 8 inch will have two dimples on the back of the housing Hump and the later Mustang II's dont ...
Never heard of a 4 lug 9 inch .The early 65-66 Mustang "Hipo" meant it was a factory high performance package.I think it had like 280 horse or so .Not your basic 289 .They arent common nowdays ,so i doubt you will run accross one in a wrecking yard .If its 4 lug and early like i described above with the 2 dimples on the back and the fill plug on the housing i would say its just a basic 6 cylinder 641/2 -66 Mustang rear.I think the 67's and up are wider.Just for reference the early Mustang 8 and 9 inch are the same width as a 57-59 full size and use the same axleshafts and bearings 8 to 9inch .I know because i have a set from an early Mustang in my 57 9 inch .Even use the same bearing retainer plate pattern.As long as they are both 28 spline and the same length the axle shafts between a 8 and 9 will interchange...
The Jalopy Journal
