Another rear end question

FallujahMedic · Nov 15, 2005

How do I tell what kind of rear end I have (8", 8.8", or 9")? on a standard '69 fastback, 3 speed mt, 2.79:1 "conventional" gears. I've been looking over at http://www.currieenterprises.com/cestore/ProductsRE.aspx?id=2085 for rear disc brakes and cant figure out which I need. Thanks

5.0StangRacer · Nov 15, 2005

8" if im not mistaken, 8.8" was much newer and 9" didnt come stock on any mustang I dont think...but dont quote me on that

ttoney · Nov 15, 2005

Plenty of Mustangs did come with 9" rears stock. In 36 years your Mustang could also have a replacement. There should be a tag on the rear (well, if you are lucky, I was) and plug those codes in for us.

Also, there are some decent sites with decodes and identification info.

http://www.ultrastang.com/Rearinfo.asp?Page_ID=1

This is one. I had another really good one but misplaced the link. You can put narrower ones in there and gain the ability to use more B.S. but then you would need to switch wheels.

rbohm · Nov 15, 2005

ok first you likely dont have an 8.8 rear as they were not built untill the early 80's. look at the pumpkin, if the edges are smooth, then you have an 8" rear. if they are bulged around the bolt holes then you have either a 9" or 9 3/8" rear. the 9" rear did come stock on some mustangs, usually mach 1's and boss cars, or big block cars.

now to tell the difference between the 9" and the 9 3/8" rears, if you can put a socket and ratchet on the lower bolt, you have the 9 3/8" rear end.

Edbert · Nov 15, 2005

65-66 only the K-codes had 9s.

67 and up the K, the Boss302 and all big blocks had them.

I'm pretty sure your car came with an 8, early 65-68 6-cylinder cars had 7s, not sure about 69+ though.

But it certainly could have been changed out in the 35+ years since it was born. From the rear 8s look pretty round and 9s are oval.

tos · Nov 15, 2005

I would also rule out the 8.8. But if your tag is missing then the two ways to tell that I use are number one if you look at the back side of the diff housing a 9" will have a raised area for clearance og the ring gear. This raised area will run up and down and can be formed a ouple of ways. I have two 9" rears and they are different. One has a very pronounced "hump" but the other is really suttle because the housing is a little larger and beafier. The 8" will be smooth and may have dimples like some 9's do. BUT the best way for me is to look at the two bottom third member studs/nuts. The nine doesnt have clearance to get a socket and ratchet on them but an 8" does.

FallujahMedic · Nov 15, 2005

Does this help identify it?

FallujahMedic · Nov 15, 2005

anyone?

thehueypilot · Nov 15, 2005

That's an 8".

65up2d8 · Nov 16, 2005

thehueypilot said:
That's an 8".

Dead on.

D.Hearne · Nov 16, 2005

2.79's? That's an 8" for sure. No doubt about it. 9" rears didn't have 2.79 ratios.Nine's came with even number ratios, except for the 3.89's ( 2.50, 2.75, 3.00, 3.25, 3.50, 3.70) And the 8.8 didn't appear till the late 70's or early 80's.

bnickel · Nov 16, 2005

yep that's definitely an 8" rear.

i just wanted to add that starting in 69 all mustangs with 351 or larger engines came with a 9" as well.

d.hearne, i have to disagree about the gear ratios being all even. i believe there was a 2.79 for the 9" but i could be wrong on that one. however my old versailes rear came with a 2.47 diff. i swapped it for a 3.70 before i sold it. and they also came with 3.89's as well

FallujahMedic · Nov 16, 2005

Thanks guys, now I can buy more parts!! The wife complains that all I do is buy parts, the spare bedroom looks like an auto parts store hehe.

Edbert · Nov 16, 2005

Buying parts is better than buying lap-dances right?

At least from her perspective I imagine

Another rear end question

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