[Hubi]

I know there are many tutorials and videos how to recognize 8 inch from 9 inch but more I watch more doubts I have.
I have flat part in the middle of the housing so it should be 8 inch, but also can't access 2 nuts so according to tutorials it's 9 inch.
Can you help me to identify?
It sits in Mustang 66 but I am not sure if it's original one or not.

 

[crjackson]

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Someone will be along shortly to offer advice.

 

[Model A guy]

I've always do a quiky ID by an 8.8 in the gears come out the back and a 9 in come out the front.

 

[Hubi]

So it may be also 8.8 and I have to remove cover to find out?

 

[Grimbrand]

Pretty sure that one's a 9" rear end. It is most definitely not an 8.8.

Once you've seen a few it's a little more obvious. The 9" looks more 'ovaled', at a glance. The 8.8 has a completely different design, and has bolts on the back of the axle housing instead of in the front.

For reference, that's a 9" on the left and 8" on the right.

And this is an 8.8 from the rear:

 

[Hubi]

1st picture you have linked I have seen digging for information and it makes me almost convinced I have 9 inch, but flat part (or maybe I consider is a flat, but it's not) and fact that there was stock 289 engine inside leads me to 8 inch. Factory installed was for sure 8 inch basing on VIN and equipment tag, but it was nearly 60 years ago so everything could happen...

 

[Grimbrand]

1st picture you have linked I have seen digging for information and it makes me almost convinced I have 9 inch, but flat part (or maybe I consider is a flat, but it's not) and fact that there was stock 289 engine inside leads me to 8 inch. Factory installed was for sure 8 inch basing on VIN and equipment tag, but it was nearly 60 years ago so everything could happen...

Your car did not come with that 9", most likely. However, it IS a 9", not an 8" or 8.8, and it's sure not a 7"! =)

 

[Hubi]

Thanks for confirmation and thanks to one of previous owners for an upgrade 😃 Now I just need to rebuild it, but I know what parts to look for

 

[Cobrajet67]

The 7.5" and 8.8" have differential access on the back of the axle housing. The 8" and 9" have access on the front of the axle housing by removing the differential carrier(third member). Like Grimbrand said you definitely have a 9". Without the original tag that came on it you won't know what it originally came out of exactly. The major differences will be the axle shaft lengths/lug patterns, differential type, ring/pinion gear ratio, and the brakes. There are also multiple different size driveshaft yokes. Depending on the vehicle that it originally came out of it can have two different size outer(wheel) bearing housing ends as well. The small ends will be what originally came with a Mustang or other small car.

 

[Hubi]

Yes, I know there are many combinations possible, but at least I know which section of repair kits I have to check - 9 inch. Thanks for helping me to identify my rear end

 

[GypsyR]

Definitely a nine. Clean off the numbers on the front of the pinion area a bit more and maybe it can be identified in a bit more detail. Judging by the silicone squeezed out around where I would personally use a gasket I would expect some non-stock gears might be in there. I'm pushed towards that thought by observation of the rather homemade looking rear sway bar attachments. Looks like a previous owner had some high performance ambitions.

 

[nutz&boltz]

Looks like copper tubing used for the rear brake lines. Better change that immediately for steel tubing, as hard braking pressure (up to 1,200 psi) is very likely to split that copper tubing. nutz&boltz

 

[Cobrajet67]

Looks like copper tubing used for the rear brake lines. Better change that immediately for steel tubing, as hard braking pressure (up to 1,200 psi) is very likely to split that copper tubing. nutz&boltz

Good catch. We missed that in his pics. There is modern nickel copper tubing but what's on the OP's axle definitely just looks like plain copper tube.

 

[Hubi]

There are more surprises in this car 🙄
Brake lines are on the list to upgrade, same fuel line because I already had an issue with that

 

[Hubi]

I did open it to find out what is inside. Gear ratio is 3.89 (35/9). 28 spline. There is marking A134 on both ring and pinion.
Will every rebuild kit fit it ?

 

[Cobrajet67]

What engine/trans is in this car?
3.90 gears are very short/low. Your engine will be revving high with that gearing though you will have really good acceleration assuming that you have enough tire to get good traction. If you only have a 3 speed in the car then any highway driving is going to be making your engine scream for mercy.
Being a 28 spline axle standard case(not a nodular iron one) your carrier bearing size is likely the most common average size but some out there like for the 1966-77 Ford Bronco used smaller id bearings and some full size Ford cars used larger od bearings. 2.892" od carrier bearings with the 1.780" id are the most common.

Before spending $ on this axle you should verify the width isn't too much for the car. Axles came in many differenct widths that varied in fractions of an inch depending on application. This axle may be too wide for a 1965-66 Mustang if it came out of any larger of a vehicle. If anything you generally want a slightly less wide axle. I think the factory width is 57.5".
Ford Differential Builder's Guide (motortrend.com)

https://www.fordmuscle.com/archives/2002/02/nineinch/

 

[Hubi]

This rear end with this gear ratio came with my car when I bought it over 10 years ago. No changes were made up to now. Width is fine because it's running, I removed it for rebuild, no worries it will be too wide.
Car came with 289 and if I good remember 3 speed auto. I did a swap for LS2 with 6 speed manual. Garage where they did that swap messed up so many small details that I was sick of it and locked car for few years. Now slowly starting to get it back to life.
Car is running but rear end is loud so I want to make complete rebuild as part of restoration to finally enjoy the ride

 

[Cobrajet67]

Width is fine because it's running

Just because the axle was physically installed doesn't mean it's a good width for the car. There are only downsides to having an axle that's any wider than stock.

 

[Hubi]

Just checked, it's 57.5 inch

I have found Yukon overhaul kits, but I am quite confused YK F9C (LM603011) and YK F9A(LM102910). Can't find difference between them. Any suggestion which one to take ?

 

[Cobrajet67]

Just checked, it's 57.5 inch

I have found Yukon overhaul kits, but I am quite confused YK F9C (LM603011) and YK F9A(LM102910). Can't find difference between them. Any suggestion which one to take ?

I'm confused how that's possible unless it came out of a rare K code 1965-66 Mustang. Does the axle show evidence of it being shortened or the leaf spring shackles relocated? Idk why someone would have welded sway bar mounts to an original K code axle.