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Rear Axle Identification
Are their any identifying marks on the axle housing that would indicate if it is original to the Mustang? I am thinking that the axle on my 72 Mach 1 is a replacement.

There should be a tag on the differential housing. Take a look at this sight.


[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
Perhaps this Site will help you, especially if the tag is still on the rear end.



Do the RIGHT thing.
Thanks guys. Of course my ID tag is missing. Figures.


Suggest you determine what the ratio should be (based on the door tag) and do the manual check to determine if the rear end in your Mustang matches what came from the Factory.

The door tag should show the "code" and you can use that to determine what the ratio is. The procedure:

If you have positraction (Traction Loc).

-Raised the two rear tires off the ground, supporting the car with jack stands (block both front tires)

-Make a horizontal chaulk mark on the drive shaft and one at 12 O'clock position on one rear tire

-Have someone to rotate the tire one revolution while someone else is watching the rotation of the driveshaft.

-The rotations of the driveshaft will "tell you" what ratio is in the car. if it rotates 3 times, you have a 3.00:1 ratio. If it rotates 3 1/2 revolution, you have a 3.50:1 ratio.

If you have an "Open" rearend, you will need to divide the revolution by 2 to determine the ratio. For example, if the driveshaft rotates six times you would have a 3.00:1 and so on.

*I would think that if your rear end ratio matches what is on the tag, you probably have the original rear end.

**The other way you can tell is by taking the rear end apart and looking at the casting numbers on the ring and pinion. That information is readily available at several sources.

Hope this helps!


Do the RIGHT thing.
Thanks guys. I know that I have a posi rear with 3.73 gears. The car originally came with 3.25 gears. I wasn't sure if the whole axle housing was original to the mustang because after looking at it a bit, I found that the entire axle was shifted about .75" to the driver side. I was thinking that when this car was restored, a different axle was used. It was sort of a surprise when I pulled the passenger side wheel off and saw a spacer there but not on the driver side.

Oh, I (for one) misunderstood your questionSmile.

I would say that if you pull an axle and find that you still have the 28 splines, it is most likely that you have the original axles and probably housing as well.


Do the RIGHT thing.
Ford used either 28 spline or 31 spline axle shafts with the nine inch, the eight inch came only in 28 spline, as did the majority of nine inch car applications.For the most part eight inch and nine inch car axle shafts will interchange between housings of the same width,spline count and bearing size (ie. 8" 67 Mustang 28 spline axle shafts will work in 9" 67 Mustang housing, etc.).A method to identify 28 spline axle shafts can be by looking at the center brake hub area, a rectangular slot in the center will indicate 28 spline axles.The 31 spline axle shafts will have a different appearance, with one small center chamfer and two outer holes in the center hub, however, 28 spline shafts can also appear like this to, so it does not always indicate 31 spline shafts (see photo below). Early axle shafts of the 28 spline variety cannot be shortened, due to either a reduced diameter between spline end and bearing end (early Mustangs,Fairlanes, Falcons etc.), or because of a tapered shaft which doesn't allow for re-splining (early full size).It appears starting around 1967 the 28 spline shafts became more solid and the shaft diameter increased along the entire length, so shortening is possible and they can be be resplined to their original 28 count.Most 31 spline shafts can be shortened and resplined with no problems.

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