2015 Mustang IRS Components. So it begins.

[edwardb]

Wrapping up the tear down and preparation for the 2015 Mustang IRS parts. Thought I would share a few more things. Got out the scale and weighed some of the parts. The knuckle and hub assemblies weigh 17 lbs each. The cast iron diff weighs 94 lbs all up. It wasn't easy to get the thing to sit still on the scale, but I think this is quite close. The fact that I can lift it (barely...) says this weight is in the ballpark. Multiple on-line sources cite the aluminum version is 24 lbs lighter, putting it in the 70 lbs range. Looking at some threads about the older design, appear both numbers are slightly heavier than before. But not much. Finally, even though I won't use them, weighed the CV axles. 43 lbs between the two of them. The new design is 34 spline at the diff, and 32 at the hub. Pretty meaty.

I managed to spill some of the fluid out the axle holes while moving it around. I'm just not smelling the quite distinctive odor of friction modifier. But the Ford instructions clearly state 3.2 pints (1.5L) SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant and 4 oz. Motorcraft XL-3 Additive Friction Modifier. I'm planning to drain and replace the fluid as specified. This diff is a standard clutch-pack style limited slip setup. A Torsen setup is available only in the 3.73 ratio.

Several have asked if the internals are the same as past 8.8 diff, e.g. ring and pinion, bearings, etc. I can't answer specifics, but I'm guessing the answer is mostly no. In multiple searches, I found Ford referring to this new IRS diff as a "Super 8.8" touting its strength compared to past versions. I found a side-by-side pic of the new pinion gear compared to the old. The new is larger and longer. The slightly heavier weight compared to the past is also a clue.

Several have commented about the geometry of the new IRS, including the somewhat unusual looking links between the upper and lower pivot points. I compared the pics and knuckles now in hand with the pictures and drawings FF has provided of the new design installed. None of these short links are in the FF design. In fact, clearly one of the pivot points looks like it gets cut off the knuckles, as in the picture below. I won't be cutting anything until the kit and full instructions are on hand. But interesting.