4.09 Rear Gear Set

[krt22]

Check out the latest FP catalog, looks like 4.09s are now an option

MUSTANG SUPER 8.8" IRS
RING AND PINION SET
PART NUMBER AXLE RING & PINION
M-4209-88355A 8.8" 3.55
M-4209-88373A 8.8" 3.73
M-4209-88409A 8.8" 4.09

http://fordperformanceracingparts.com/download/catalogs/2016_FPP_Catalog.pdf

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[Voodooo]

Check out the latest FP catalog, looks like 4.09s are now an option

MUSTANG SUPER 8.8" IRS
RING AND PINION SET
PART NUMBER AXLE RING & PINION
M-4209-88355A 8.8" 3.55
M-4209-88373A 8.8" 3.73
M-4209-88409A 8.8" 4.09

http://fordperformanceracingparts.com/download/catalogs/2016_FPP_Catalog.pdf

Yep. Theirs another thread

 

[Hi-PO Stang]

Great news ! Now, what is a Super 8.8 rearend ? Do all Mustangs have the Super 8.8 or is that an option ?

 

[krt22]

the super 8.8 is the rear end found on the S550 cars with IRS.

 

[EXP Jawa]

The Super 8.8 is the beefed-up version of the 8.8 that is used in the S550 across the board. The pinion is beefier, the bearings are bigger, the differential itself is longer with a bigger bolt circle for the ring gear. The axle shafts are upgraded from the old 8.8's 31-spline to 34-spline from the 9.75" axle. Actually, the Super 8.8 is, essentially, a hybrid of the old 8.8 and the 9.75.

 

[Hi-PO Stang]

Interesting that Ford would call the IRS a Super 8.8. So the V6 Mustangs also have the Super 8.8 ?

 

[EXP Jawa]

There is only one axle size for the S550. Ford calls it a "Super 8.8" because it still uses an 8.8" ring gear, but the assembly as a whole is strengthened. The IRS aspect has nothing to do with it; they could make a live-axle version and it would still be a Super 8.8" axle. In fact, I heard tell that there actually is a live axle version for the Transit van, and that was where the 4.09:1 gear set came from. But that is not confirmed.

I should point out that while all S550 cars have the Super 8.8, there are different versions of it, with higher stress applications getting an iron carrier. Lighter duty versions are aluminum.

 

[Hi-PO Stang]

Thanks for the explanation. I suppose Ford would call a possible stronger version in the future a Super Duty 8.8.

 

[mustang_guy]

There is only one axle size for the S550. Ford calls it a "Super 8.8" because it still uses an 8.8" ring gear, but the assembly as a whole is strengthened. The IRS aspect has nothing to do with it; they could make a live-axle version and it would still be a Super 8.8" axle. In fact, I heard tell that there actually is a live axle version for the Transit van, and that was where the 4.09:1 gear set came from. But that is not confirmed.

I should point out that while all S550 cars have the Super 8.8, there are different versions of it, with higher stress applications getting an iron carrier. Lighter duty versions are aluminum.

The auto gt get the weaker aluminum housing where the manual get the iron. Kelly at bmr broke his aluminum housing.

 

[Hi-PO Stang]

So the auto trans Mustangs get aluminum IRS. Do the auto trans Mustangs have the aluminum IRS to offset the weight of the heavier auto trans ?

 

[wproctor411]

Had to:

 

[krt22]

yeah strange they could not have made it the popular and well known 4.10

 

[Nataphen]

I'm interested to see the acceleration difference with these in the GT350.

 

[arsenalrocks]

nice find, may consider this mod for faster acceleration.
so how does it work exactly? dose the entire diff need to be disassembled? and replace the 3.73 ring/pinon set with the 4.09?

I saw they have the installation kit, bolt kit, and seal kit as well for that, do I need that too?

lastly, is it DIY friendly?

 

[Voodooo]

nice find, may consider this mod for faster acceleration.
so how does it work exactly? dose the entire diff need to be disassembled? and replace the 3.73 ring/pinon set with the 4.09?

I saw they have the installation kit, bolt kit, and seal kit as well for that, do I need that too?

lastly, is it DIY friendly?

The whole diff needs to be taken apart. It's not hard to do if you have the correct tools. I've done 100s of them, you need a press and dial indicator. Also a torque wrench and inch pound wrench.

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