JohnVallo
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- Feb 9, 2015
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- Venice, FL
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- John
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- '16 GT350, Shadow Black, Whipple Supercharged
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- #1
I will do my best to explain in detail why the 3.15 ratio setup isn’t compatible or doesn’t interchange with the other higher numerical gear ratio’s (i.e., 3.31, 3.55, 3.73 etc.), setups in the “Super 8.8” rear-end. -What’s Different? -
First of all, the -Bare Housing- in the “Super 8.8”, (the part that holds all the internals, and bolts to the subframe), whether it be aluminum, or cast iron, (ARE ALL INTERCHANGABLE).
Terminology:
If you are referring to the -Bare Housing with everything in it-, this is usually referred to as a “Loaded Carrier”, or “Pumkin”.
The “Differential”, or “Differential Carrier” should only refer to the part that the Ring-Gear bolts to whether it be “Trac-Loc”, or “Torsen” type.
So here are the exact differences between the 3.15 ratio setup, and the others (3.31, and up) in the “Super 8.8” rear-end.
The “Differential” itself is different with the 3.15 than with the others. Why? Read-on
The 3.15 pinion head (the part of the pinion that contains the teeth) is larger, than the others, Why? -It has more teeth- The pinion tooth count on the 3.15 is: 13, The pinion tooth count on the others (3.55, 3.73 etc.) is: 11
Left: a 3.15 Pinion gear: OD at head is: 112 mm, Right: a 3.73 Pinion gear: OD at head is: 98 mm
This larger diameter pinion head presents a problem. The 3.15 Ring-Gear now has to be spaced further away from the larger 3.15 pinion head. How did Ford accomplish this? They used a different Differential, with a different offset.
Left: a 3.15 Trac-Loc Diff., Right: a 3.31, and up, Trac-Loc Diff. The offset difference is: 8 mm
I won’t get into the deeper subject of “Differential Carrier Breaks”, and “Differential Carrier Deck Heights” now, but West Coast Differentials has a good description here:
https://www.differentials.com/technical-help-2/carrier-breaks/
The Ring-Gear’s physical size (in all the Factory ratio’s) are pretty similar in physical dimensions.
All “Super 8.8” Ring-Gears have same ID, OD, and bolt pattern, -they only vary slightly in thickness and tooth count-
Left: 3.15 Ring-Gear, Right: 3.73 Ring-Gear
Ratio, Pinion TC/Ring-Gear TC, Part Number
3.15, 13/41, Ford PN: JR3Z-4209-A
3.55, 11/39, Ford PN: FR3Z-4209-C
3.73, 11/41, Ford PN: FR3Z-4209-B
3.91, 11/43, Ford Performance PN: M-4209-88391A (May be Discontinued)
4.09, 11/45, Ford Performance PN: M-4209-88409A
Aftermarket (Super 8.8) Ring and Pinion gearsets have the following Tooth Counts:
4.11, 9/37
4.56, 9/41
4.88, 8/39
For more complete information on the "Super 8.8" rear-end see:
https://www.mustang6g.com/forums/threads/inside-the-super-8-8-rear-end.150514/
First of all, the -Bare Housing- in the “Super 8.8”, (the part that holds all the internals, and bolts to the subframe), whether it be aluminum, or cast iron, (ARE ALL INTERCHANGABLE).
Terminology:
If you are referring to the -Bare Housing with everything in it-, this is usually referred to as a “Loaded Carrier”, or “Pumkin”.
The “Differential”, or “Differential Carrier” should only refer to the part that the Ring-Gear bolts to whether it be “Trac-Loc”, or “Torsen” type.
So here are the exact differences between the 3.15 ratio setup, and the others (3.31, and up) in the “Super 8.8” rear-end.
The “Differential” itself is different with the 3.15 than with the others. Why? Read-on
The 3.15 pinion head (the part of the pinion that contains the teeth) is larger, than the others, Why? -It has more teeth- The pinion tooth count on the 3.15 is: 13, The pinion tooth count on the others (3.55, 3.73 etc.) is: 11
Left: a 3.15 Pinion gear: OD at head is: 112 mm, Right: a 3.73 Pinion gear: OD at head is: 98 mm
This larger diameter pinion head presents a problem. The 3.15 Ring-Gear now has to be spaced further away from the larger 3.15 pinion head. How did Ford accomplish this? They used a different Differential, with a different offset.
Left: a 3.15 Trac-Loc Diff., Right: a 3.31, and up, Trac-Loc Diff. The offset difference is: 8 mm
I won’t get into the deeper subject of “Differential Carrier Breaks”, and “Differential Carrier Deck Heights” now, but West Coast Differentials has a good description here:
https://www.differentials.com/technical-help-2/carrier-breaks/
The Ring-Gear’s physical size (in all the Factory ratio’s) are pretty similar in physical dimensions.
All “Super 8.8” Ring-Gears have same ID, OD, and bolt pattern, -they only vary slightly in thickness and tooth count-
Left: 3.15 Ring-Gear, Right: 3.73 Ring-Gear
Ratio, Pinion TC/Ring-Gear TC, Part Number
3.15, 13/41, Ford PN: JR3Z-4209-A
3.55, 11/39, Ford PN: FR3Z-4209-C
3.73, 11/41, Ford PN: FR3Z-4209-B
3.91, 11/43, Ford Performance PN: M-4209-88391A (May be Discontinued)
4.09, 11/45, Ford Performance PN: M-4209-88409A
Aftermarket (Super 8.8) Ring and Pinion gearsets have the following Tooth Counts:
4.11, 9/37
4.56, 9/41
4.88, 8/39
For more complete information on the "Super 8.8" rear-end see:
https://www.mustang6g.com/forums/threads/inside-the-super-8-8-rear-end.150514/
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