You guys don't play hard enough. The ring gear on Dad's truck (9") was worn out when I got it. And the gears on Rusty (9") were grenaded. Further, we have a guy on the 80-86 forum with broken gears in a 10.25" Sterling. Reported in this thread. It is his work truck and, according to him, he never beat on it.

 

Those look a lot like the rear gears on my wife's Sienna after the pinion bearings came apart. Roller came out as the bearing came apart and munched up the gears. Is that what happened to this one?

The Ford 9" rear differential has been used in drag racing applications for much longer than I've been alive. If the gear size was the limiting factor for torque application this wouldn't be possible.

 

I don't know what the cause of the broken gears was, nor does the pro that rebuilt it. The problem was that the damage was so extensive that everything was damaged - bearing, gears, etc.

Regardless, gears break - contrary to what several have said here. The above picture proves it, as do my experiences.

 

Another mistake I see (I think) in the literature is the 8200 lb GVW listing. IIRC 7850 is the top GVW for '15.

 

So, to restate what was discussed in another thread for posterity...

From what I can tell all trucks with the 3.5L EcoBoost engine get the 9.75" rear differential. My truck built 2/2015 has the 9.75 with the base payload package and regular towing package. Running the VINs of various trucks on FordEtis home page shows the 9.75" axle for every 3.5L EB truck I could find.

It also appears that all other engines come with the 8.8" axle unless equipped with the HD payload package. The E-locker appears to have nothing to do with this, as it's available on the 8.8" axle for trucks with all engines except the 3.5L EB.

In summary: If you want the 9.75" axle you need the 3.5L EB or the HD payload package. All others appear to get the 8.8.

 

Thanks for clearing that up. So, the 3.5 EB puts out more torque than the 8.8 can handle?

 

Perhaps under certain circumstances. The 6R80 has a really short first gear, and applying 420 ft-lbs after torque converter multiplication to a 4.17:1 first gear can generate a LOT of torque to the rear axle. Substantially more than the V10 in my old Excursion ever could, and that had the 10.5" full-floating axle. My '13 would handily spin the tires in first gear with 12,000 lbs behind it.

Five months after participating in the Ohio meet in 2013 my axle developed a whine and had the ring and pinion replaced under warranty. I'm not sure if the two are related, but axle issues sure aren't very common.

So, in summary:

 

I wanted the 9.75" due to the towing I'm going to do. Not a lot and not really heavy, but 1000 miles each way to/from Lake Powell pulling the 23' SeaRay with 4 adults and a kid plus all the gear we'll need for a week on the lake. Already have one trip planned and expect several more, so wanted the strength that axle would give.

Yeah, I read about the Ohip meet before I bought my truck. Good info there, so appreciate your "work".

 

That is consistent with mine as well built 10/15. 3.5 EB, with 53A (regular) tow package. It has the 9.75 rear w/electronic lock. I don't know if it would have cost that much more just to get the Max tow package and be done with it.

 

My '15 3.5L EB spins the tires quite handily on dry pavement when towing nothing. This is with the 3.31 rear end. Kind of surprised at how easy it is to burn some rubber.

 

I was thinking about the spinning tires thing the other day. Had been driving my wife's AWD MLB GLK with its twin-turbo'd diesel and came to a stop at a light. Looked ahead and discovered that my lane was closed about 100' ahead. So, as the light was getting ready to change I left-foot braked and brought the R's up to just over 1000, bringing in the turbos. And when the light changed I nailed it and released the brake. I couldn't believe how fast that thing moved! I really don't think the other guy had started to move when we cleared the barrier. And all w/o spinning a wheel.

That got me to thinking about doing that in the truck. In 2wd I think I'd have been sitting there in a big smokeout. But, what about 4auto? I used it in a monsoon recently and saw it put some power to the front frequently as I came off of a stop. Anyone know if it reacts quickly enough to prevent just sitting there spinning the wheels?

 

I'm fairly certain it would. You'd probably see a bit of wheel slippage before the front end was fully locked in, but I don't think you'd notice.

 

May have to try that.

 

The order guide shows the 2.7 Payload Package 622 and HD Payload package 627 both include a 9.75 gearset, and are the only references to "9.75" in the guide.

2.7L V6 ECOBOOST® PAYLOAD PACKAGE (622)
Availability:
● Opt. on XL, XLT and Lariat
Not available with:
● 122” WB
● Class IV Trailer Hitch (53B) and Max Trailer Tow Package (53C)
Requires:
● 2.7L V6 EcoBoost® engine (99P)
● Trailer Tow Package (53A)
Includes:
● 3.73 Electronic-locking rear axle
● 9.75" gearset
● Mechanical Parking Brake

HEAVY-DUTY PAYLOAD PACKAGE (627)
Usage: Increases GVWR to 7600 lbs. on XL and 7850 lbs. on XLT and Lariat lbs. for
improved payload and towing
Availability:
● Opt. on XL, XLT Base, XLT Mid and Lariat Base
Not available with:
● 2.7L V6 EcoBoost® engine (99P)
● 122” WB on XL and XLT
● 145” WB on XL, XLT and Lariat
● XL/XLT Chrome Appearance Package (86A, 86B)
● XL/XLT Sport Appearance Package (861, 862)
Requires:
● Trailer Tow Package (53A) required when ordered with 5.0L Engine (99F)
● Max Trailer Tow Package (53C) required when ordered with 3.5L EcoBoost® Engine
(99G)
Includes:
● 3.73 Electronic-locking rear axle
● 9.75" gearset
● LT245/70R17E BSW all-terrain tires (A/T) (T7C) (XL only)
● LT275/65R18C OWL all-terrain tires (A/T) (T8C) (XLT and Lariat)
● Upgraded springs and auxiliary transmission oil cooler
● XL: 17" Silver Steel Heavy-Duty Payload Pkg. wheels (64W)
● XLT/Lariat: 18” Silver Aluminum Heavy-Duty Payload Pkg. wheels (64H)
Optional Equipment:
● XL: 18” Silver Aluminum Heavy-Duty Payload Pkg. wheels (64H) (LT275/65R18C OWL
all-terrain tires (A/T) (T8C) are included with the Unique 18” Aluminum wheels (64H))

 

It appears that the difference between the 9.75 and the 9.75 HD are that the 9.75HD comes in 3.73 and it holds more fluid. I see no mention of anything else being different.