Yukon Gear Master Overhaul Kit 2015+ Ford 8.8in Rear Diff

A 2015 or newer F-150 that hums from the rear at highway speed, or a late Mustang that whines on decel after a few hard launches, usually has pinion or carrier bearings on the way out. This Yukon Gear and Axle YK F8.8-D master overhaul kit is built for the updated rear axle Ford calls the Super 8.8, used under the F-150 and the Mustang from the 2015 model year on. It carries the Koyo bearings and races, seals and small parts to rebuild the center section. It is also the setup kit to have on the bench when you swap ring and pinion ratios.

What the master overhaul kit does in a Super 8.8

The Super 8.8 is not just the old 8.8 with a new cover. Ford gave it larger bearings, a longer pinion with a larger pinion nut, 34-spline axle shafts and a 12-bolt cover in place of the traditional 10-bolt. That is why the older kits for 2009-and-earlier axles will not work here. Inside, the layout is the same idea: the pinion turns on two tapered bearings held under preload, the carrier rides on two more, and shims set pinion depth, backlash and carrier preload. Once a bearing wears, the pinion moves under load and the gear pattern shifts, which produces the speed-related whine owners hear. This kit puts new Koyo bearings and races at all four positions, along with Yukon's seals and the small parts a gear setup needs.

Symptoms this kit fixes

• Whine or hum from the rear that rises and falls with road speed, louder on throttle or on coast
• Growl from the center of the axle that does not change in turns
• Gear oil leaking from the pinion seal onto the driveshaft flange
• A clunk on takeoff or when shifting between Drive and Reverse from worn pinion bearings
• Bearing flakes or fine metal on the cover magnet at a fluid change

How to confirm the noise first

Drive at the speed where the noise is loudest and note whether it changes on throttle, on coast or in a turn. A noise that changes when you turn is usually a wheel bearing, which is not part of this kit. A load-sensitive hum from the middle of the truck points to the pinion or carrier bearings. With the 12-bolt cover off, rock the pinion flange up and down to feel for play. Check backlash with a dial indicator and paint the gears to read the pattern before teardown. If the pattern looks good and backlash is in range, the gears can usually be reused with new bearings.

Fitment

This kit fits the 2015-and-later Ford 8.8-inch rear in the F-150 and the Mustang. It is the right kit when your axle has the 12-bolt cover. A 10-bolt-cover solid axle from 2014 or earlier takes the YK F8.8-A kit, and the 2006-and-later IRS 8.8 in Ford SUVs and cars uses a different kit. On the Mustang, which has independent rear suspension from 2015, the stub axle seals and needle bearings are sold separately and are not in this kit. Check the axle tag or send us your year and VIN if you are not certain. Related parts are on the hard parts page.

Install notes

• Mark the old pattern and measure backlash before you pull anything apart, so you have a baseline to return to.
• Press new races into the housing and new bearings onto the pinion and carrier. A carrier bearing puller set gets the old carrier bearings off without damaging the shims.
• Start with the original pinion depth shim and adjust from the gear pattern.
• Use a new crush sleeve and pinion nut and tighten in small steps while checking rotating torque. Backing off an over-crushed sleeve does not work; it has to be replaced.
• On a Mustang, order the IRS stub axle seals and needle bearings at the same time.
• Refill with the gear oil type and amount on your axle tag or in the owner's manual, and add friction modifier first if the axle has a limited slip.

Changing ratios at the same time? See the 2015-up F-150 8.8 3.73 gear set.

Will this kit fit my 2012 F-150?

No. It is for the 2015-and-later Super 8.8 with the 12-bolt cover. A 2014-and-earlier F-150 8.8 with the 10-bolt cover uses an earlier kit.

What bearings are in the kit?

The YK F8.8-D uses Koyo bearings and races, with Yukon seals and small parts.

Does it include the Mustang IRS stub axle seals?

No. The stub axle seals and needle bearings used on the Mustang independent rear are sold separately.

Do I need this kit if I am installing new gears?

Yes. New gears need new pinion and carrier bearings, shims and a crush sleeve for a proper setup, and this kit covers those parts.

Does it cover wheel bearings?

No. It covers the center section. If the noise changes when you turn, check the wheel bearings separately.