Ford 8-Inch Differential Master Overhaul Kit, Timken Bearings

A Ford 8-inch third member that howls on the highway, rumbles when you lift off the throttle, or is coming apart for a new ratio needs a fresh set of bearings, a new crush sleeve and a correct setup. This Yukon YK F8-AG master overhaul kit is built for one specific version of that job: the Ford 8-inch rear under a Mustang, Falcon, Comet, Fairlane, Maverick, Pinto, Granada or similar car that is running an aftermarket positraction carrier with the larger 1.781 in carrier bearing journals. If your 8-inch still has the factory carrier, read the fitment section before you order, because the carrier bearings are different.

What a master overhaul kit does in a Ford 8-inch

The Ford 8-inch is a drop-out, removable-carrier rear: the ring gear, pinion and carrier all live in a cast center section that bolts into the front of the axle housing. The pinion rides on two tapered bearings and is held at a set preload by a collapsible crush sleeve and the pinion nut. The carrier rides on two more tapered bearings, and shims behind them set both carrier bearing preload and ring gear backlash. When any of those bearings pits or loses preload, the gear mesh moves and the gears start to sing. A master kit replaces every one of those wear and setup parts at once so the gear pattern you set on the bench stays put on the road.

According to Yukon, the YK F8-AG includes Timken carrier bearings and races, Timken inner and outer pinion bearings and races, a pinion seal, a complete shim kit, ring gear bolts, a pinion nut, a crush sleeve, thread locker, marking compound with a brush, and a gasket. Ring and pinion gears and the carrier itself are not included.

Symptoms this kit addresses

• Whine that rises and falls with road speed, not engine speed
• Noise that changes between acceleration and coast, a sign the pinion bearings have worn and preload is gone
• A constant growl or rumble that gets louder in turns, often a carrier bearing
• Pinion seal leaking gear oil onto the driveshaft yoke
• Clunk or slop when you check pinion play by hand at the yoke
• A new gear set going in: old bearings and a used crush sleeve should never be reused on a re-gear

How to confirm before you buy

Rule out tires, wheel bearings and the transmission first. Our guide to differential whine on acceleration vs deceleration shows how the noise pattern points to pinion bearings versus gear mesh, and carrier bearing noise symptoms covers the growl that changes in corners. With the driveshaft off, grab the pinion yoke and feel for up-and-down play. Then pull the drain plug or third member and look for metal on the magnet and bearing flakes in the oil.

Fitment

Yukon lists the YK F8-AG for the Ford 8-inch rear with LM102949 carrier bearings and LM102910 races, sized for 1.781 in carrier journals, and describes it as fitting the 8-inch with an aftermarket positraction. Its chart covers cars such as the 1964-1973 Mustang, 1962-1967 Fairlane, 1964-1970 Falcon, 1970-1977 Maverick, 1971-1980 Pinto, 1975-1978 Granada, 1967-1970 Cougar, Comet and Capri, plus 1969-1974 E-100 vans, when that larger-journal carrier is installed. Most factory 8-inch carriers use the smaller 1.625 in journal and need a kit with LM501349 bearings instead, such as our Motive Gear RA310RMKT Ford 8-inch kit. Measure the carrier journal or read the number on your old carrier bearing before ordering. The Excel XL-1014-1 large-carrier kit is the other option we stock for the same 1.781 in setup. If you are unsure, send us the bearing number and we will confirm before it ships. More kits are on the rebuild kits page.

Install notes

• Press the old carrier bearings off with a proper puller such as the OTC 4520 side bearing puller set so the journals are not gouged.
• Set pinion depth first with the supplied shims, using a depth tool like the Proform pinion depth tool or by reading the marking compound pattern.
• Install the new crush sleeve and tighten the pinion nut in small steps, checking rotating torque with an inch-pound torque wrench. If you overshoot, a new sleeve is the fix; backing the nut off does not restore it. Our page on crush sleeve vs solid spacer explains why.
• Shim the carrier for preload and backlash, check backlash with a dial indicator, and torque the ring gear bolts with thread locker.
• Paint the gears, roll them both ways, and read drive and coast patterns before the center section goes back in.
• Fill with GL-5 hypoid gear oil of the grade your manual calls for, plus any friction modifier your posi carrier maker requires, and recheck after a short break-in drive.

Does the YK F8-AG fit a stock Ford 8-inch carrier?

Usually not. Yukon sizes this kit for 1.781 in carrier journals with LM102949/LM102910 carrier bearings, the size used by aftermarket positraction carriers. Most factory 8-inch carriers have 1.625 in journals that take LM501349 bearings, so check your old bearing number or measure the journal first.

Are the ring and pinion gears included?

No. The kit covers carrier and pinion bearings and races, pinion seal, shims, ring gear bolts, pinion nut, crush sleeve, thread locker, marking compound with brush and a gasket. Gears and the carrier are separate purchases.

What bearing brand is in this kit?

Yukon specifies Timken for the carrier and pinion bearings and races.

Can I reuse my old crush sleeve?

No. A crush sleeve deforms once to set pinion preload. Reusing it, or loosening the nut after over-tightening, leaves the pinion without proper preload and the gears will start to whine. Use the new sleeve in the kit.

What gear oil should go in after the rebuild?

A GL-5 hypoid gear oil in the viscosity your shop manual specifies. Many aftermarket clutch-type posi carriers also need a friction modifier, so follow the carrier maker's instructions.

Does it fix a whine from new gears that were set up wrong?

Only if you redo the setup. The kit gives you fresh bearings, shims and a new crush sleeve so you can reset pinion depth, preload and backlash; the noise goes away when the pattern is right.