Yukon Gear Grizzly Locker For Ford 9in w/ 31 Spline Axles

The Ford 9-inch went under 1957-1986 F-100 and F-150 pickups, 1966-1983 Broncos, early Mustangs, Fairlanes, Torinos and Thunderbirds, and it lives on in aftermarket housings under drag cars, street rods and rock buggies. Plenty of those axles came with 31-spline shafts or have been upgraded to them. If yours still has an open carrier or a tired Traction-Lok and you want both tires pulling every time, the Yukon Grizzly Locker YGLF9-31 is a full-time mechanical locker built for a Ford 9-inch with 31-spline axles.

What the Grizzly Locker does in a Ford 9-inch

A Grizzly Locker replaces the spider gears with a set of toothed couplers that keep both axles locked together under power. Yukon describes it as delivering 100 percent of the power to both tires, while still letting the outside wheel unlock and overrun in a turn so the truck can steer. There is nothing to switch on and no air or wiring. Yukon's design uses a larger radius at the base of the inner clutch teeth, which it rates at up to 350 percent stronger than back-cut designs, and 8620 steel internals. The Ford 9-inch makes this an easy install, because the carrier lives in a drop-out third member that comes out of the housing as one assembly and can be set up on a bench.

Symptoms that bring buyers to a locker

• One tire spinning on the starting line or on a ledge while the other sits still
• A worn clutch-type posi that slips under big horsepower or chatters in turns
• Broken spider gears or a cracked open case from shock loads on the trail
• Upgrading the axle to 31-spline shafts and needing a carrier to match

Expect the trade-offs of any full-time locker: a click or ratchet sound when the outer wheel unlocks in turns, some tire scrub in tight parking lot moves, and a tendency to push straight in slick corners. Read ELocker vs Grizzly Locker differences and open vs limited slip vs locker if you are still choosing.

How to confirm before you order

Pull an axle and count the splines; factory 9-inch shafts came in 28 and 31 spline, and aftermarket axles also come in 35 and 40. This unit is 31 spline only. Then check the third member. Factory centers used two carrier bearing sizes, 3.0625 in. and 3.250 in., and Ford 9 overhaul kits are sold by bearing number, so note which bearing your center section takes before you order bearings. If the center has a cracked pinion support or worn races, our Ford 9-inch problems and rebuild cost guide explains what to inspect.

Fitment

From the listing and Yukon's product page: Ford 9-inch, 31-spline axles, part number YGLF9-31. Because 9-inch axles were used in so many Ford cars and trucks and are widely swapped, there is no single vehicle list; match the axle and spline count, or send us the year and VIN and we will help. Running 35-spline shafts? Order the Grizzly Locker for Ford 9-inch 35-spline. Prefer to stay open? The Yukon Ford 9 open carrier is listed too. Browse hard parts for the rest of the axle.

Install notes

• Since the carrier comes out with the third member, rebuild the center while it is on the bench. The Yukon Ford 9 master overhaul kit (LM102910 bearings) and the USA Standard kit (LM501310 bearings) cover the two common bearing sizes.
• If you are changing ratio at the same time, a set like the Yukon Ford 9 3.50 gear set goes on the new locker; check backlash and pattern with our backlash and pinion depth guide.
• A locker multiplies the load on the shafts. If yours are original 28-spline or worn, a Yukon 1541H alloy Ford 9 axle is the usual upgrade; measure length and bearing size first.
• Use new ring gear bolts with thread locker and torque them evenly. Fill with conventional 75W-90 or 85W-140 gear oil. A locker has no clutch packs, so it does not need limited slip additive, then follow our break-in procedure if the gears are new.

Does this fit a Ford 8.8 or a 9.75?

No. It is built only for the Ford 9-inch drop-out center section. The 8.8 and 9.75 are different axles with their own lockers.

Is it a selectable locker?

No. It is a full-time automatic mechanical locker. Both axles are locked under power, and the outside wheel unlocks in turns. There is no switch, air line or wiring.

Can I drive it on the street every day?

Many people do. Expect a ratcheting click in turns, some tire scrub in tight maneuvers and more care on wet or icy corners than with an open or limited slip axle.

My axles are 28 spline. Will it work?

Not without new shafts. This is the 31-spline unit. You can either buy 31-spline axles or find a 28-spline locker.

Do I need special gear oil?

No limited slip additive is needed because there are no clutch packs. Use a quality 75W-90 or 85W-140 gear oil.