Yukon Gear Grizzly Locker / Ford 10.25in & 10.5in w/ 35 Splines

A Super Duty F-250 or F-350, an E-350 van or an Excursion with the Ford 10.25 or 10.5 inch rear axle (often called the Sterling) comes with either an open carrier or a Trac-Lok clutch limited slip. Both run out of answers when one rear tire is on ice, wet grass or a ledge with a load in the bed. The Yukon Grizzly Locker YGLF10.25-35 replaces that carrier with a full mechanical locker sized for the 10.25/10.5 ring gear and the 35-spline full-floating axle shafts these trucks use. There is no air pump, switch or wiring. It locks the two shafts together under power and lets the outside wheel overrun in a turn.

What the Grizzly Locker does in a Ford 10.25 or 10.5

The stock open carrier uses spider gears, so torque goes to whichever tire has the least grip. The Grizzly removes the spider gears and uses two driven clutch rings with face teeth that stay meshed while both wheels are driven. Both 35-spline shafts turn at the same speed, so the tire with traction does the work. When you turn and the outside wheel needs to run faster, its ring ratchets out of engagement and drops back in once the speeds match again. Yukon's description says the inner clutch teeth have a larger radius at the base, rated at up to 350 percent stronger than back-cut designs, with 8620 steel internals and US assembly. On a heavy truck that matters more than horsepower, because the shock loads come from towing, a loaded bed and spinning tires grabbing pavement again.

Symptoms that point to a locker swap

• One-tire spin backing a trailer up a wet ramp or pulling out of a soft lot, even with a working Trac-Lok
• Trac-Lok chatter or a clutch pack that no longer holds, leaving the truck acting open
• Broken spider gears or a worn cross shaft found with the cover off
• A planned gear change or bearing job where the carrier is already coming out
• Pinion or carrier bearing howl, the most common Sterling failure, which means the axle is getting opened anyway

How to confirm before ordering

Start with the axle tag on a cover bolt or the axle code on the door sticker, not the cover shape alone. The 10.25 and 10.5 both use a 12-bolt cover and 35-spline full-float shafts, and this one locker covers both ring gear sizes. Our Ford Sterling 10.25 and 10.5 problems guide shows how to tell them apart and how to separate bearing noise from gear noise. If you are still deciding between this and a selectable or a helical unit, read ELocker vs Grizzly and open vs limited slip vs locker.

Fitment

The listing and Yukon both state Ford 10.25 and 10.5 inch differentials with 35-spline axles. That family runs under F-250 and F-350 pickups from the mid-1980s on, E-series vans and the 2000-2005 Excursion. Years overlap and Ford changed the axle over time: the housing changed in 2008, 2011-and-later trucks use a different pinion, and some later F-250s got a Dana-built rear instead. Confirm the axle tag and spline count, or send us your year and VIN before ordering. For a smoother street unit that fits the same axles, compare the Detroit Truetrac for the 10.25/10.5 or the Dura Grip limited slip. More heavy axle parts are in our hard parts collection.

Install notes

• Pull the axle shafts (full floaters slide out after the hub flange bolts come out), mark the bearing caps and lift the carrier out.
• Move the ring gear onto the Grizzly case using new ring gear bolts and thread locker, torqued to Ford spec.
• Press on new carrier bearings. The Yukon 10.25/10.5 carrier installation kit has the bearings and races for this step.
• Reset carrier preload and backlash to Ford's procedure for your housing, then check the contact pattern. Our backlash and pinion depth guide explains the marks.
• If the pinion bearings are noisy, do them now with the 07-and-down 10.5 master overhaul kit instead of opening the axle twice.
• Fill with GL-5 75W-90 or 75W-140 gear oil. A mechanical locker has no clutch packs, so friction modifier is not needed for the locker.

Expect some clicking in tight, slow turns as the outside wheel ratchets. That is normal for an automatic locker and is usually mild on a long-wheelbase truck.

Does the YGLF10.25-35 fit both the Ford 10.25 and 10.5?

Yes. Yukon lists this one locker for both Ford 10.25 and 10.5 inch differentials with 35-spline axles. Confirm your axle tag and spline count, since later trucks changed axles.

Can I put it in my 2017 F-250?

Only if the truck has the Ford 10.5 rear. Some 2017-and-later F-250s have a Dana-built rear axle, which takes a different locker. Read the axle tag or send us your VIN first.

Do I need new gears to install it?

No. Your existing ring gear bolts onto the Grizzly case. Many owners regear at the same time because the carrier is already out, but it is not required.

Will it click or bang in parking lots?

An automatic mechanical locker can click or ratchet in tight, slow turns as the outside wheel overruns. It is normal. If you want silent operation, a helical Truetrac is the quieter choice.

What gear oil should I run with it?

Use GL-5 75W-90 or 75W-140. The Grizzly has no clutch packs, so friction modifier is not required for the locker.

What else should I replace while the carrier is out?

New carrier bearings and races at a minimum, plus new ring gear bolts and a cover gasket. If the pinion bearings are noisy, a master overhaul kit for your year of 10.5 saves opening the axle twice.