Sterling 10.50 Inch Rear Differential Service

How to Replace the Differential Fluid in a Sterling/Ford 10.50" Rear Axle

The Sterling 10.50 inch is a heavy duty, full floating rear differential manufactured by Ford Motor Company. The axle assembly has been used in the Ford Super Duty (F-250/F-350) since 1999, superseding the largely similar 10.25 inch differential used in previous 3/4 and 1 ton F-Series models. Its name is derived from the ring gear size (10.50 inches) and the plant at which it is manufactured (Ford's Sterling Axle Plant in Sterling, Michigan).

Applicable model years: 1999 - current Ford Super Duty
Sterling 10.50 differential gasket: Dana Spicer RD51999
Friction modifier (limited slip differentials): Motorcraft XL-3
Sterling 10.50 gear oil spec: 75W-140 full synthetic (recommend Amsoil Severe Gear 75W-140)

Sterling 10.50 in Axle Specs


Ford Motor Company

Production Plant:

Sterling Axle Plant, Sterling, Michigan


1999 - current Ford Super Duty


Full floating rear differential

Ring Gear Diameter:


Pinion Shaft Spline:

31 spline

Axle Tube Diameter:


Axle Shaft Diameter:


Axle Shaft Spline:

35 spline

Fluid Spec:

SAE 75W-140 synthetic gear oil
A friction modifier may be required for limited slip differentials

Fluid Capacity:

3.25 - 3.50 quarts, always add fluid to fill plug level

Service Intervals:

1999 - 2007

100,000 miles (normal conditions)
30,000 miles (severe service conditions, i.e. towing)


100,000 miles (normal conditions)
50,000 miles (severe service conditions, i.e. towing)

Differential Cover Bolt Torque:

29 - 39 ft-lbs

Sterling 10.50 Differential Fluid Replacement Procedures

Ford recommends replacing the differential oil at 100,000 miles under normal driving conditions, 30,000 miles for 1999 - 2007 model year trucks meeting severe service criteria, and 50,000 miles for 2008 and newer model year trucks meeting severe service criteria. Differential fluid should be replaced immediately if an axle is submerged in water as infiltration is highly likely.

Click any thumbnail to view fullsize, detailed image

10.50 rear differential

• Ensure the transmission is set to Park (or in-gear on manual transmissions) and that the parking brake is fully engaged.

• Lower and remove the spare tire and set aside.

Sterling 10.50 oil fill plug location

• Locate and loosen the fill plug using a 3/8" square drive. It is located on the driver side of the differential housing near the input shaft. The fill plug does not need to be removed at this time, however making sure that the fill plug is not seized before draining the fluid is a good practice.

Draining differential oil

• Place a suitable drain pan below the differential housing.

• Loosen (2) of the top differential cover bolts halfway, but don't remove them. Remove the remaining (10) bolts using a 1/2" socket.

• Carefully pry the differential housing cover using a razor knife, gasket scraper, putty knife, or thin flathead screwdriver until the silicon seal is broken and the oil begins to drain. Be cautious not to bend/damage the differential cover. The (2) top bolts left in place will keep the cover from splashing into the oil drain container.


Differential cover removed

• Allow the majority of the differential oil to drain, then remove the remaining differential cover bolts followed by the cover itself.

Cleaned differential cover

• Thoroughly clean the differential cover. All remnants of gasket material, silicon, oil, debris, and contaminants must be removed before it can be reinstalled.

Cleaning differential housing

• Wrap the differential carrier and ring gear assembly with a large plastic garbage bag.

• Thoroughly clean the differential housing sealing surface. All remnants of gasket material, silicon, oil, debris, dirt, and contaminants must be removed before the cover can be reinstalled. Use brake cleaner or a similar solvent on a clean, lint free rag to remove residual oil from the mounting surface and ensure a positive seal when the cover is reinstalled.

Silicon applied to differential cover

• Run a moderately sized bead (~1/4") of RTV silicon around the sealing surface of the differential cover (recommend Permatex 82180).

Note - a gasket may be used but is not required for this application. 10.50" differentials do not come factory installed with a gasket and only use silicon. We recommend using a gasket. If using a gasket, carefully install it onto the differential cover and, if desired, apply a light bead of silicon on the second side.

Differential cover installed

• Carefully reinstall the differential cover and all (12) bolts. Snug bolts down in a star or criss-cross pattern. Torque differential cover bolts to 29 to 39 lb-ft.

• Allow the differential cover sealant to cure per the manufacturer's specifications (generally 24 hours).

Oil seeping from fill plug

• Remove the fill plug and use a hand pump to add gear oil to the differential housing until it reaches the fill plug level. When the level is full, oil will begin to run out of the fill plug. Do not rely on the listed oil capacity; always add gear oil until it begins to run out of the fill plug.

Note - Limited slip differentials may require a friction modifier; use Ford/Motorcraft XL-3 (8 oz).

• Reinstall the fill plug and tighten snug.

• Drive vehicle so that the differential fluid reaches operating temperature, then park and check for leaks.