Replace the rear differential pinion seal to stop fluid leaks from the front of the differential where the driveshaft connects.

Warnings

Tools required

Parts

• Rear differential pinion seal × 1 — Use OEM specification
• Pinion nut (reuse if not damaged) × 1 — Use OEM specification

Fluids

• Motorcraft 75W-140 Synthetic Gear Oil — 2 qt

Preparation

1. Park vehicle on level surface and apply parking brake firmly
2. Place wheel chocks behind front wheels
3. Raise rear of vehicle and support securely on jack stands at frame rails
4. Allow differential to cool to ambient temperature if recently driven
5. Clean area around pinion flange and driveshaft connection with brake cleaner

Procedure

1. 1

   Mark pinion position and measure preload
   Using the inch-pound torque wrench on the pinion nut, rotate the pinion several complete revolutions and measure the rotational torque required to keep it turning (pinion bearing preload). Record this value in inch-pounds. Use the paint marker to mark the exact relationship between the pinion shaft, pinion nut, and flange for reference during reassembly. Mark a line across all three components.
2. 2

   Remove driveshaft
   Remove the four U-joint strap bolts connecting the rear driveshaft to the pinion flange. Support the driveshaft and slide it rearward off the pinion flange. Do not allow the driveshaft to hang unsupported. Secure it to the frame or exhaust with wire or set it aside if clearance permits.
   Torque spec

   Driveshaft U-Joint Straps20 Nm (15 lb-ft)
3. 3

   Remove pinion flange nut
   Using the pinion flange holding tool to prevent rotation, remove the pinion nut with a 21mm socket. If reusing the nut, inspect threads carefully for damage. Count and record the number of exposed threads on the pinion shaft before nut removal to aid in reassembly to approximately the same position.
   ⚠The pinion flange will be under slight spring pressure from the pinion bearings. Control it as you remove the nut.
4. 4

   Remove pinion flange
   Using a suitable puller or by carefully tapping with a soft mallet, remove the pinion flange from the pinion shaft. The flange should slide off once the nut is removed. Note the orientation and any shims or washers behind the flange. Keep all components in order for reassembly.
5. 5

   Remove old pinion seal
   Using the seal puller or small pry bar, carefully remove the old pinion seal from the differential housing. Work around the perimeter evenly to avoid damaging the seal bore. Inspect the seal bore for scoring, burrs, or damage that could cause the new seal to leak.
   ⚠Be extremely careful not to scratch or gouge the seal bore surface in the housing. Any damage will cause the new seal to leak.
6. 6

   Prepare and install new seal
   Clean the seal bore thoroughly with brake cleaner and shop rags. Inspect the pinion flange sealing surface for grooves or wear; replace the flange if damaged. Lightly coat the outer diameter of the new seal with gear oil. Apply a thin coating of bearing grease to the seal lip. Using the seal installer or appropriately sized socket, drive the new seal squarely into the bore until it seats flush with the housing.
7. 7

   Reinstall pinion flange
   Lightly coat the pinion shaft splines with gear oil. Reinstall any shims or washers in their original positions. Slide the pinion flange onto the shaft, aligning it with the original marks. Install the pinion nut finger-tight, ensuring the threads engage properly.
8. 8

   Tighten pinion nut to restore preload
   Using the flange holding tool and torque wrench, gradually tighten the pinion nut while checking rotational torque frequently with the inch-pound torque wrench. Tighten until the alignment marks match AND the pinion bearing preload matches the original recorded value (typically 16-29 inch-pounds for used bearings). If marks align before reaching proper preload, continue tightening in small increments until preload is correct. Do not exceed 20 degrees past the original mark.
   ⚠️Never back off the pinion nut to reduce preload. If you overtighten, the pinion nut and crush sleeve must be replaced and the procedure restarted.
   ⚠Tighten in small increments and check frequently. Preload increases rapidly near the end of travel.
9. 9

   Reinstall driveshaft
   Guide the driveshaft forward onto the pinion flange, aligning the U-joint with the flange yoke. Install the U-joint strap bolts and tighten evenly in a cross pattern to the specified torque. Ensure the straps seat fully against the flange.
   Torque spec

   Driveshaft U-Joint Straps20 Nm (15 lb-ft)
10. 10

    Refill differential
    Locate the differential fill plug on the rear cover (passenger side, upper position). Remove the fill plug and add Motorcraft 75W-140 Synthetic Gear Oil until it begins to drip from the fill hole. The rear differential requires approximately 2.0 quarts. Reinstall and tighten the fill plug.

Reassembly

1. Verify all drain and fill plugs are tight and properly seated
2. Wipe down the differential housing to remove any spilled gear oil for easier leak detection
3. Lower vehicle from jack stands and remove wheel chocks

Verification

• Start engine and allow to idle, then shift through all gear ranges to circulate fluid
• Test drive vehicle for 10-15 minutes, including forward and reverse operation
• Re-check pinion nut torque after test drive to ensure it has not loosened
• Inspect pinion seal area for any signs of leakage with differential at operating temperature
• After 50-100 miles of driving, recheck seal area and differential fluid level

More procedures for this vehicle