* Incorrect Seal Installation: While seemingly obvious, the most common cause is improper seal installation. Even a slight misalignment or damage to the seal during fitting can lead to leaks. The seal might not be seated properly in its groove, or the axle shaft itself might be damaged, preventing a proper seal.
* Damaged Axle Shaft: Scratches, pitting, or other damage to the axle shaft surface where the seal contacts can prevent a good seal, even with a new seal. The old seal may have masked the damage, which becomes apparent after replacement.
* Damaged Axle Housing: Similar to the axle shaft, damage to the axle housing where the seal seats can compromise the seal's effectiveness. This could be from previous damage or from improper installation force during seal replacement.
* Wrong Seal: It's possible the wrong seal was used during the repair. Different F-150 models and axle types might require different seals. Double-check the part number against the vehicle's specifications.
* Over-tightening: Excessive tightening of the axle nut or retaining components can deform the axle housing or crush the seal, leading to leakage.
* Loose or Damaged Retaining Ring: The seal might be held in place by a retaining ring. If this ring is loose, damaged, or improperly seated, it can prevent the seal from working correctly.
* Contamination: Dirt, debris, or old sealant residue inside the axle housing can prevent the seal from making proper contact. Thorough cleaning of the housing is essential before installing new seals.
* Leaking from elsewhere: The leak might not actually be coming *from* the seal itself, but from a different source, like a damaged axle tube, a cracked differential cover, or even a breather vent hose.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine the area around the replaced seals. Look for any signs of fluid leakage, paying close attention to the source of the leak. Sometimes a small pinhole leak in an axle tube can appear to be from the seal.
2. Pressure Test: A pressure test of the axle housing can help pinpoint the source of the leak.
3. Re-inspection of Seal Installation: Carefully check the seal installation again, ensuring it's seated properly and not damaged.
4. Check for Axle Shaft and Housing Damage: Inspect the axle shaft and housing for any damage that might be preventing a proper seal. This often requires removal of the axle shaft.
5. Verify Correct Seal Part Number: Ensure that the correct seal part number was used for the specific axle and year of the F-150.
If the problem persists after thorough inspection and re-installation, it is best to seek professional help from a qualified mechanic specializing in automotive repairs. Continuing to drive with an axle fluid leak can lead to serious damage to the axle components.
