Here's a general outline of the process. Specific steps and torque specifications will vary depending on your exact rear differential (e.g., 7.5" or 8.8"). Always consult a repair manual specific to your vehicle's year and model for detailed instructions and torque values. Failure to follow proper procedures can lead to damage to the differential and potentially serious injury.
1. Preparation:
* Safety First: Jack up the vehicle securely on jack stands. Never work under a vehicle supported only by a jack. Disconnect the negative battery terminal. Wear safety glasses and gloves.
* Gather Tools and Materials: You'll need a variety of tools including jack stands, socket wrench set (metric), torque wrench, drain pan, funnel, new differential gasket (ensure it's the correct one for your model), RTV silicone sealant (appropriate for differential applications), brake cleaner, rags, possibly a differential bearing preload tool (depending on the extent of the repair), and a repair manual.
* Fluid Collection: Drain the differential fluid into the drain pan. Note the amount and condition of the fluid. This is crucial for later refilling.
2. Differential Removal (Partial or Complete):
* The complexity of this step depends on whether you only need to replace the cover gasket or if there's internal damage requiring a complete differential rebuild. For a *simple gasket replacement*, you'll likely only need to remove the differential cover.
* Removing the Cover: Loosen and remove the differential cover bolts. The cover may be stuck due to corrosion; use penetrating oil if needed and proceed carefully to avoid damaging the cover. Once loosened, carefully pry the cover off with a suitable tool (e.g., putty knife, flathead screwdriver, etc.). Be prepared for fluid leakage.
* Cleaning: Thoroughly clean the mating surfaces of both the cover and the differential housing with brake cleaner and rags. Remove all old gasket material completely.
3. Gasket Replacement:
* Applying Sealant (if required): Some gaskets require a bead of RTV silicone sealant. Apply the sealant according to the manufacturer's instructions on the new gasket. Too much sealant can cause problems.
* Installing the New Gasket: Carefully install the new gasket onto the differential housing, ensuring it's properly seated.
* Reinstalling the Cover: Carefully align the differential cover and install the bolts. Do not overtighten. Tighten the bolts in a crisscross pattern, following the torque specifications outlined in your repair manual.
4. Reassembly and Fluid Refill:
* Refilling: Once the cover is securely tightened, refill the differential with the correct type and amount of gear oil specified for your vehicle. Refer to your owner's manual or repair manual.
* Check Fluid Level: Check the fluid level using the differential's fill plug.
* Lower the Vehicle: Carefully lower the vehicle from the jack stands.
5. Post-Repair Inspection:
* Check for Leaks: After driving a short distance, inspect the differential for any leaks. If there are leaks, you'll need to re-check the gasket installation and tightening torque.
Important Considerations:
* Internal Damage: If the differential has internal damage (e.g., broken gears, worn bearings), a simple gasket replacement won't fix the problem. A complete rebuild or replacement of the differential may be necessary.
* Torque Specifications: Incorrect torque can damage the differential. Use a torque wrench and follow the manufacturer's specifications precisely.
* Repair Manual: A repair manual specific to your 1999 Ford Crown Victoria Police Interceptor is essential. It will provide detailed instructions, diagrams, torque specifications, and other critical information.
This is a simplified overview. This process is complex and potentially risky if not done correctly. If you are unsure about any step, seek professional help from a qualified mechanic. Improper repair could lead to serious damage to your vehicle or personal injury.
