How to check and refill differential fluid on a 1968 Ford Mustang GT Fastback (Bullitt)?

Owning a classic car like a 1968 Ford Mustang GT Fastback (Bullitt) comes with its own set of maintenance responsibilities. One common task is checking and refilling the differential fluid, which is crucial for keeping your rear differential in good working condition. Symptoms of low differential fluid include unusual noises like whining or grinding from the rear of the car, or even trouble with turning. Lack of maintenance in this area could lead to costly repairs, so it’s important to address this issue timely. Here is how to solve this issue:

Step 1: Gather Your Tools and Supplies

Before starting, make sure you have the following items:

• A socket set
• A car jack and jack stands or ramps
• A drain pan
• Differential fluid (consult your owner's manual for the correct type)
• A fluid pump or a bottle with a nozzle
• A clean rag

Step 2: Locate the Differential

First, find the differential. It is located at the middle of the rear axle of your Mustang. The rear differential typically looks like a large metal housing and is positioned between the two rear wheels.

Step 3: Jack Up the Car

Use a car jack to lift the rear of the vehicle. Securely position the car on jack stands or ramps for safety. Ensure the car is stable and won’t roll.

Step 4: Locate the Fill Plug

Find the fill plug on the differential housing. It is usually situated halfway up the differential, on the driver's side. The fill plug often looks like a bolt or a hex-head plug. Use your socket set to unscrew this plug.

Step 5: Check the Fluid Level

Insert a finger into the fill hole. The fluid level should be just below the fill hole. If you can’t feel the fluid with your finger, it’s low and needs to be refilled.

Step 6: Drain the Old Fluid (Optional but Recommended)

For a complete fluid change, locate the drain plug at the bottom of the differential. Place a drain pan beneath it and remove the plug using your socket set. Allow all the old fluid to drain out, then reinstall and tighten the drain plug.

Step 7: Refill the Differential

Using your fluid pump or the bottle nozzle, fill the differential with the appropriate type of fluid. Slowly add fluid until it just begins to dribble out of the fill hole. This ensures that the differential is properly filled to the correct level.

Step 8: Reinstall the Fill Plug

Replace and tighten the fill plug securely. Use a clean rag to wipe away any excess fluid that may have spilled around the fill hole.

Step 9: Lower the Car

Carefully remove the jack stands or ramps and lower the car back to the ground.

Step 10: Test Drive

Take the car for a short drive to circulate the new fluid and ensure everything is functioning properly. Listen for any unusual noises or changes in the car’s handling.

By following these steps, you ensure that your 1968 Ford Mustang GT Fastback’s differential remains in top condition, reducing the risk of mechanical issues and prolonging the life of your classic vehicle.