Ford Falcon XK Rear Axle Troubleshooting and Minor Repairs Guide

The rear axle assembly in the Ford Falcon XK supports the axle shafts, differential gears and drive pinion within a single housing. The design allows the axle shafts, differential assembly and drive pinion components to be removed for servicing while the axle housing remains installed in the vehicle.

The axle shafts are supported by ball bearings at the outer ends of the axle housing, while the differential assembly is mounted on two opposed tapered roller bearings retained within the housing by removable bearing caps.

Differential bearing preload and drive gear backlash are adjusted by adjusting nuts located behind the differential bearing cups.

The drive pinion is mounted on two opposed tapered roller bearings, and the bearing preload is controlled by a collapsible spacer positioned between the front bearing cone and a shoulder on the pinion shaft. Proper gear tooth contact between the pinion and ring gear is achieved by adjusting shims located between the rear bearing cone and the pinion gear.

Understanding the basic construction of the axle assembly is essential when diagnosing rear axle noise or drive line vibration.

Rear Axle Trouble Symptoms and Possible Causes

Rear axle problems are usually identified by unusual noises, vibration, or excessive backlash in the drivetrain. Because similar symptoms can originate from other parts of the vehicle, it is important to determine whether the noise is actually coming from the axle assembly.

A road test is often required to properly diagnose rear axle issues.

Excessive Rear Axle Noise

Some gear noise from the rear axle is normal since the gears operate in constant mesh. However, excessive noise usually indicates the early stages of mechanical wear or incorrect adjustment.

Diagnosis Procedure

To determine whether the noise originates in the rear axle:

Check tyre pressures and verify the rear axle lubricant level is correct.
Drive the vehicle until the axle lubricant reaches normal operating temperature.
With the vehicle stopped and the transmission in neutral, run the engine at several speeds.

If the noise is still present during this test, it may originate from the engine or exhaust system rather than the axle.

If the noise occurs only while the vehicle is moving, it is likely related to the drivetrain.

Additional Checks

Drive the vehicle on different road surfaces during the test. Smooth asphalt or sealed roads will reduce tyre noise, making drivetrain noises easier to identify.

Tyre noise can sometimes be eliminated by cross-switching the tyres, while snow tyres may produce noises that conventional tyres do not.

A worn or damaged wheel bearing often produces the loudest noise when the vehicle is coasting at low speeds, and the sound typically disappears when the brakes are applied lightly.

To check for bearing problems, raise each wheel and rotate it by hand while checking for roughness or abnormal noise.

If external causes have been eliminated and the noise remains, road test the vehicle under several operating conditions including:

Drive
Cruise
Float
Coast

If noise persists during these conditions, the axle assembly should be removed and inspected.

Excessive Rear Axle Backlash

Excessive backlash within the axle assembly can result from wear or looseness in several drivetrain components.

Possible causes include:

Worn axle shaft splines
Loose axle shaft flange nuts
Loose universal joint flange mountings
Excessive backlash between the pinion and drive gear
Worn or improperly adjusted differential gears
Worn differential bearings

Correct diagnosis requires checking all drivetrain components before adjusting the differential assembly.

Drive Line Noise or Vibration

Driveline vibration or abnormal noise can result from several mechanical issues.

Common causes include:

Lack of lubrication in drivetrain components
Worn universal joint bearings
Missing or damaged driveshaft balance weights
Bent or damaged driveshaft
Excessive driveline angles
Undercoating or debris on the driveshaft affecting balance

Because driveshaft imbalance can easily create vibration, any undercoating material applied to the shaft should be inspected and removed if necessary.

Proper lubrication and regular inspection of universal joints and driveshaft components will prevent many of these issues.

Rear Axle Service Considerations

Before performing adjustments or repairs to the axle assembly, it is essential to confirm that the noise or vibration is not caused by:

Tyres
Engine operation
Transmission components
Exhaust system vibration

Accurate diagnosis ensures that unnecessary axle disassembly is avoided.

If internal axle components are suspected, the axle should be removed, disassembled and inspected for wear, incorrect adjustment or damage.

Safety, Copyright and Source Notice

Safety Disclaimer
Working on motor vehicles involves mechanical, electrical and chemical hazards. Always ensure the vehicle is safely supported, the engine is switched off when appropriate, and suitable safety equipment such as gloves and eye protection are used. If you are unsure about any repair or maintenance procedure, consult a qualified mechanic before attempting the work.

Source
Information compiled from period factory service literature.

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