205-02 Rear Drive Axle/Differential	2013 - 2014 MKZ
Diagnosis and Testing	Procedure revision date: 08/29/2012

Rear Drive Axle and Differential

Preliminary Inspection

Visually inspect the housing, seals, and pinion flange for obvious signs of mechanical damage.

If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step

If the cause is not visually evident, verify the symptom and REFER to Symptom Chart: NVH.

Symptom Chart(s)

Diagnostics in this manual assume a certain skill level and knowledge of Ford-specific diagnostic practices.
REFER to: Diagnostic Methods (100-00 General Information, Description and Operation).

Symptom Chart: NVH

Symptom Chart

Condition	Possible Sources	Actions
Axle howling or whine – front or rear axle	Axle lubricant low	CHECK the lubricant level. FILL the axle to specification.
	Axle housing damage	INSPECT the axle housing for damage. INSTALL a new axle housing if necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
	Damaged or worn differential and gear assembly	INSPECT the differential and gear assembly for damage. INSTALL a new axle assembly if necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Driveline clunk - loud clunk when shifting from REVERSE to DRIVE	Incorrect axle lubricant level	CHECK the lubricant level. FILL the axle to specification.
	Excessive backlash in the axle	CHECK for excessive axle backlash. INSPECT and INSTALL a new axle assembly as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Driveline clunk — occurs as the vehicle starts to move forward following a stop	Loose rear axle mount	CHECK for loose bolts. TIGHTEN to specifications. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
High pitched chattering – noise from the rear axle when the vehicle is turning	Incorrect or contaminated lubricant	CHECK the vehicle by driving in tight circles (5 clockwise, 5 counter clockwise). DRAIN and REFILL with the specified rear axle lubricant as necessary.
	Damaged or worn differential (differential side gears and pinion gears)	INSPECT and INSTALL a new axle assembly as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Grunting — normally associated with a shudder experienced during acceleration from a complete stop	Loose rear axle mount bolts or suspension fasteners	CHECK for loose bolts. TIGHTEN to specifications. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Howl – can occur at various speeds and driving conditions. Affected by acceleration and deceleration	Incorrect ring and pinion contact, incorrect bearing preload or gear damage	INSPECT and INSTALL a new axle assembly as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Chuckle – heard at coast/ deceleration. Also described as knock	Incorrect ring and pinion contact or damaged teeth on the coast side of the ring and pinion	INSPECT and INSTALL a new axle assembly as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Knock – noise occurs at various speeds. Not affected by acceleration or deceleration	Gear tooth damage to the driver side of the ring and pinion	INSPECT and INSTALL a new axle assembly as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Scraping noise – a continuous low pitched noise starting at low speed	Worn or damaged pinion bearings	INSPECT and INSTALL a new axle assembly as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
Driveline shudder – occurs during acceleration from a slow speed or stop	Rear drive axle assembly mispositioned	CHECK the axle mounts and the rear suspension for damage or wear. Repair as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
	Loose rear axle bolts	CHECK the rear axle for loose bolts. TIGHTEN the bolts as necessary. REFER to: Axle Assembly (205-02 Rear Drive Axle/Differential, Removal and Installation).
	Driveline angles out of specification	CHECK for correct driveline angles.

Analysis of Leakage

Clean up the leaking area enough to identify the exact source.

A plugged Rear Drive Unit (RDU) housing vent can cause excessive pinion seal lip wear due to internal pressure buildup.

Verify the RDU lubricant level is at least 3-5 mm (1/8-3/16) below the bottom of the fill hole.

Axle Vent

A plugged vent will cause excessive seal lip wear due to internal pressure buildup. If a leak occurs, check the vent. If the vent cannot be cleared, install a new vent.

Drive Pinion Seal

Leaks at the drive pinion seal originate from the following causes:

Damaged seal
Worn seal journal surface

Any damage to the seal bore (dings, dents, gouges or other imperfections) distorts the seal casing and allows leakage past the outer edge of the drive pinion seal.

The drive pinion seal can be torn, cut or gouged if it is not installed correctly. The spring that holds the drive pinion seal against the pinion flange may be knocked out and allow fluid to pass the lip.

Metal chips trapped at the sealing lip can cause oil leaks. These can cause a wear groove on the drive pinion flange and result in pinion seal wear.

When a seal leak occurs, install a new drive pinion seal and check the vent to make sure it is clean and free of foreign material.

A new drive pinion flange must be installed if any of these conditions exist.

Drive Pinion Nut

NOTICE: Install the drive pinion nut to the correct torque specifications or damage to the differential components may occur.

On some high-mileage vehicles, oil may leak through the threads of the drive pinion nut. This condition can be corrected by installing a new nut.

Differential Seals

NOTICE: When installing shafts, do not allow splines to contact seals during installation or damage to the seals may occur.

Halfshaft pilot bearing housing seals are susceptible to the same types of damage as drive pinion seals if incorrectly installed. The seal bore must be clean and the lip handled carefully to avoid cutting or tearing it. The seal journal surface must be free of nicks, gouges and rough surface texture.

For information on differential seals,
REFER to: Rear Halfshaft Seal (205-02 Rear Drive Axle/Differential, Removal and Installation).