Section 05-00: Axle and Driveshaft—Service
1993 Mustang Workshop Manual
DIAGNOSIS

Noise Conditions

 

Non-Axle Noise

There are a few other conditions that can sound just like axle noise and have to be considered in pre-diagnosis.

The four most common are exhaust, tires, roof racks and trim mouldings.

  1. In certain conditions, the pitch of the exhaust may sound very much like gear whines. At other times, it can be mistaken for a wheel bearing rumble.
  1. Tires, especially snow tires, can have a high-pitched tread whine or roar, similar to gear noise. Radial tires, to some degree, have this characteristic. Also, any non-standard tire with an unusual tread construction may emit a roar or whine-type noise.
  1. Trim, grille and mouldings can also cause whistling or whining noise.

    Be sure that none of these are the cause of the noise before proceeding with an axle teardown and diagnosis.

 

Axle Noise

The following is a glossary of axle noise terms:

  1. Gear noise is the typical "howling" or "whining" of the ring gear and pinion due to an improper gear pattern, gear damage, or improper bearing preload. It can occur at various speeds and driving conditions, or it can be continuous.
  1. Chuckle is a particular "rattling" noise that sounds like a stick against the spokes of a spinning bicycle wheel. It occurs while decelerating from 64 km/h (40 mph) and can usually be heard all the way to a stop. The frequency varies with the speed of the vehicle.
  1. Knock is very similar to chuckle; though it may be louder and occurs on acceleration or deceleration. The teardown will disclose what has to be corrected.
  1. Clunk may be a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE, or it may occur when throttle is applied or released. It is caused by backlash somewhere in the driveline or loose suspension components; it is "felt" or heard in the axle.
  1. Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by malfunctioning pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds; this distinguishes it from gear whine, which usually comes and goes as speed changes.
  1. Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a malfunctioning wheel bearing. The lower pitch is because the wheel bearing turns at only about one-third of driveshaft speed. In addition, wheel bearing noise may be high-pitched, similar to gear noise but will be evident in all four driving modes.
  1. Chatter on corners is a condition where the whole rear end vibrates only when the vehicle is moving. The vibration is plainly felt as well as heard. In conventional axles, extra differential thrust washers cause a condition of partial lockup that creates this chatter. Chatter noise on Traction-Lok axles can usually be traced to erratic movement between adjacent clutch plates and can be corrected with a lubricant change.
  1. Click at engagement is a condition on axles of a slight noise, distinct from a "clunk," that happens in REVERSE or DRIVE engagement. It can be corrected by installing a slinger between the companion flange and front pinion bearing.
  1. Axle shaft noise is similar to gear noise and pinion bearing whine. However, axle shaft bearing noise will normally distinguish itself from gear noise by occurring in all driving modes (drive, coast and float), and will persist with transmission in NEUTRAL while vehicle is moving at concern speed. If upon ride evaluation, vehicle displays above noise condition, remove suspect axle shafts, replace wheel seals, and install a new set of axle shafts. Re-evaluate vehicle for noise before removing any internal components.

    To aid in isolating noises, refer to the following Diagnosis charts.

    CONDITION POSSIBLE SOURCE
    •Noise is the same in all modes Road noise
    •Tire noise
    •Front wheel bearing noise
    •Pinion bearings
    •Wheel bearings
    •Axle shaft surface finish
    •Noise changes with type of road Road noise
    •Tire noise
    •Noise tone lowers as vehicle speed is lowered Tire noise
    •Noise most pronounced on turns Differential side and pinion gears
    •Similar noise is produced with vehicle standing and driving Engine noise
    •Transmission noise
    •Noise is in one or more modes (Drive,
    Cruise, Coast, Float)    		 Ring and pinion gear
    •Clunk on acceleration or deceleration Worn differential cross shaft in case
    •Vibration Refer to Section 00-04

REAR AXLE DIAGNOSIS
ConditionPossible SourceAction
  • Excessive Rear Axle Noise
  • Differential carrier.
  • Road test vehicle to ensure concern is rear axle noise rather than other system noise. Refer to General Diagnostic Procedure. Service and replace parts as required.
  • Loud "Clunk" In Driveshaft When Shifting From REVERSE to DRIVE
  • Driveshaft.
  • Raise vehicle, rotate driveshaft by hand to isolate concern as a driveshaft or rear axle concern. Service as required.
 
  • Rear axle shafts or carrier.
  • Remove and inspect. Service as necessary.
  • Limited-Slip or Traction-Lok Axle Does Not Work in Snow, Mud or on Ice
  • Differential.
  • On Turns, The Rear Axle Has a High-Pitched Chattering Noise (Limited-Slip or Traction-Lok Axles Only). Slight Chatter Noise on Slow Turns After Extended Highway Driving is Considered Acceptable and Has No Detrimental Effect on the Locking Axle Function
  • Lubricant.
    Road test vehicle—drive vehicle in tight circles—5 clockwise and 5 counterclockwise. If chatter is still evident, flush and replace with Limited Slip Lubricant XY-90-QL or equivalent—plus 4 ounces of Friction Modifier C8AZ-19B546-A (EST-M2C118-A) or equivalent.
 
  • Differential.
  • Remove differential, service as required.