Front Differential Assembly: Inspection

Repair or replace the differential gear in the following cases:

• The hypoid drive gear and drive pinion shaft tooth surface are damaged, excessively worn, or seized.
• The roller bearing on the drive pinion shaft has a worn or damaged roller path.
• There is damage, wear, or seizure of the differential bevel pinion, differential bevel gear, washer, pinion shaft, and straight pin.
• The differential case has worn or damaged sliding surfaces.
  Fig 1: Identifying Differential Gear

  Courtesy of SUBARU OF AMERICA, INC.

1. BEVEL PINION GEAR BACKLASH 

   Measure the backlash between bevel gear and pinion. If it is not within specifications, install a suitable washer to adjust it.

   NOTE: Be sure the pinion gear tooth contacts adjacent gear teeth during measurement.

   ST1 498247001 MAGNET BASE

   ST2 498247100 DIAL GAUGE

   1. Standard backlash: 0.13 - 0.18 mm (0.0051 - 0.0071 in) 
   Fig 2: Measuring Backlash Between Bevel Gear & Pinion

   Courtesy of SUBARU OF AMERICA, INC.
2. HYPOID GEAR BACKLASH 
   1. Insert the SUBARU genuine axle shaft into the left and right side retainer holes. (TURBO model)

      ST 38415AA000 AXLE SHAFT

   2. Set the ST1, ST2 and ST3. Insert the needle through transmission oil drain plug hole so that the needle comes in contact with the tooth surface at a right angle and check the backlash.

      ST1 498247001 MAGNET BASE

      ST2 498247100 DIAL GAUGE

      ST3 498255400 PLATE

      1. Backlash: 0.13 - 0.18 mm (0.0051 - 0.0071 in) 
      Fig 3: Inserting Needle Through Transmission Oil Drain Plug Hole

      Courtesy of SUBARU OF AMERICA, INC.
   NOTE: If the backlash is outside specified range, adjust it by turning the holder in right side case.
3. TOOTH CONTACT OF HYPOID GEAR 

   Check the tooth contact of hypoid gear as follows: Apply a uniform thin coat of red lead on both tooth surfaces of 3 or 4 teeth of the hypoid gear. Move the hypoid gear back and forth by turning the transmission main shaft until a definite contact pattern is developed on hypoid gear, and judge whether face contact is correct. If it is inaccurate, make adjustment. Refer to ADJUSTMENT  , Front Differential Assembly.

   • Tooth contact is correct.
     Fig 4: Checking Tooth Contact Of Hypoid Gear

     Courtesy of SUBARU OF AMERICA, INC.