Humming / High Pitch Sound From Drive Line – 2017-2021 Subaru

NHTSA ID Number: 10207215

Manufacturer Communication Number: 03-87-21


This bulletin provides a repair procedure for R152 type rear differentials.



This bulletin provides a repair procedure for R152 type rear differentials.  In some very rare cases, a customer may experience a humming / high pitch sound coming from the undercarriage while driving.  This can be caused by worn differential gear surfaces resulting from hard usage of the vehicle such as extreme weather conditions, severe road conditions, and / or steep incline driving.  A higher viscosity (thicker) gear oil has been introduced to provide additional protection against premature gear surface wear under these unusual driving conditions.



The higher viscosity fluid (75W-90) has been incorporated into production per the table below.

Model Starting VIN
Legacy M3019244
Outback M3197842
Impreza 4-Door M3606662
Impreza 5-Door M3714901
Crosstrek MH321913
Forester MH492693



REMINDER: Always order the most up-to-date replacement parts based on the specific VIN being repaired.

Part Description Part # Type R152 I.D. Numbers Differential Model # Reduction Ratios
38300AC380 43 VB1BAA 3.900(39/10)
38300AC390 44 VB1CAA 4.111(37/9)
38300AC440 E1 VB1AAC 3.700(37/10)


Part Description SOA Item # Description Package Size Warranty Part #
High Performance 75W90 SOA427V1700 Gear Oil Case of 12/1 qt. SOA635301 per qt.
SOA427V1710 16 Gallon Keg

NOTE: The Differential Mount Locking Nuts p.n. 023512000 are one-time use parts.  Refer to the applicable Service Manual and Electronic Parts Catalog (EPC) for the quantity requirements.




  • Customer satisfaction and retention starts with performing quality repairs.
  • Please read all the Steps outlined below before proceeding with any work.



Confirm the source of the sound is the rear differential and not from the wheel bearings and drive shafts before proceeding.  It is important to identify the rear differential type to verify applicability before proceeding with any service procedures.  The information below will outline how to identify the differential type.


STEP 1) Locate the identification number located on the rear differential.


(1)  LABEL







STEP 2) Compare the identification number with the part information chart provided on Page #1. Does the identification number match the part information shown?

YES: The rear differential is a R152 type.  Continue to STEP 3.

NO: The rear differential is NOT a R152 type.  Continue diagnosis as per the applicable Subaru Service Manual: Driveline/Axle > Symptoms and causes > INSPECTION.


STEP 3) Refer to the applicable Service Manual and review: General Description > Repair Contents > Action required before & after Battery Disconnect.  Additionally, record any stored seat position(s) before proceeding. Relearn any seat position memory after work is complete.  If the power rear gate (PRG) height has been customized, that position must also be noted and relearned.


STEP 4) IMPORTANT: The new rear differential MUST be filled with the new 75W90 gear oil. The service procedure for rear differential replacement remains unchanged.  Always refer to the applicable Service Manual and review the full requirements of the repair being performed. The Service Manual procedures contain information critical to performing an effective repair the first time, every time.  This includes but is not limited to important SAFETY precautions, proper inspection criteria, necessary special tools, required processes and related one-time-use parts needed for a complete and lasting repair. Refer to the applicable Subaru Service Manual: Driveline/Axle > DIFFERENTIALS > Rear Differential.



  • The Service Manual uses a black star (★) in the component breakdown illustrations to indicate  one-time use parts. For example, T1 and T2 are  self-locking nuts (023512000) and are one-time  use only. See the image to the right.
  • Whenever reconnecting the ground cable terminal to the battery sensor, torque to 7.5Nm  (5.5ft.-lbs. or 66 inch-lbs.) while supporting the  sensor with the other hand as outlined in the  applicable Service Manual under:



20 Affected Products




1 Associated Document

Manufacturer Communications

NUMBER: 03-87-21
DATE: 01/14/22

MC-10207215-0001.pdf 1143.453KB




SaleBestseller No. 1
Valvoline SynPower SAE 75W-90 Full Synthetic Gear Oil 1 QT
  • Formulated to maintain excellent low temperature fluid protection
  • Helps provide outstanding thermal stability for cleanliness and longer service life
  • Contains special additives to assist in protecting gear teeth from rust and corrosion and reduce chattering in limited-slip differentials
  • Recommended for conventional and limited slip differentials and non-synchronized manual transmissions where API GL-5 or API GL-4 fluid is specificed
Bestseller No. 2
Stens Lucas Oil 10047 SAE 75W-90 Synthetic Gear Oil/Transmission and Differential Lube - 1 Quart
  • Fit type: Vehicle Specific
  • Affordable solutions
  • Replaces OEM number: Lucas Oil: 10047
  • Excellent for use in limited-slip differentials
  • Packaging May Vary
SaleBestseller No. 3
Mobil 1 104361-UNIT 75W-90 Synthetic Gear Lube - 1 Quart
  • Mobil 1 Synthetic Gear Lube Ls 75W-90 Mobil 1 Synthetic Gear Lube Ls 75W-90 Is A Supreme Performance, Synthetic, Multi-Purpose, Sae 75W-90 Automotive Gear Lubricant Designed To Meet The Highest Level Of Performance Requirements Of Modern Passenger Vehicles In All Types Of Operating Conditions, Including Limited Slip Applications, As Well As Delivering Outstanding Power Transfer Performance
  • Compared To Conventional Hypoid Gear Lubricants, Mobil 1 Synthetic Gear Lube Ls 75W-90 Performs Exceptionally Well Over A Wide Range Of Temperatures
  • Through Creativity, Productivity And Innovation - This Brand Continues To Develop The Finest Automotive Accessories
  • Model Number : 104361-UNIT
SaleBestseller No. 4
Mobil1 1043611 Full Synthetic Gear Lubricant, 75W-90 Quart 6 PK
  • Mobil 1 Synthetic Gear Lube LS is a supreme performance, synthetic, multipurpose, automotive gear lubricant
  • Meet or exceed the highest level of performance requirements of many modern passenger vehicles – including limited slip applications
  • Helps protect against thermal and oxidative degradation, wear and corrosion, and viscosity loss associated with premature shearing
  • Promotes outstanding power transfer performance - even in some of the most severe driving conditions
  • Sold as 6 pack
SaleBestseller No. 5
Lucas Oil 10048 SAE 75W-90 Synthetic Transmission and Differential Lubricant - 1 Gallon
  • Fit Type: Vehicle Specific
  • Package Dimensions: 31.75 H x 15.24 L x 15.24 W (centimeters)
  • Country of Origin : United States
  • Package Weight: 3.447 kilograms
Bestseller No. 6
Ultra1Plus SAE 75W-90 Synthetic Gear Oil API GL-5 (Gallon - 4 QTS)
  • ✅ Extended gear and bearing life due to minimal deposits.
  • ✅ Longer seal Life.
  • ✅ Increased load-carrying capability.
  • ✅ Contribution to reduced maintenance cost and longer equipment life.
  • ✅ Helps to reduce operating costs.
Bestseller No. 7
StarFire Full Synthetic 75W90 Gear Lubricant 5 Gallon Pail
  • Provides excellent protection against wear under extreme pressure and high torque operation
  • High resistance to thermal breakdown
  • Helps prevent foaming, rust, and corrosion
  • Smooths and quiets operation
  • Protects against oxidative degradation
Bestseller No. 8
Royal Purple 01300 Max Gear Ultra-Tough High Performance Synthetic Gear Oil 75W-90-1 qt (Case of 2)
  • Brand: Royal Purple
  • LTDType: Synthetic
  • Viscosity: 75W-90
  • Volume: 1qt.
  • Mfgr. Warranty: No Warranty
Bestseller No. 9
Triax Synergy Gear MAX 75W-90 GL-5 Limited Slip, Ultra Long Drain 500k Miles, Manual Transmission, Gear/Differential Lubricant (1 Gallon)
  • EXTREME DRAIN INTERVALS - 500,000 miles for heavy duty trucks and passenger cars. 750,000 miles for Class 8 highway trucks.
  • PROFESSIONAL GRADE: Unrivaled shear stability and longevity. Meets and exceeds API GL-5 and Limited Slip requirements and a very wide range of specifications across multiple OEMs.
  • EXCELLENT WEAR CONTROL - Up to 62% less wear vs OEM Specifications across various standards. EXCEPTIONAL LOAD BEARING CAPACITY - Exceeds the highest load test rating, Stage 14.
  • WIDE RANGE OF APPLICATIONS - Hypoid and Ring Gears, Differentials, Limited Slip - Heavy Duty Highway, Passenger Cars, Heavy Duty Off-Road, Racing / Drifting. Will not shear under extreme torque. Features exceptional power transfer under extreme conditions. GREATLY EXCEEDS EP AND AW TESTS FZG AND L-37 - Proven protection far beyond spec requirements, delivers excellent EP (extreme pressure) and AW (anti-wear) performance in a wide range of LS and NON-LS gear systems, with hypoid and other gears.
  • TRUE SYNTHETIC WITH PAO - This is a true synthetic formulation with PAO base oil. Dont be fooled by cheap products which advertise themselves as Synthetics but have a VI Index below 160 and freeze at -30F and a very limited specification range.
SaleBestseller No. 10
Amsoil SVGPK 100% Synthetic Extreme Pressure (EP) SEVERE GEAR Lube, Quart Easy-Pack (75W-90)
  • Excellent for all cars and trucks, but especially well-suited for towing, hauling, racing, commercial use or other severe duty
  • Helps reduce operating temperatures
  • Resists breakdown from high heat, preventing acids and carbon/varnish formation
  • Excels in hot and cold temperature extremes

Last update on 2023-11-13 / Affiliate links / Images from Amazon Product Advertising API

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