NHTSA ID Number: 10201637
Manufacturer Communication Number: TSB 21-2330
Summary
Some 2020 Mustang
GT350 – 2020-2021 Mustang Mach 1/Shelby GT500 vehicles may exhibit a rear differential fluid leak at the differential cooler line fittings. This may be due to a seal within the fittings. To correct the condition, follow the service procedure to replace both rear differential cooler line fittings.
Model:
2020-2021 Mustang Mach 1
2020 Mustang Shelby GT350
2020-2021 Mustang Shelby GT500
Issue: Some 2020 Mustang Shelby GT350, 2020-2021 Mustang Mach 1/Shelby GT500 vehicles may exhibit a rear differential fluid leak at the differential cooler line fittings. This may be due to a seal within the fittings. To correct the condition, follow the service procedure to replace both rear differential cooler line fittings.
Action: Follow the Service Procedure steps to correct the condition on vehicles that meet the following criteria:
- One of the following vehicles:
- 2020 Mustang Shelby GT350
- 2020-2021 Mustang Mach 1
- 2020-2021 Mustang Shelby GT500
- Rear differential fluid Leak at the cooler line fittings located on the rear axle assembly
NOTE: Part quantity refers to the number of that service part number required, which may be different than the number of individual pieces. Service part numbers contain 1 piece unless otherwise stated. “As Needed” indicates the part is required but the number may vary or is not a whole number; parts can be billed out as non-whole numbers, including less than 1.
Parts
| Service Part Number | Quantity | Description | |
| MR3Z-6K741-A | 2 | Oil Cooler Adapter | Package Contains 1 Piece, 2 Pieces Required |
| XY-75W85-QL
Last update on 2026-06-18 / Affiliate links / Images from Amazon Product Advertising API | As Needed | Motorcraft® SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant | – |
XL-3
Genuine Ford Fluid XL-3 Friction Modifier Additive - 4 oz.
Last update on 2026-06-18 / Affiliate links / Images from Amazon Product Advertising API | As Needed | Motorcraft® Additive Friction Modifier | – |
Service Procedure
1. Disconnect the cooler lines from the rear axle housing. Refer to Workshop Manual (WSM), Section 205-02 Rear Drive Axle/Differential > Removal and Installation > Axle Assembly > Removal Steps 8-9. The differential fluid will drain out of the axle assembly during this step.
2. Remove and discard both fittings from the axle housing.
3. Install the new fittings. Tighten both fittings to 23 Nm (17 lb-ft).
4. Reinstall the cooler lines. Refer to WSM, Section 205-02 Rear Drive Axle/Differential > Removal and Installation > Axle Assembly > Installation Steps 4-6.
5. Refill the axle to the proper fill level. Refer to WSM Section 205-02 Rear Drive Axle/Differential > General Procedures > Differential Fluid Level Check.
2 Affected Products
Vehicle
1 Associated Document
Manufacturer Communications
21-2330
23 September 2021
- SATISFIES REQUIREMENTS - for gear oil viscosity of SAE 75W80, 75W, 80W and 85W, as well as SAE 30 and SAE 10W30 motor oil
- APPLICATIONS - include differential oil, final drive oil, gear oil and transfer case fluid, this product is not designed for use in most manual transmissions or transaxles with synchronizers, as extreme slipperiness may cause shifting problems
- CONTAINS - additional friction modifiers for suitability with clutch-type limited slip differentials - for most LSDs, no additional friction modifiers are required, known formerly as LightWeight Gear Oil
- POPULAR GEAR OIL FOR - in many late model BMW, Dodge, Ford, GM, Jeep, Lexus, Mercedes-Benz, Ram, Toyota, also popular in many Formula racing transaxles, including Hewland LD-200 and FTR sequential
- WHY RED LINE - Established in 1979, Red Line Products perform & protect better than any on the market. No compromises
- SATISFIES REQUIREMENTS - for gear oil viscosity of SAE 75W80, 75W, 80W and 85W, as well as SAE 30 and SAE 10W30 motor oil
- APPLICATIONS - include differential oil, final drive oil, gear oil and transfer case fluid, this product is not designed for use in most manual transmissions or transaxles with synchronizers, as extreme slipperiness may cause shifting problems
- CONTAINS - additional friction modifiers for suitability with clutch-type limited slip differentials - for most LSDs, no additional friction modifiers are required, known formerly as LightWeight Gear Oil
- POPULAR GEAR OIL FOR - in many late model BMW, Dodge, Ford, GM, Jeep, Lexus, Mercedes-Benz, Ram, Toyota, also popular in many Formula racing transaxles, including Hewland LD-200 and FTR sequential
- WHY RED LINE - Established in 1979, Red Line Products perform & protect better than any on the market. No compromises
- API GL-5 GEAR OIL FOR DRIVETRAINS: Designed for differentials, transfer cases, and gear systems in a wide range of U.S., European, and Asian vehicles
- OEM SPECIFIC FORMULATION: Delivers performance equal to or better than OEM fluids, ensuring smooth gear operation, frictional stability, and gear functionality while preventing shuddering, sticking, and slipping
- OUTSTANDING EXTREME PRESSURE (EP) PROTECTION: Exceptional shear stability and friction control for seamless gear transitions, torque transfer, and superb performance in high horsepower, high-speed, sustained mechanical and thermal loads
- ADVANCED METAL PROTECTION: Formulated to protect brass, copper, and aluminum alloys, outperforming many OEM and premium brands in severe service conditions
- ALL-CLIMATE PERFORMANCE: Superior performance in both extreme heat and cold, down to -50°F, and supports lifetime fill unless otherwise specified by the manufacturer
- SATISFIES REQUIREMENTS - for gear oil viscosity of SAE 75W80, 75W, 80W and 85W, as well as SAE 30 and SAE 10W30 motor oil
- APPLICATIONS - include differential oil, final drive oil, gear oil and transfer case fluid, this product is not designed for use in most manual transmissions or transaxles with synchronizers, as extreme slipperiness may cause shifting problems
- CONTAINS - additional friction modifiers for suitability with clutch-type limited slip differentials - for most LSDs, no additional friction modifiers are required, known formerly as LightWeight Gear Oil
- POPULAR GEAR OIL FOR - in many late model BMW, Dodge, Ford, GM, Jeep, Lexus, Mercedes-Benz, Ram, Toyota, also popular in many Formula racing transaxles, including Hewland LD-200 and FTR sequential
- WHY RED LINE - Established in 1979, Red Line Products perform & protect better than any on the market. No compromises
- FlexFill squeezable pouch releases 2X more fluid with less effort for 3X faster filling vs. traditional bottle packaging
- Contains limited slip for optimal performance of the clutch pack, while also delivering 30% better protection against towing and heavy loads and 1.5X better gear wear protection
- Advanced full synthetic helps prevent noise and reduce chattering, while protecting gear teeth from wearing out prematurely
- High and low temperature protection ranges from -50F to 300F degrees for cold temperature fluidity and high temperature performance
- Fights rust and corrosion with corrosion inhibitors and safeguards against impurities, oxidation and thermal breakdown
Last update on 2026-06-04 / Affiliate links / Images from Amazon Product Advertising API
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Warranty Status: Eligible under provisions of New Vehicle Limited Warranty (NVLW)/Service Part Warranty (SPW)/Special Service Part (SSP)/Extended Service Plan (ESP) coverage. Limits/policies/prior approvals are not altered by a TSB. NVLW/SPW/SSP/ESP coverage limits are determined by the identified causal part and verified using the OASIS part coverage tool. Labor Times Description Operation No. Time 2020 Mustang Shelby GT350, 2020-2021 Mustang Mach 1/Shelby GT500: Inspect And Replace The Cooler Line Fittings On The Rear Axle Includes Time To Check And Adjust Differential Fluid (Do Not Use With Any Other Labor Operations) 212330A 0.6 Hrs. Repair/Claim Coding Causal Part: 6K741 Condition Code: D8
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