2021-2025 Audi Gearbox Noises/Vibrations TSB 2074857/1

Audi has released Technical Service Bulletin (TSB) 2074857/1 to address customer complaints of Audi gearbox noises vibrations when driving in tight bends. This bulletin, issued on August 30, 2024, applies to various Audi Q7, Q8, A8, and S8 models from 2021 to 2025. It explains the technical background of the issue and outlines a potential repair procedure involving the transfer box gear oil.

Symptoms

Owners of affected Audi vehicles may notice "Noises/vibrations in tight bends." These symptoms are typically reproducible by technicians and are significantly more noticeable compared to an identical comparison vehicle.

Understanding the Issue: The Torsen Differential

Audi's permanent all-wheel drive system, featuring the Torsen differential, provides superior driving dynamics. This system utilizes a self-locking center differential that generates its locking effect through worm gears. This design allows the axle with more traction to receive up to three times more torque than the other axle.

However, under specific conditions—such as significant speed differences between the front and rear axles in very tight bends, especially at high speeds—high friction forces can occur between the worm gear and the axial thrust washers in the differential. This can lead to a "stick-slip effect" where the surfaces contact each other, causing other vehicle components to resonate and generate a vibration or hum. Audi clarifies that "This issue is merely a comfort-related complaint. The specified behavior is construction-related. No damage occurs to components."

Factors Influencing the Condition

Several factors can negatively impact or exacerbate the Audi gearbox noises vibrations:

• Wheels: Differences in tread depth, hardness, width, or tire manufacturer (AO code), as well as the use of summer or winter wheels.
• Wheel Alignment: Additional tension in the drivetrain due to improper wheel alignment.
• Assembly Mountings: Possible noise transmission from assembly mountings.
• Loose or Incorrectly Installed Parts: Noise generation or increase due to loose parts, parts under tension, or incorrectly installed components in the vehicle's interior or chassis.

Repair Procedure: Transfer Box Gear Oil Change

An improvement in the noises/vibrations can often be achieved by changing the gear oil in the transfer box. This procedure replaces the friction modifier that may have degraded with increased mileage, which contributes to the stick-slip effect. The precise steps for this repair are detailed in the Workshop Manual.

For accurate evaluation and repair, the gearbox oil temperature must be between 40° C and 70° C (104° F and 158° F). A workshop tester should be used to determine the exact oil temperature. After the gear oil replacement, the issue should be significantly reduced within 125 miles of driving, depending on the driving profile. "The full effect of the oil change only becomes apparent after driving a distance of approx. 60 miles."

Warranty and Service Information

For vehicles still under warranty, claims must adhere to the Audi Warranty Policies and Procedures Manual. If the vehicle is outside of any warranty, this Technical Service Bulletin is informational only.

• Service Number: 3936
• Damage Code: 0020

Labor Operations:

Operation Description	Labor Code	Time Units (TU)
Remove and install rear transmission mount	3738 19xx	See SRT with associated operations
Replace gear oil	3990 5599	50 TU

Diagnostic Time:

Operation Description	Labor Code	Time Units (TU)
GFF	0150 0060	Labor according to diagnostic log
Charge battery	2706 8950	See SRT with associated operations
Extended road test after measure	0121 0199	According to punch time (Max 200 TU)

Claim Comment: As per TSB 2074857/1.

Important Owner Information

Owners should be aware that the noises and vibrations described in TSB 2074857/1 are considered a comfort issue and do not indicate damage to vehicle components. If your vehicle is experiencing these symptoms, a gear oil change in the transfer box may resolve the issue. Note that the full benefits of the oil change will become apparent only after driving approximately 60 miles following the service.

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Source: NHTSA ID: 10255866