Audi Audi A8 2018-present Drivetrain Bolt Torque Specifications & Fastener Values
Audi Audi A8 2018-present

Audi Audi A8 2018-present Drivetrain Bolt Torque Specifications

Comprehensive guide to drivetrain bolt torque specifications for the 2018-Present Audi A8 (D5) generation, covering various components.

Updated

Important Information

Safety guidelines and reference information for proper torque application

Quick Reference Guide
ft-lbs → Nm
× 1.356
ft-lbs → kg-m
× 0.138
Nm → ft-lbs
× 0.738
in-lbs → ft-lbs
× 0.083

Common Torque Patterns

Star Pattern

Used for wheels and other circular bolt patterns

Star Pattern torque pattern diagram showing proper bolt tightening sequence
Cross Pattern

Used for gaskets and cover plates

Cross Pattern torque pattern diagram showing proper bolt tightening sequence
Sequential Pattern

Used for head bolts and other critical components

Sequential Pattern torque pattern diagram showing proper bolt tightening sequence

Common Mistakes to Avoid

Over-tightening

Exceeding the specified torque value can stretch or break fasteners, damage threads, or crack components.

Prevention:

Always use a calibrated torque wrench and follow specifications exactly.

Incorrect Torque Sequence

Tightening bolts in the wrong order can cause uneven pressure distribution and potential leaks or damage.

Prevention:

Follow the manufacturer's specified torque sequence pattern.

Dirty Threads

Dirt, rust, or old thread locker can affect torque readings and proper fastener tension.

Prevention:

Clean and inspect all threads before assembly. Use new thread locker if specified.

Reusing TTY Bolts

Torque-to-yield bolts are designed to stretch and must not be reused.

Prevention:

Always replace TTY bolts with new ones. They are single-use only.

Dry vs. Lubricated

Not accounting for whether torque specs are for dry or lubricated fasteners can lead to incorrect tension.

Prevention:

Check if specs are for dry or lubricated threads. Use specified lubricant when required.

Recommended Tools

Torque Wrench (1/4" Drive)

Range: 2-25 ft-lbs
Small fasteners, delicate components

Torque Wrench (3/8" Drive)

Range: 10-100 ft-lbs
Most common automotive fasteners

Torque Wrench (1/2" Drive)

Range: 30-250 ft-lbs
Large fasteners, wheels

Angle Gauge

Torque-to-yield (TTY) bolts

Torque Wrench Care

  • Calibrate annually or after 5,000 clicks
  • Store at lowest setting
  • Keep clean and lubricated

Search Specifications

Search by component name, bolt size, or description

Torque Calculator

Convert between different torque units

Transmission

Torque specifications for the 8-speed automatic transmission and its related components. This includes mounting bolts, fluid drain/fill plugs, and internal components like the mechatronics unit.

1

Transmission Mounting Bolts

M12 x 1.75
Important Notes
Secures the transmission to the vehicle's frame. Critical for supporting the weight and preventing movement. Failure can cause drivetrain issues.
2

Transmission Fluid Drain Plug

M18 x 1.5
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Seals the transmission fluid pan and prevents leaks. Proper torque ensures the seal is maintained.
3

Transmission Fluid Pan Bolts

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Secures the transmission fluid pan to the transmission housing. Overtightening could damage the pan or gasket.
4

Mechatronics Unit Bolts

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
These bolts secure the mechatronics unit to the transmission body. These are critical for proper transmission operation. Estimated value based on similar VAG group components.
5

Transmission Oil Cooler Line Banjo Bolts

M12 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Connects the transmission oil cooler lines to the transmission housing. Proper torque is essential to prevent fluid leaks.

Transfer Case

Torque specifications for the transfer case and its related components. This includes mounting bolts, fluid plugs, and propeller shaft flange connections.

1

Transfer Case Mounting Bolts

M12 x 1.75
Important Notes
Securely fastens the transfer case to the transmission. Critical for transmitting power to the front and rear differentials.
2

Transfer Case Fill Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Provides access for checking and filling fluid in the transfer case. Must be correctly torqued to prevent leaks.
3

Transfer Case Drain Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Allows for draining of the transfer case oil. Proper torque ensures sealing and prevents fluid leakage.
4

Propeller Shaft Flange Bolts (Transfer Case Side)

M10 x 1.5
Important Notes
Securely connects the propeller shaft to the transfer case output flange. Critical for the reliable transfer of power.

Propeller Shaft

Torque specifications for the propeller shaft, also known as the driveshaft. This includes flange bolts, center support bearing bolts, and flex disc bolts.

1

Propeller Shaft Flange Bolts (Front Differential Side)

M10 x 1.5
Important Notes
Connects the propeller shaft to the front differential input flange. Proper torque is essential for vibration-free and safe operation.
2

Propeller Shaft Center Support Bearing Bolts

M8 x 1.25
Torque Value
20 ft-lbs (27 N·m)
Important Notes
Secures the center support bearing to the chassis. Provides crucial support to the center of the driveshaft and helps prevent vibration. Estimated value based on industry standard.
3

Flex Disc Bolts

M12 x 1.5
Important Notes
Connect the propeller shaft to other components. Correct torque ensures secure fastening and long life.

Front Differential

Torque specifications for the front differential and its related components. This includes mounting bolts, fluid plugs, and axle shaft flange connections.

1

Front Differential Mounting Bolts

M12 x 1.75
Important Notes
Mounts the differential to the vehicle's subframe. Supports and secures the differential, essential for proper function.
2

Front Differential Fluid Drain Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Ensures that the fluid stays in the differential and can be changed out periodically.
3

Front Differential Fill Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Ensures the fill port is sealed and that fluid doesn't leak from the differential.
4

Front Axle Shaft Flange Bolts (Differential Side)

M10 x 1.5
Torque Value
40 ft-lbs (55 N·m)
Important Notes
Attaches the front axle shafts to the differential's output flanges. Critical for transmitting power to the front wheels. **Critical Fastener**

Rear Differential

Torque specifications for the rear differential and its related components. This includes mounting bolts, fluid plugs, and axle shaft flange connections.

1

Rear Differential Mounting Bolts

M12 x 1.75
Important Notes
Securely attaches the rear differential to the vehicle's subframe. Supports and secures the differential, essential for proper function.
2

Rear Differential Fluid Drain Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Provides a seal for the differential oil and prevents leaks, and allows for scheduled oil changes.
3

Rear Differential Fill Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Provides a seal to the fill port and prevents leaks after fluid fill.
4

Rear Axle Shaft Flange Bolts (Differential Side)

M10 x 1.5
Torque Value
40 ft-lbs (55 N·m)
Important Notes
Attaches the rear axle shafts to the differential's output flanges. Critical for transmitting power to the rear wheels. **Critical Fastener**
5

Rear Axle Stub Shaft Bolt

M14 x 1.5
Important Notes
Fastens the axle stub to the wheel hub. This is a critical fastener. **Critical Fastener**

Wheel Hubs Axles

Torque specifications for wheel hub and axle components. This includes hub assembly bolts and axle nuts.

1

Wheel Bearing Hub Assembly Bolts

M12 x 1.75
Important Notes
Securely attaches the wheel hub and bearing assembly to the knuckle. Critical for wheel alignment and smooth rotation. **Critical Fastener**
2

Axle Nut (Center Locking Nut)

M24 x 1.5
Important Notes
Secures the axle shaft into the wheel hub, bearing. Extremely critical fastener. One-time use nut, replace after removing. **Critical Fastener**

Troubleshooting Guide

Common issues, diagnostic steps, and prevention guidelines

Common Issues

Bolt stretching, stripped threads, uneven torque patterns

Loose Components

Symptoms:
  • Rattling or vibration noises
  • Visible movement in components
  • Uneven panel gaps
Solutions:
  • Clean threads and mounting surfaces
  • Replace damaged fasteners
  • Apply proper torque in sequence
  • Use thread locker if specified

Stripped Fasteners

Symptoms:
  • Unable to achieve proper torque
  • Fastener spins freely
  • Visible thread damage
Solutions:
  • Use thread repair kit if appropriate
  • Install thread insert (HeliCoil)
  • Replace component if threaded hole is damaged
  • Upgrade to higher grade fastener if recommended

Overtightened Components

Symptoms:
  • Cracked or deformed parts
  • Broken fasteners
  • Compressed gaskets or seals
Solutions:
  • Replace damaged components
  • Use new fasteners
  • Follow proper torque sequence
  • Verify correct torque specifications

Diagnostic Steps

Visual inspection, torque verification, thread assessment

1

Visual Inspection

Inspect the affected area for any visible signs of damage or wear

  • Check for cracks or deformation
  • Look for signs of excessive wear
  • Verify proper fastener installation
2

Torque Verification

Verify the torque applied to the fasteners

  • Check the torque wrench calibration
  • Verify the torque specification
  • Compare the applied torque to the specification
3

Thread Assessment

Assess the condition of the threads

  • Check for signs of thread damage
  • Verify the thread type and size
  • Check for proper thread engagement

Prevention Guidelines

Best practices, maintenance tips, tool care

Best Practices

  • Always follow the recommended torque specification
  • Use the correct type and size of fasteners
  • Verify the torque wrench calibration regularly

Maintenance Tips

  • Regularly inspect the affected area for signs of wear or damage
  • Replace damaged or worn-out components promptly
  • Keep the work area clean and organized

Tool Care

  • Regularly clean and maintain the torque wrench
  • Store the torque wrench in a dry and secure location
  • Verify the torque wrench calibration before each use

Frequently Asked Questions

Find answers to common questions about torque specifications

Q1

Why are precise torque specifications important for drivetrain bolts?

Precise torque is crucial for drivetrain bolts to ensure proper clamping force, preventing loosening from vibration and stress during driving. Under-torqued bolts can lead to component failure, while over-torqued bolts can cause thread damage or component warping. For example, an improperly torqued driveshaft bolt could lead to vibration or even complete detachment, posing a significant safety risk.

Q2

What happens if I don't use a torque wrench?

Relying on 'feel' is highly inaccurate and can result in either under- or over-tightening. A torque wrench is a calibrated tool that provides accurate and repeatable torque, ensuring bolts are tightened correctly. Using 'feel' might seem alright initially, but the lack of proper clamping force or excessive pressure will often lead to issues down the line, such as bolt failure, vibration, and potential component damage, especially under heavy loads.

Q3

Do I need to replace bolts after removing them from the drivetrain?

In many cases, yes. Some bolts, particularly those used in critical drivetrain components like the transmission or differential, are designed as 'torque-to-yield' (TTY) or 'stretch bolts.' These bolts are designed to stretch upon tightening, and they should always be replaced after being removed. Reusing TTY bolts can lead to reduced clamping force, leading to failure. It is always best to check the manufacturer's service manual.

Q4

What is the difference between Nm and ft-lb?

Nm (Newton-meters) and ft-lb (foot-pounds) are both units of torque. Nm is the metric unit, while ft-lb is the imperial unit. Most modern torque wrenches can switch between both. Always double-check the specifications and your wrench settings to avoid confusion and incorrect torque applications. For instance, a specification of 100 Nm is not the same as 100 ft-lb; you will get an incorrect torque value.

Q5

What should I do if a bolt feels like it's not tightening correctly?

If a bolt feels spongy or does not tighten smoothly, stop immediately. Do not attempt to force it. It could indicate cross-threading, damage to the bolt, or damage to the threads in the component. Forcing it can cause severe damage that may require extensive repairs. Carefully remove the bolt, inspect both the bolt and the threads for damage, and replace it if necessary. If the component threads are damaged, professional service may be required.

Environmental Considerations

Temperature, humidity, and seasonal effects on torque specifications

Temperature Effects

Includes: High Heat, Cold Weather, Thermal Cycling

Temperature can significantly impact torque values and fastener behavior

Cold Weather

Effects:
  • Increased material brittleness
  • Higher torque required due to thread contraction
  • Reduced thread lubricant effectiveness
Recommendations:
  • Allow components to warm to room temperature when possible
  • Consider using winter-grade thread lubricants
  • Check torque values more frequently during winter months

Hot Weather

Effects:
  • Thermal expansion of components
  • Decreased friction in threads
  • Accelerated lubricant breakdown
Recommendations:
  • Check torque when components are at normal operating temperature
  • Use temperature-resistant thread lockers
  • Consider re-torquing after heat cycles

Humidity and Corrosion

Covers: Rust Prevention, Salt Exposure, Moisture Control

Moisture and corrosion can affect fastener integrity and torque values

High Humidity

Effects:
  • Accelerated corrosion formation
  • Reduced friction coefficient
  • Potential thread seizing
Prevention:
  • Use corrosion-resistant fasteners
  • Apply appropriate anti-seize compounds
  • Maintain proper protective coatings

Salt Exposure

Effects:
  • Rapid corrosion development
  • Thread damage
  • Seized fasteners
Prevention:
  • Regular underbody washing
  • Use of sacrificial anodes where appropriate
  • Application of protective coatings

Seasonal Maintenance

Spring, Summer, Fall, and Winter maintenance schedules

Spring

  • Inspect for winter damage
  • Clean and protect exposed fasteners
  • Check torque on critical components

Summer

  • Monitor heat-affected components
  • Check expansion-related loosening
  • Inspect cooling system mounts

Fall

  • Prepare for winter conditions
  • Apply corrosion protection
  • Verify all fasteners are properly torqued

Winter

  • More frequent inspection of critical fasteners
  • Check for salt damage
  • Monitor suspension component torque

Related Resources

Tools, service procedures, and technical bulletins

Recommended Tools

Torque Wrench (1/2" Drive)

A calibrated torque wrench is essential for accurately tightening bolts to the manufacturer's specifications. 1/2" drive is commonly used for drivetrain components.

  • Click-type mechanism for accurate torque setting
  • Wide torque range to accommodate various bolt sizes
  • Durable construction for long-term use
Learn more

Torque Wrench (3/8" Drive)

A 3/8" drive torque wrench is useful for smaller bolts and fasteners that might be encountered in drivetrain service.

  • Click-type mechanism for accurate torque setting
  • Suitable for lower torque range applications
  • Compact design for access in tight spaces
Learn more

Socket Set (Metric)

A comprehensive set of metric sockets is required to fit the various bolt head sizes found in the drivetrain.

  • Wide range of sizes to fit various bolts and nuts
  • 6-point sockets for better grip and reduced risk of slippage
  • Durable construction for professional use
Learn more

Extension Bars

Extension bars are used to reach fasteners that are difficult to access with a standard socket.

  • Various lengths available for different applications
  • Durable construction for use with high torque
  • Secure connection to sockets and ratchets
Learn more

Universal Joint

Universal joints allow you to reach fasteners at an angle.

  • Allows sockets to be used at an angle
  • Durable construction to handle high torque
  • Provides access to hard-to-reach bolts
Learn more

Breaker Bar

A breaker bar is used to initially loosen tight bolts and nuts.

  • Provides high leverage for breaking stubborn fasteners
  • Durable construction for high torque applications
  • Long handle for increased torque application
Learn more
Service Procedures

Front Axle Driveshaft Bolt Torque Procedure

This procedure outlines the steps for properly torquing the bolts securing the front axle driveshaft to the transmission and wheel hub.

  • Identify the specific bolts to be torqued.
  • Clean all bolt threads and mating surfaces.
  • Consult the vehicle's repair manual for the correct torque specification.
  • Using the appropriate socket and torque wrench, tighten the bolts to the specified torque in the specified sequence (if applicable).
  • Recheck the torque after a short run to ensure it remains correct.
View full procedure

Rear Differential Mounting Bolt Torque Procedure

This procedure outlines the steps for properly torquing the bolts securing the rear differential to the chassis.

  • Identify the specific mounting bolts.
  • Clean all bolt threads and mating surfaces.
  • Consult the vehicle's repair manual for the correct torque specification.
  • Using the appropriate socket and torque wrench, tighten the bolts to the specified torque in a cross pattern.
  • Recheck the torque after a short run to ensure it remains correct.
View full procedure

Transmission Mounting Bolt Torque Procedure

This procedure outlines the steps for properly torquing the bolts securing the transmission to the engine.

  • Identify the specific transmission mounting bolts.
  • Clean all bolt threads and mating surfaces.
  • Consult the vehicle's repair manual for the correct torque specification.
  • Using the appropriate socket and torque wrench, tighten the bolts to the specified torque in the specified sequence (if applicable).
  • Recheck the torque after a short run to ensure it remains correct.
View full procedure

Propeller Shaft Bolt Torque Procedure

This procedure outlines the steps for properly torquing the bolts securing the propeller shaft (driveshaft) to the transmission and rear differential.

  • Identify the specific bolts to be torqued on each end of the driveshaft.
  • Clean all bolt threads and mating surfaces.
  • Consult the vehicle's repair manual for the correct torque specification.
  • Using the appropriate socket and torque wrench, tighten the bolts to the specified torque in the specified sequence (if applicable).
  • Recheck the torque after a short run to ensure it remains correct.
View full procedure
Technical Service Bulletins

Drivetrain Vibration Diagnosis and Repair

2020-07-15

This bulletin addresses drivetrain vibration issues, including improper torque on driveshaft and differential bolts which can cause imbalance or noise.

2018-2020 Audi A8 (D5 Chassis)

Resolution: Verify proper torque on all drivetrain fasteners, inspect for worn components, and rebalance driveshafts as needed.

Differential Oil Leakage Caused by Bolt Loosening

2021-03-01

This bulletin addresses instances of differential oil leaks which can be attributed to improperly torqued differential mounting bolts. Check all mounting and axle bolt torques.

2018-2021 Audi A8 (D5 Chassis)

Resolution: Replace any leaking seals, and tighten differential mounting bolts to the specifications outlined in the service manual and recheck torque after driving.

Transmission Mount Bolt Fatigue and Replacement

2022-11-20

This bulletin outlines the potential for transmission mount bolts to fatigue over time. Inspection during service is recommended and a one time use policy should be adhered to.

2018-2022 Audi A8 (D5 Chassis)

Resolution: Inspect transmission mount bolts for fatigue. Replace bolts with new parts and torque to specifications. Follow specified bolt tightening procedure.

About the Author

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Alan Montanye - Automotive Technical Specialist
ASE

Alan Montanye

Automotive Technical Specialist

ASE Master Certified Technician with over a decade of hands-on experience in automotive repair and diagnostics.

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Technical Information
  • All specifications, including torque values, fluid capacities, and maintenance procedures, should be verified against your vehicle's factory service manual.
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