Audi Audi S4 1991-1994 Drivetrain Bolt Torque Specifications & Fastener Values
Audi Audi S4 1991-1994

Audi Audi S4 1991-1994 Drivetrain Bolt Torque Specifications

Detailed torque specifications for bolts related to the drivetrain of the 1991-1994 Audi S4, including transmission, differential, and driveshaft 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

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Search by component name, bolt size, or description

Torque Calculator

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Transmission

This section covers torque specifications for the transmission and its related components. These specifications are critical for ensuring proper sealing, alignment, and secure mounting of the transmission.

1

Transmission-to-Engine Bolts

M12 x 1.5
Torque Value
59 ft-lbs (80 N·m)
Important Notes
Critical for securing the transmission to the engine block. Ensures proper alignment and prevents separation.
2

Transmission Mount Bolts

M10 x 1.5
Torque Value
44 ft-lbs (60 N·m)
Important Notes
Secures the transmission to the chassis, damping vibrations and maintaining alignment.
3

Transmission Case Bolts (General)

M8 x 1.25
Torque Value
18 ft-lbs (25 N·m)
Important Notes
Secures the transmission case halves and other auxiliary components to the transmission case itself.
4

Transmission Drain Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Ensures proper sealing and prevents fluid leakage. Use new crush washer.
5

Transmission Fill Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Ensures proper sealing and prevents fluid leakage. Use new crush washer.
6

Shift Linkage Bolts

M8 x 1.25
Torque Value
18 ft-lbs (25 N·m)
Important Notes
Secures the shift linkage components for precise shifting.
7

Output Flange Bolts (To driveshaft)

M8 x 1.25
Torque Value
25 ft-lbs (34 N·m)
Important Notes
Connects the output flange to the driveshaft. These bolts can see high torque.

Driveshaft

This section details the torque specifications for the driveshaft components, including the center support bearing and flex disc (guibo) connections. Proper torque is essential for vibration damping and safe power transfer.

1

Driveshaft Center Support Bearing Bolts

M8 x 1.25
Torque Value
20 ft-lbs (27 N·m)
Important Notes
Supports the driveshaft and reduces vibration.
2

Driveshaft Flex Disc Bolts (Guibo Bolts)

M10 x 1.5
Important Notes
Connects the driveshaft to the transmission and rear differential flanges. Critical for vibration and power transfer. Use a star sequence.
3

Driveshaft Flange Bolts (to Rear Differential)

M10 x 1.5
Torque Value
33 ft-lbs (45 N·m)
Important Notes
Connects the driveshaft to the rear differential input flange. Critical for vibration and power transfer.

Rear Differential

This section covers torque specifications for the rear differential components. Proper torque is important for secure mounting, housing integrity, and leak-free operation.

1

Differential Mount Bolts

M12 x 1.5
Torque Value
44 ft-lbs (60 N·m)
Important Notes
Secures the differential to the chassis, damping vibrations and ensuring alignment.
2

Differential Case Bolts

M8 x 1.25
Torque Value
18 ft-lbs (25 N·m)
Important Notes
Secure the differential housing.
3

Differential Drain Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Ensures proper sealing and prevents fluid leakage. Use new crush washer.
4

Differential Fill Plug

M18 x 1.5
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Ensures proper sealing and prevents fluid leakage. Use new crush washer.
5

Differential Output Flange Bolts (to Axles)

M10 x 1.5
Torque Value
59 ft-lbs (80 N·m)
Important Notes
Secures the output flanges to the differential and transfers power to the rear axles.

Axles

This section covers torque specifications for axle and halfshaft components. Proper torque is crucial for reliable power transfer to the wheels and to prevent joint failure.

1

Axle Inner CV Joint Bolts (to Differential)

M10 x 1.5
Torque Value
33 ft-lbs (45 N·m)
Important Notes
Attaches the axle to the differential flange, critical for proper power transfer.
2

Axle Outer CV Joint Bolts (to Wheel Hub)

M10 x 1.5
Torque Value
33 ft-lbs (45 N·m)
Important Notes
Attaches the axle to the wheel hub flange, critical for proper power transfer.
3

Wheel Bearing Hub Bolt (Center axle bolt)

M14 x 1.5
Important Notes
Holds the hub assembly firmly to the axle stub and is critical for wheel bearing health.

Clutch Flywheel

This section provides torque specifications for the clutch and flywheel components, which are critical for proper engine operation and driveline interface. Incorrect torque can result in damage and improper clutch function.

1

Pressure Plate Bolts

M8 x 1.25
Torque Value
18 ft-lbs (25 N·m)
Important Notes
Secures the clutch pressure plate to the flywheel for proper clutch operation. Tighten in a star pattern.
2

Flywheel Bolts

M10 x 1.5
Important Notes
Secures the flywheel to the crankshaft. Critical for proper engine operation and driveline interface. Tighten in a star pattern.

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 is using the correct torque specification important for drivetrain bolts?

Using the correct torque ensures proper clamping force, preventing bolts from loosening due to vibration or fatigue, which can lead to component failure. Over-torquing can stretch or break bolts, while under-torquing can allow parts to move, leading to damage. For example, an improperly torqued driveshaft bolt might come loose, causing severe damage or loss of control.

Q2

Should I use new bolts when reassembling the drivetrain?

Yes, it's generally recommended to use new bolts, especially for critical components like the flywheel, pressure plate, and differential. These bolts often have specific stretch characteristics and can weaken or fail if reused. Old bolts may have been fatigued or stretched, and reusing them can lead to inaccurate torque readings and subsequent failure.

Q3

What type of lubricant should I use on drivetrain bolts?

Typically, bolts are either installed dry or with a specific type of lubricant, as specified by the manufacturer. Using the wrong lubricant can significantly alter torque readings and result in improper clamping force. For the Audi S4, most drivetrain fasteners are installed dry, unless otherwise specified. Using anti-seize on dry-torque fasteners will lead to an incorrect clamping force.

Q4

Do I need to retorque drivetrain bolts after a period of driving?

For some critical components, like the driveshaft or CV joint bolts, it is advisable to check and retorque the bolts after a short period of driving (e.g., 50-100 miles). This ensures proper seating of components and compensates for any settling that might occur. Always consult the service manual for specific recommendations. It is also a good idea to visually inspect these components periodically.

Q5

What should I do if I strip or break a drivetrain bolt?

If a bolt strips or breaks, it is crucial to extract the broken portion properly. Attempting to reuse the stripped threads can lead to a compromised repair. Use appropriate tools to extract the broken portion, and always replace the bolt with a new one of the correct grade. Ensure the new threads are free from debris. This includes using thread repair techniques such as helicoils if necessary.

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 specification.

  • Wide torque range (e.g., 20-200 Nm)
  • Audible click when desired torque is reached
  • Reversible ratchet mechanism
Learn more

Torque Wrench (3/8" Drive)

A smaller calibrated torque wrench for lower torque applications.

  • Lower torque range (e.g., 5-80 Nm)
  • Audible click when desired torque is reached
  • Reversible ratchet mechanism
Learn more

Socket Set (1/2" and 3/8" Drive)

A comprehensive set of sockets in various sizes to fit different bolts and nuts.

  • Metric sizes
  • Chrome vanadium steel construction
  • Deep and standard sockets
Learn more

Extension Bars (1/2" and 3/8" Drive)

Various length extension bars to access bolts in difficult locations.

  • Multiple length options
  • Durable steel construction
  • Secure attachment to sockets and ratchets
Learn more

Universal Joint (1/2" and 3/8" Drive)

Allows sockets to be used at an angle for hard-to-reach bolts.

  • Durable construction
  • Smooth rotation
  • Secure fit
Learn more
Service Procedures

Driveshaft Bolt Tightening

Proper procedure for tightening driveshaft bolts to ensure correct preload and secure connection.

  • Clean all bolt threads and mating surfaces.
  • Apply anti-seize to the bolt threads.
  • Install the driveshaft bolts, tightening them by hand initially.
  • Using a 1/2" drive torque wrench, tighten the bolts to 65 Nm (48 ft-lb).
  • Angle tighten an additional 90 degrees.
  • Verify all bolts are tightened to specified torque and angle.
View full procedure

Transmission Mount Bolt Tightening

Procedure for tightening transmission mount bolts to prevent vibrations and ensure proper alignment.

  • Inspect transmission mount bushings for wear or damage and replace if needed.
  • Install the transmission mount, aligning all holes.
  • Install bolts, tightening them by hand initially.
  • Using a 1/2" drive torque wrench, tighten the mounting bracket to chassis bolts to 25 Nm (18 ft-lb) + 90 degrees.
  • Using a 1/2" drive torque wrench, tighten the mount to transmission bolts to 40 Nm (30 ft-lb).
  • Verify all bolts are tightened to specified torque.
View full procedure

Differential Mount Bolt Tightening

Procedure for tightening differential mount bolts to ensure proper support and alignment of the differential.

  • Inspect differential mount bushings for wear or damage and replace if needed.
  • Install the differential mounts, aligning all holes.
  • Install bolts, tightening them by hand initially.
  • Using a 1/2" drive torque wrench, tighten the mounting bracket to chassis bolts to 25 Nm (18 ft-lb) + 90 degrees.
  • Using a 1/2" drive torque wrench, tighten the mount to differential bolts to 45 Nm (33 ft-lb).
  • Verify all bolts are tightened to specified torque.
View full procedure

Axle Nut Tightening

Procedure for correctly tightening the axle nut on the front hubs.

  • Install the axle nut by hand.
  • Using a 1/2" drive torque wrench, tighten the axle nut to 280 Nm (207 ft-lb)
  • Ensure the nut is properly staked in place using a punch.
View full procedure
Technical Service Bulletins

Driveshaft Bolt Loosening

1995-02-15

Instances of driveshaft bolts loosening prematurely due to incorrect torque application have been reported.

1991-1994 Audi S4

Resolution: Inspect driveshaft bolts for correct torque and angle; re-torque if necessary using the updated procedure: 65 Nm (48 ft-lb) + 90 degrees angle tighten. Apply thread locker (Loctite 242 or equivalent) to the bolts during reinstallation

Differential Mount Bushing Degradation

1996-07-22

Premature degradation of the rubber bushings in the differential mount has been observed, causing excessive play and drivetrain noise.

1991-1994 Audi S4

Resolution: Inspect differential mounts for wear. Replace mounts and hardware if bushings are degraded. Ensure all bolts are tightened to the torque specification 45 Nm (33 ft-lb) after installation.

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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