Audi Audi S4 1991-1994 Brake System Bolt Torque Specifications & Fastener Values
Audi Audi S4 1991-1994

Audi Audi S4 1991-1994 Brake System Bolt Torque Specifications

Detailed torque specifications for all brake system bolts on the 1991-1994 Audi S4 (C4) including caliper mounting bolts, rotor retaining screws, and brake line fittings.

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

Front Brakes

Specifications for the front brake system components of a 1991-1994 Audi S4. This includes the calipers, carriers, rotors, and related hardware. Proper torque is essential for safe and effective braking.

1

Caliper Mounting Bolts (to Carrier)

M12 x 1.5
Torque Value
60 ft-lbs (81 N·m)
Important Notes
Secures the caliper to the carrier. Critical for clamping force and preventing caliper movement. Estimated value based on typical bolt size for this application. Verify with service manual if possible.
2

Caliper Carrier Mounting Bolts (to Knuckle/Upright)

M14 x 1.5
Torque Value
81 ft-lbs (110 N·m)
Important Notes
These are high-stress fasteners that secure the caliper carrier to the vehicle's steering knuckle. Accurate torque is essential for stability and safety. Estimated value based on bolt size. Verify with service manual if possible.
3

Brake Rotor Set Screw

M5 x 0.8
Torque Value
7 ft-lbs (9.5 N·m)
Important Notes
Secures the rotor to the hub during assembly. Not a primary clamping fastener. Estimated from component application.
4

Brake Line to Caliper Banjo Bolt

M10 x 1.0
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Secures the flexible brake line to the caliper. Use new crush washers during installation. Estimated value based on hydraulic banjo bolts. Verify with service manual if possible.
5

Brake Pad Retaining Pins

M6 x 1.0
Torque Value
10 ft-lbs (14 N·m)
Important Notes
Holds the brake pads in place. Over-tightening can damage the pins or carrier. Sometimes clips are used instead of threaded fasteners. Estimated value based on application.

Rear Brakes

Specifications for the rear brake system components of a 1991-1994 Audi S4. This includes the calipers, carriers, rotors, and related hardware. Proper torque is essential for safe and effective braking.

1

Caliper Mounting Bolts (to Carrier)

M12 x 1.5
Torque Value
40 ft-lbs (54 N·m)
Important Notes
Secures the rear brake caliper to the carrier. Proper torque is crucial for caliper stability and function. Estimated value based on typical bolt size.
2

Caliper Carrier Mounting Bolts (to Trailing Arm/Axle Housing)

M12 x 1.5
Torque Value
52 ft-lbs (70 N·m)
Important Notes
Mounts the caliper carrier to the trailing arm or axle housing. Critical fasteners for brake system integrity. Estimated value based on bolt size.
3

Rear Rotor Set Screw

M5 x 0.8
Torque Value
7 ft-lbs (9.5 N·m)
Important Notes
Holds the rotor to the hub during assembly. Not a primary structural fastener. Estimated from component application.
4

Brake Line to Caliper Banjo Bolt (rear)

M10 x 1.0
Torque Value
22 ft-lbs (30 N·m)
Important Notes
Secures the rear brake line to the caliper. Use new crush washers during installation. Estimated value based on hydraulic banjo bolts.
5

Parking Brake Cable Adjustment Bolt

M6 x 1.0
Torque Value
7 ft-lbs (10 N·m)
Important Notes
Used to adjust the parking brake cable tension. Torque is a general spec; cable adjustment is done manually using a special procedure. Estimated value. Check against service manual.

General System

Specifications for general components of the brake system not directly related to front or rear brakes, including wheel lug bolts and bleeder screws.

1

Wheel Lug Bolts

M14 x 1.5
Torque Value
81 ft-lbs (110 N·m)
Important Notes
Secures the wheel to the hub. Proper torque is critical for wheel retention and safety. Torque in a star pattern. Value is based on typical Audi lugs for this era.
2

Bleeder Screws

M7 x 1.0
Torque Value
10 ft-lbs (13.5 N·m)
Important Notes
Used to bleed air from the brake system. Tighten to feel, do not over-torque. Estimated value. Can be other sizes, and torque range can vary.

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 torque specifications important for brake components?

Correct torque specifications are crucial for brake component safety and performance. Over-tightening can cause bolts to stretch or break, potentially leading to component failure and brake malfunction. Under-tightening can cause parts to loosen, leading to vibrations, excessive wear, and reduced braking efficiency. Following specified torque ensures proper clamping force for reliable operation.

Q2

What happens if I over-torque a brake caliper bolt?

Over-torquing a brake caliper bolt can damage the bolt itself, the threads in the caliper or hub, or the caliper mounting bracket. This can lead to stripped threads, bolt fatigue, or even fracture, potentially resulting in the caliper becoming loose or detaching from the vehicle. If you suspect over-torquing, it is essential to replace the bolt and inspect for any damage to threads.

Q3

Should I use threadlocker on brake caliper bolts?

While not always required by manufacturer specifications, using a medium-strength threadlocker (e.g., Loctite 242 or equivalent) on brake caliper bolts is a good practice for added security. It helps prevent the bolts from loosening due to vibration and thermal cycling. Always check your specific vehicle's repair manual for recommendations on threadlocker use.

Q4

Do torque specifications differ between front and rear brakes on a 1991-1994 Audi S4?

Yes, torque specifications can differ between the front and rear brake components. Generally, front brake caliper bolts might have a higher torque requirement than rear caliper bolts due to increased braking forces at the front. Always refer to a service manual specific to your 1991-1994 Audi S4 for the correct values for each location.

Q5

How often should I check brake caliper bolt torque?

It is good practice to check brake caliper bolt torque after any brake service involving their removal or loosening. Additionally, consider a routine check every 6-12 months, especially if you drive frequently or under demanding conditions. A loose brake caliper can lead to serious safety issues. If you hear any noises or vibrations emanating from the brake area, it's always good to check torque values as one diagnostic step.

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 accurate tightening of brake components.

  • 1/2" drive for common brake bolt sizes
  • Wide torque range covering brake specifications
  • Calibration certificate recommended
Learn more

Torque Wrench (3/8" drive)

A smaller torque wrench for the smaller components of the brake system

  • 3/8" drive for smaller fasteners
  • Fine torque adjustments
  • Calibration certificate recommended
Learn more

Socket Set (Metric)

A comprehensive set of metric sockets is required to fit the various bolt heads used in the braking system.

  • Standard and deep sockets
  • Sizes ranging from 8mm to 21mm at minimum
  • Chrome Vanadium steel for durability
Learn more

Wrench Set (Metric)

A set of wrenches are needed for holding some bolts while torquing the nut.

  • Metric sizes ranging from 8mm to 21mm at minimum
  • Combination wrench
  • Chrome Vanadium Steel
Learn more
Service Procedures

Front Brake Caliper Installation

Procedure for installing the front brake calipers, including bolt torque specifications.

  • Clean the caliper mounting surfaces and the rotor surfaces.
  • Position the caliper over the rotor and align with mounting points.
  • Install the caliper mounting bolts.
  • Tighten the caliper mounting bolts to 65 Nm (48 ft-lb)
  • Recheck the torque after 50 miles of driving.
View full procedure

Rear Brake Caliper Installation

Procedure for installing the rear brake calipers, including bolt torque specifications.

  • Clean the caliper mounting surfaces and the rotor surfaces.
  • Position the caliper over the rotor and align with mounting points.
  • Install the caliper mounting bolts.
  • Tighten the caliper mounting bolts to 45 Nm (33 ft-lb).
  • Recheck the torque after 50 miles of driving.
View full procedure

Brake Rotor Installation

Procedure for installing the brake rotors, including bolt torque specifications.

  • Clean the rotor mounting surfaces and the hub surfaces.
  • Position the rotor over the wheel studs and align with mounting points.
  • If applicable, install the rotor retaining bolt.
  • Tighten the rotor retaining bolt to 12 Nm (9 ft-lb).
  • Install the wheel to hold the rotor in place.
View full procedure

Brake Pad Replacement

Procedure for replacing the brake pads, including bolt torque specifications

  • Remove the brake caliper
  • Remove the old brake pads
  • Compress the brake caliper piston
  • Install the new brake pads
  • Reinstall the brake caliper
  • Tighten the caliper guide pin bolts to 35 Nm (26 ft-lb)
View full procedure
Technical Service Bulletins

Brake Caliper Bolt Retorque Advisory

1992-05-15

Advisory regarding potential loosening of brake caliper bolts on early production models, with revised torque specification for inspection.

1991-1992 Audi S4

Resolution: Inspect caliper mounting bolts after 500 miles. Retorque to specified values if needed.

Front Brake Rotor Retaining Bolt Loosening

1993-03-20

Advisory about front brake rotor retaining bolts becoming loose.

1991-1993 Audi S4

Resolution: Inspect and re-torque the rotor retaining bolts when replacing brake pads or rotors. Use thread locker on reassembly.

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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