Clutch
Clutch refers to the manual-transmission clutch system used in manual-equipped Pontiac Fiero models.
The clutch connects and disconnects engine power from the manual transaxle. In the Fiero, the clutch is operated by a hydraulic system using a clutch pedal, clutch master cylinder, hydraulic line, and clutch slave cylinder.
Overview
Manual-transmission Fieros use a single-disc clutch mounted between the engine and manual transaxle.
When the clutch pedal is released, the clutch disc is clamped between the flywheel and pressure plate, allowing engine power to pass into the transmission.
When the clutch pedal is pressed, the clutch is released so the driver can shift gears or stop the car without stalling the engine.
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Location
Image wanted: Photo or diagram showing the Fiero clutch assembly location between the engine and manual transaxle, or a removed Fiero clutch, pressure plate, flywheel, and throwout bearing.
The clutch assembly is located between the engine and manual transaxle inside the bellhousing area.
The hydraulic clutch slave cylinder is mounted externally on the transmission and operates the clutch release arm.
Main components
The Fiero clutch system includes both mechanical and hydraulic parts.
Major components include:
- Clutch pedal
- Clutch master cylinder
- Hydraulic clutch line
- Clutch slave cylinder
- Clutch release arm
- Throwout bearing
- Clutch fork or release mechanism, depending on transmission
- Pressure plate
- Clutch disc
- Flywheel
A problem with any part of the system can affect shifting, clutch release, or drivability.
Clutch disc
The clutch disc is the friction disc located between the flywheel and pressure plate.
When the clutch is engaged, the disc is clamped tightly and transfers engine torque to the transmission input shaft.
Common clutch-disc problems include:
- Worn friction material
- Oil contamination
- Glazing
- Broken or weak damper springs
- Warped or damaged disc
- Incorrect disc installed
A worn clutch disc can cause slipping, poor acceleration, burning smell, or difficulty transferring power.
Pressure plate
The pressure plate clamps the clutch disc against the flywheel.
When the clutch pedal is pressed, the release mechanism reduces clamping force so the disc can disengage.
Pressure-plate problems can cause:
- Clutch slip
- Poor release
- Chatter
- Noise
- Uneven engagement
- Hard pedal effort
- Difficulty shifting
The pressure plate is usually replaced together with the clutch disc and throwout bearing during clutch service.
Flywheel
The flywheel is bolted to the engine crankshaft and provides the surface against which the clutch disc is clamped.
Flywheel condition is important. A damaged, worn, cracked, grooved, glazed, or incorrectly machined flywheel can cause clutch chatter, poor engagement, or premature clutch wear.
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Throwout bearing
The throwout bearing, also called the release bearing, is used to apply force to the pressure plate release mechanism.
A worn throwout bearing can cause noise, especially when the clutch pedal is pressed.
Common symptoms include:
- Whirring or grinding noise with the clutch pedal pressed
- Noise that changes with pedal position
- Rough clutch operation
- Poor release if the bearing or release system is damaged
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Hydraulic clutch system
The Fiero uses a hydraulic clutch release system rather than a mechanical cable.
The hydraulic system includes:
- Clutch master cylinder
- Hydraulic line
- Clutch slave cylinder
- Fluid reservoir
- Related seals and fittings
When the clutch pedal is pressed, the master cylinder pushes fluid through the hydraulic line to the slave cylinder. The slave cylinder then moves the clutch release arm.
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Clutch pedal
The clutch pedal provides the driver's input to the hydraulic clutch system.
Pedal condition and travel are important. A bent, worn, loose, or incorrectly adjusted pedal can reduce hydraulic travel and prevent the clutch from fully disengaging.
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Clutch release and shifting
A manual-transmission Fiero must fully release the clutch to shift properly.
If the clutch does not fully disengage, the transmission input shaft may continue spinning when the pedal is pressed. This can cause hard shifting, grinding, difficulty selecting first gear, or difficulty selecting reverse.
Clutch-release problems are often mistaken for internal transmission problems.
Common problems
Common Fiero clutch topics include:
- Air in the hydraulic system
- Weak clutch master cylinder
- Weak clutch slave cylinder
- Internal or external hydraulic leaks
- Bent or worn clutch pedal
- Insufficient slave-cylinder travel
- Worn clutch disc
- Slipping clutch
- Clutch chatter
- Throwout bearing noise
- Pressure plate problems
- Incorrect clutch parts
- Contaminated clutch disc
- Poor release after clutch replacement
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Symptoms
Possible clutch-related symptoms include:
- Hard shifting
- Grinding when selecting gears
- Difficulty selecting first gear
- Difficulty selecting reverse
- Clutch slipping under acceleration
- Burning smell
- High engine rpm without matching acceleration
- Clutch pedal feels soft or spongy
- Clutch pedal engages very low or very high
- Car creeps forward with clutch pedal pressed
- Noise when clutch pedal is pressed
- Chatter or vibration during engagement
- Fluid leak near the clutch master or slave cylinder
Diagnosis
Before assuming the manual transmission itself has failed, the clutch system should be checked.
Basic diagnostic checks include:
- Check clutch pedal travel and feel.
- Check fluid level in the clutch master cylinder reservoir.
- Inspect for leaks at the master cylinder.
- Inspect the hydraulic line.
- Inspect for leaks at the slave cylinder.
- Check slave-cylinder movement.
- Check for air in the hydraulic system.
- Inspect the clutch pedal for wear or bending.
- Determine whether the clutch is fully disengaging.
- Determine whether symptoms occur in all gears or only specific gears.
- Check for slipping under load.
- Check for noise that changes with clutch pedal position.
If the clutch does not release fully, shifting problems may occur even if the transmission is otherwise good.
Clutch slipping
A slipping clutch occurs when the clutch disc does not hold firmly between the flywheel and pressure plate.
Possible causes include:
- Worn clutch disc
- Oil-contaminated clutch disc
- Weak pressure plate
- Incorrect clutch parts
- Flywheel surface problems
- Clutch not fully engaging
Symptoms of slipping can include high engine rpm without normal acceleration, burning smell, poor acceleration, or slipping under heavy throttle.
Clutch drag
Clutch drag occurs when the clutch does not fully disengage when the pedal is pressed.
Possible causes include:
- Air in the hydraulic system
- Weak master cylinder
- Weak slave cylinder
- Bent clutch pedal
- Incorrect slave-cylinder travel
- Damaged release mechanism
- Incorrect or defective clutch parts
- Warped clutch disc
- Pilot or input-shaft-related issues, depending on installation
Clutch drag can cause hard shifting, grinding, or difficulty selecting reverse.
Clutch chatter
Clutch chatter is shaking, grabbing, or vibration during clutch engagement.
Possible causes include:
- Contaminated clutch disc
- Warped flywheel
- Damaged pressure plate
- Worn engine or transmission mounts
- Improperly surfaced flywheel
- Incorrect clutch installation
- Damaged or worn clutch disc
Mount problems can sometimes feel like clutch chatter, so the engine and transmission mounts should also be inspected.
Relationship to manual transmissions
The clutch system is used with all manual Fiero transmissions.
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Although the overall clutch function is similar, parts and details can vary by engine, transmission, model year, and replacement parts used.
Relationship to engine swaps
Clutch selection is important in engine-swap cars.
A clutch that works well with a stock 2.5L four-cylinder or 2.8L V6 may not be appropriate for a higher-torque engine.
Engine-swap clutch considerations include:
- Engine torque
- Flywheel compatibility
- Transmission input shaft
- Clutch disc spline count
- Pressure plate fitment
- Release bearing compatibility
- Pedal effort
- Intended use
- Street drivability
- Transmission strength
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Service notes
When working on a Fiero clutch:
- Check the hydraulic system before replacing the clutch.
- Bleed the clutch system carefully if hydraulic work has been done.
- Verify slave-cylinder travel if the clutch does not release.
- Inspect the clutch pedal for wear or bending.
- Replace the throwout bearing during clutch replacement.
- Inspect or resurface the flywheel as appropriate.
- Use parts that match the engine and transmission combination.
- Check engine and transmission mounts if chatter or drivetrain movement is present.
- Do not assume every shifting problem is an internal transmission failure.
Notes
Many Fiero manual-transmission complaints are caused by clutch-release or hydraulic problems rather than by the transmission itself.
A proper diagnosis should consider the clutch pedal, hydraulic system, clutch assembly, shifter, shift cables, mounts, and transmission together.