Clutch hydraulic system
Clutch hydraulic system refers to the hydraulic clutch release system used in manual-transmission Pontiac Fiero models.
The Fiero does not use a mechanical clutch cable. Instead, clutch pedal movement is transferred hydraulically from the clutch master cylinder at the front of the car to the clutch slave cylinder at the transmission.
Overview
Manual-transmission Fieros use a hydraulic system to operate the clutch.
When the driver presses the clutch pedal, the Clutch master cylinder pushes fluid through a hydraulic line to the Clutch slave cylinder. The slave cylinder then moves the clutch release arm, which releases the clutch.
A properly working hydraulic system is essential for clean shifting. If the hydraulic system does not move the slave cylinder far enough, the clutch may not fully disengage.
Incomplete clutch release can cause hard shifting, gear clash, grinding, or difficulty selecting reverse even when the transmission itself is not damaged.
Related topics:
- Clutch
- Manual transmission
- Clutch master cylinder
- Clutch slave cylinder
- Clutch bleeding
- Grinding gears
Location
Image wanted: Photo or diagram showing the Fiero clutch hydraulic system, including the clutch master cylinder, hydraulic line, flexible hose sections, slave cylinder, and release arm.
The clutch master cylinder is mounted at the front of the car near the clutch pedal area.
The hydraulic line runs from the front of the car to the rear engine compartment.
The clutch slave cylinder is mounted at the transmission and operates the clutch release arm.
Because the system runs almost the full length of the car, leaks, trapped air, damaged pipe, damaged flexible hose sections, or poor bleeding can all affect clutch operation.
Main components
The clutch hydraulic system includes:
- Clutch pedal
- Clutch pedal pushrod connection
- Clutch master cylinder
- Fluid reservoir
- Hydraulic clutch pipe
- Flexible hose sections
- Clutch slave cylinder
- Bleeder screw
- Slave-cylinder pushrod
- Clutch release arm
- Related brackets and hardware
The clutch assembly itself is separate from the hydraulic system, but both must work correctly for the clutch to release.
Related topic:
Hydraulic routing
Factory 1988 routing identifies the hydraulic clutch system as including the clutch master cylinder, clutch pedal assembly, clutch slave cylinder, flexible hose sections, and clutch pipe.
The general path is:
- Clutch pedal
- Clutch master cylinder
- Hydraulic pipe / line
- Flexible hose section
- Clutch slave cylinder
- Slave-cylinder pushrod
- Clutch release lever
The exact routing and hardware should be checked against the correct model year and installed transmission.
How the system works
When the clutch pedal is pressed, the master-cylinder pushrod moves the master-cylinder piston.
Early piston movement closes the reservoir port, after which continued piston movement forces fluid through the outlet line toward the slave cylinder.
Fluid pressure moves the slave-cylinder piston outward. The slave-cylinder pushrod then moves the clutch release arm.
When the clutch pedal is released, clutch spring pressure returns the release mechanism and fluid returns toward the master cylinder. Near the end of the master-cylinder return stroke, the reservoir port opens again so fluid can move between the system and reservoir.
Hydraulic fluid
The clutch hydraulic system uses brake fluid.
Use DOT 3 brake fluid or equivalent brake fluid specified for the clutch hydraulic system.
Do not use mineral oil, paraffin-base oil, engine oil, automatic transmission fluid, or other non-brake-fluid lubricants in the clutch hydraulic system. Incorrect fluid can damage the rubber parts inside the master and slave cylinders.
Fluid level and condition are important. Low fluid, contaminated fluid, old fluid, or incorrect fluid can cause clutch release problems or damage hydraulic seals.
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Common problems
Common Fiero clutch hydraulic problems include:
- Air in the hydraulic system
- Low clutch fluid
- External fluid leak
- Internal master cylinder bypass
- Master-cylinder rear seal failure
- Master-cylinder center valve seal problem
- Internal slave-cylinder leakage
- External slave-cylinder leakage
- Worn or leaking slave cylinder
- Worn or leaking master cylinder
- Damaged hydraulic pipe
- Damaged flexible hose
- Loose or leaking connections
- Bleeding difficulty
- Insufficient slave-cylinder travel
- Bent or worn clutch pedal
- Worn pushrod or clevis connection
- Incorrect or mismatched replacement parts
- Incorrect master or slave cylinder size
- Overfilled reservoir
Hydraulic problems are often mistaken for transmission problems.
Symptoms
Possible symptoms of clutch hydraulic problems include:
- Hard shifting
- Grinding when selecting gears
- Difficulty selecting first gear
- Difficulty selecting reverse
- Clutch pedal feels soft or spongy
- Clutch pedal goes to the floor
- Little or no pedal resistance
- Clutch engages very close to the floor
- Car creeps forward with the clutch pedal pressed
- Slave cylinder does not move far enough
- Fluid level drops over time
- Visible fluid leak
- Fluid near the master cylinder dust cover
- Fluid near the clutch pedal
- Fluid at the slave cylinder or slave-cylinder boot
- Problem improves temporarily after bleeding
- Reservoir fluid level rises when the pedal is depressed
If the clutch does not fully disengage, the transmission may grind or resist going into gear even if the transmission itself is not damaged.
Air in the system
Air in the clutch hydraulic system is a common cause of poor clutch release.
Because air compresses more than hydraulic fluid, air in the system can reduce slave-cylinder movement.
Possible causes of air in the system include:
- Low fluid level
- Leaking master cylinder
- Leaking slave cylinder
- Loose fittings
- Damaged hydraulic line
- Damaged flexible hose
- Recent hydraulic service
- Incorrect bleeding procedure
A spongy clutch pedal is a common clue that air is present.
Related topic:
Slave-cylinder travel
Slave-cylinder travel is an important diagnostic measurement.
If the slave cylinder does not move far enough when the clutch pedal is pressed, the clutch may not fully release.
Insufficient slave-cylinder travel can be caused by:
- Air in the hydraulic system
- Weak or leaking master cylinder
- Weak or leaking slave cylinder
- Master-cylinder internal bypass
- Damaged hydraulic line
- Damaged flexible hose
- Bent clutch pedal
- Worn pedal linkage
- Worn clevis or pushrod connection
- Incorrect slave cylinder
- Incorrect pushrod or release hardware
When diagnosing hard shifting or gear grinding, slave-cylinder movement should be checked before assuming internal transmission failure.
Master cylinder problems
The clutch master cylinder can fail externally or internally.
External failure may show fluid leakage near the master cylinder, inside the front compartment, or near the clutch pedal area.
Internal failure may allow fluid to bypass the piston seal without an obvious external leak. This can reduce pressure and cause poor slave-cylinder movement.
A useful clue is fluid behavior in the reservoir. If the fluid level in the reservoir rises noticeably as the clutch pedal is depressed, a master-cylinder center valve seal problem may be present.
Related topic:
Slave cylinder problems
The clutch slave cylinder can leak externally or fail internally.
External leakage may be visible at the slave cylinder body, boot, bleeder area, or mounting area.
Internal leakage or seal problems can reduce movement even if the leak is not immediately obvious.
If fluid is found in or around the slave cylinder, the slave cylinder should be inspected carefully.
Related topic:
Clutch pedal and pushrod relationship
Hydraulic problems are not the only cause of poor clutch release.
A bent or worn clutch pedal can reduce master-cylinder travel. Wear at the clutch pedal, pivot, clevis, or pushrod connection can also reduce useful master-cylinder movement.
The clutch pushrod should remain properly aligned with the pedal bracket during operation. The clutch pedal lever and pivot must remain square, and the connection between the pedal and master-cylinder pushrod should not be loose or sloppy.
Related topic:
Bleeding
Bleeding removes air from the clutch hydraulic system.
Fiero clutch bleeding can be difficult if air is trapped in the long hydraulic line or slave cylinder, if the slave cylinder is not positioned favorably, or if the master or slave cylinder is worn.
If the system repeatedly needs bleeding, there is likely an underlying leak, worn cylinder, bad connection, damaged line, or other fault.
Related topic:
Service caution
Before removing the slave cylinder, the master-cylinder pushrod should be disconnected from the clutch pedal.
If the slave cylinder is removed and the clutch pedal is depressed, the slave cylinder can be damaged.
This is especially important during clutch, transmission, slave-cylinder, or bracket work.
Diagnosis
Basic diagnostic checks include:
- Check the clutch fluid level.
- Inspect the fluid condition.
- Look for leaks at the master cylinder.
- Look for fluid near the clutch pedal or master-cylinder dust cover.
- Look for leaks at the slave cylinder.
- Inspect the hydraulic pipe and flexible hose sections.
- Check hydraulic connections for leaks.
- Check clutch pedal travel.
- Inspect the clutch pedal for bending, wear, or looseness.
- Inspect the master-cylinder pushrod connection.
- Check slave-cylinder movement.
- Bleed the system if air is suspected.
- Recheck slave-cylinder movement after bleeding.
- Determine whether the problem is hydraulic, mechanical, cable-related, or internal to the clutch/transmission.
A hydraulic diagnosis should be done before replacing the clutch or transmission.
If clutch operation improves after bleeding but then deteriorates again, inspect for hydraulic pressure loss rather than repeating the same bleeding procedure indefinitely. The master cylinder, slave cylinder, fittings, bleeder screw, hydraulic line, flexible hose sections, and pedal/pushrod geometry should all be checked.
Hydraulic diagnosis clues
| Symptom | Possible cause | Notes |
|---|---|---|
| Pedal travels to the floor with little or no pressure | No fluid, leaking pipe or hose, leaking connection, faulty master cylinder, or faulty slave cylinder | Check fluid level and inspect the full hydraulic system |
| Pedal travels to the floor and fluid is present at the master-cylinder dust cover | Master-cylinder rear seal failure | Inspect or replace the master cylinder, then bleed the system |
| Pedal travels to the floor and the reservoir fluid level rises as the pedal is pressed | Master-cylinder center valve seal problem | Indicates possible internal master-cylinder fault |
| Fluid is present near the master cylinder and clutch pedal | Master-cylinder rear seal failure | May leak into the pedal/front compartment area |
| Fluid is present at the slave cylinder or on the cylinder body | Slave-cylinder seal problem | Inspect or replace the slave cylinder, then bleed the system |
| Pedal feels spongy | Air in the system | Check fluid level, bleed, and inspect for the reason air entered |
| Pedal effort is high with long pedal travel | Incorrect master or slave cylinder size | Verify correct parts for the installed transmission and model year |
| Pedal effort and travel are normal, but gears cannot be selected | Clutch mechanism or transmission problem | Check clutch, shifter, cables, and transmission diagnosis |
| Clutch slips | Worn clutch disc, hydraulic fault, or overfilled reservoir | Do not assume the hydraulic system is the only cause |
| Pedal effort and travel are normal, but shifting is difficult | Clutch mechanism, transmission, or clevis/linkage wear | Inspect mechanical clutch and shift system as well as hydraulics |
Relationship to shifting problems
Many Fiero shifting problems are caused by incomplete clutch release.
If the clutch does not fully disengage, the transmission input shaft may continue turning when the driver tries to shift. This can cause grinding, hard shifting, or difficulty selecting reverse.
Common complaints that may be hydraulic-related include:
- “It will not go into gear.”
- “It grinds going into reverse.”
- “It shifts fine with the engine off, but not with the engine running.”
- “The pedal feels soft.”
- “The clutch pedal goes to the floor.”
- “Bleeding helped for a while, but the problem came back.”
Related topics:
Relationship to transmission type
The clutch hydraulic system is used with all factory manual Fiero transmissions:
Parts and details may vary by model year, engine, and transmission, so replacement parts should be matched to the actual installed transmission and clutch hardware.
Relationship to shift cables
Clutch hydraulic problems and shift cable problems can produce similar symptoms.
A hydraulic problem may prevent the clutch from fully releasing.
A cable or shifter problem may prevent the transmission from being fully selected even when the clutch releases correctly.
Useful distinction:
- If the car shifts easily with the engine off but grinds or resists with the engine running, check clutch release first.
- If certain gears cannot be selected even with the engine off, inspect the shifter, shift cables, cable brackets, and transmission linkage.
- If slave-cylinder travel is low, diagnose the hydraulic system before blaming the transmission.
Related topic:
Service notes
When working on the clutch hydraulic system:
- Keep the reservoir full during bleeding.
- Do not allow air to enter the system.
- Use DOT 3 brake fluid or equivalent specified brake fluid.
- Do not use mineral oil or paraffin-base oil.
- Inspect both master and slave cylinders.
- Check for leaks before and after bleeding.
- Verify slave-cylinder travel.
- Inspect the clutch pedal if travel is insufficient.
- Inspect the pushrod and pedal connection.
- Verify that replacement parts match the installed transmission.
- Do not assume a new part is correct or good.
- Do not assume every grinding or hard-shifting problem is an internal transmission failure.
Notes
The Fiero clutch hydraulic system is a common source of shifting complaints.
A careful diagnosis should consider the master cylinder, slave cylinder, hydraulic pipe, flexible hose sections, pedal, pushrod connection, bleeding procedure, release arm, clutch assembly, shift cables, and transmission together.