Clutch slave cylinder
Clutch slave cylinder refers to the hydraulic cylinder mounted at the transmission in manual-transmission Pontiac Fiero models.
The clutch slave cylinder is part of the Clutch hydraulic system. It converts hydraulic pressure from the Clutch master cylinder into mechanical movement at the clutch release arm.
Overview
Manual-transmission Fieros use a hydraulic clutch system rather than a mechanical clutch cable.
When the driver presses the clutch pedal, the clutch master cylinder pushes fluid through the hydraulic line to the clutch slave cylinder. The slave cylinder then moves its pushrod, which operates the clutch release arm.
If the slave cylinder does not move far enough, the clutch may not fully disengage. This can cause hard shifting, grinding, gear clash, or difficulty selecting gears.
A slave-cylinder problem can feel like a master-cylinder problem, air in the system, a clutch-pedal problem, or a transmission problem.
Related topics:
- Clutch
- Clutch hydraulic system
- Clutch master cylinder
- Clutch bleeding
- Clutch pedal
- Manual transmission
Location
Image wanted: Photo showing the clutch slave cylinder mounted on a Fiero manual transmission, preferably showing the pushrod, release arm, bleeder screw, hydraulic line, heat shield, and mounting bracket.
The clutch slave cylinder is mounted in the rear engine compartment on or near the manual transmission.
It is positioned so that its pushrod can move the clutch release arm.
The exact mounting arrangement depends on the transmission type, slave-cylinder bracket, release arm, and related hardware.
Related transmission pages:
Function
The clutch slave cylinder converts hydraulic pressure into mechanical movement.
Basic operation:
- The driver presses the clutch pedal.
- The clutch master cylinder creates hydraulic pressure.
- Fluid pressure travels through the clutch hydraulic line.
- Fluid enters the slave cylinder through its threaded inlet port.
- The slave-cylinder piston moves outward.
- The slave-cylinder pushrod moves the clutch release arm.
- The clutch release mechanism disengages the clutch.
When the clutch pedal is released, the slave cylinder returns to its resting position as the clutch release mechanism and hydraulic system return.
Relationship to the master cylinder
The clutch slave cylinder works together with the Clutch master cylinder.
The master cylinder creates hydraulic pressure and fluid movement. The slave cylinder receives that pressure and converts it back into mechanical movement at the transmission.
A problem with either cylinder can reduce clutch release travel. A weak slave cylinder can cause symptoms similar to a weak master cylinder, air in the hydraulic system, poor bleeding, or a bent clutch pedal.
Hydraulic routing
The hydraulic clutch system runs from the front of the car to the rear engine compartment.
The system includes:
- Clutch pedal
- Clutch master cylinder
- Clutch pipe
- Flexible hose sections
- Clutch slave cylinder
- Clutch release lever
The slave cylinder is connected to the master cylinder by the clutch hydraulic pipe and hose assembly.
Related topic:
Hydraulic fluid
The clutch slave cylinder uses brake fluid as part of the clutch hydraulic system.
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 can allow air into the system. Contaminated or incorrect fluid can damage seals and cause hydraulic problems.
Related topics:
Slave-cylinder travel
Slave-cylinder travel is one of the most important checks when diagnosing Fiero clutch problems.
If the slave cylinder does not move far enough when the clutch pedal is pressed, the clutch may drag instead of fully releasing.
Insufficient slave-cylinder travel can cause:
- Hard shifting
- Grinding when selecting gears
- Gear clash
- Difficulty selecting first gear
- Difficulty selecting reverse
- Car creeps forward with clutch pedal pressed
- Shifting improves after pumping the pedal
- Shifting is easier with the engine off than with the engine running
If slave travel is insufficient, the cause may be the slave cylinder, master cylinder, air in the system, hydraulic line, flexible hose, clutch pedal, pushrod, release arm, or clutch mechanism.
Common problems
Common clutch slave cylinder problems include:
- External fluid leak
- Slave-cylinder plunger seal failure
- Internal seal leakage
- Worn bore
- Air trapped in the slave cylinder
- Bleeder screw problems
- Damaged or incorrect pushrod
- Incorrect slave cylinder
- Poor mounting bracket condition
- Incorrect or loose bracket
- Poor bleeding after replacement
- Corrosion inside the cylinder
- Dust boot damage
- Heat shield missing or damaged
- Incorrect part for the installed transmission
A slave cylinder can fail externally or internally. It may leak visibly, or it may fail to move the pushrod far enough even if the leak is not obvious.
Symptoms
Possible symptoms of clutch slave cylinder problems include:
- Hard shifting
- Grinding when selecting gears
- Difficulty selecting first gear
- Difficulty selecting reverse
- Clutch pedal feels soft or spongy
- Clutch engages close to the floor
- Slave-cylinder pushrod movement is too short
- Fluid leak at the slave cylinder
- Fluid inside or around the slave boot
- Fluid on the slave-cylinder body
- Problem improves temporarily after bleeding
- Problem returns after a short time
- Car creeps forward with clutch pedal pressed
These symptoms can also be caused by the master cylinder, air in the line, clutch pedal problems, release-arm problems, shift cable problems, or mechanical clutch problems.
External leaks
An external slave-cylinder leak may show fluid around the slave cylinder, under the dust boot, near the bleeder screw, or around the hydraulic line fitting.
If fluid is present inside the slave cylinder or on the cylinder body, the slave-cylinder plunger seal may be faulty.
A leaking slave cylinder can allow fluid out and air into the system, causing poor clutch release.
Internal leakage
A slave cylinder may fail internally without an obvious external leak.
Internal leakage or seal problems can reduce pushrod movement and prevent full clutch release.
Possible signs include:
- Insufficient slave-cylinder travel
- Soft or inconsistent pedal feel
- Shifting improves after pumping the pedal
- Bleeding helps temporarily
- No obvious leak, but clutch release remains poor
- Release arm moves at first but slowly returns while the clutch pedal is held down
Internal leakage should be considered when the system appears dry but slave-cylinder movement is still inadequate.
Bleeder screw
The slave cylinder has a bleeder screw used to remove air from the clutch hydraulic system.
Bleeder screw problems can include:
- Rounded or damaged bleeder
- Loose bleeder allowing air entry
- Blocked bleeder passage
- Corrosion
- Leakage around the bleeder
If the bleeder screw does not seal correctly, the system may continue to draw air or leak fluid.
Related topic:
Pushrod and release arm
The slave-cylinder pushrod transfers movement from the slave piston to the clutch release arm.
Pushrod length, position, and condition matter. A missing, incorrect, bent, or poorly seated pushrod can reduce clutch release travel.
During installation, the slave-cylinder pushrod must be properly piloted into the clutch release lever.
The release arm and related hardware should also be inspected for wear, damage, looseness, or incorrect installation.
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Mounting bracket and heat shield
The slave cylinder mounts to a bracket at the transmission.
The bracket, heat shield, clutch release lever, and related bolts are part of the slave-cylinder mounting arrangement. If the bracket is bent, loose, cracked, incorrect, or missing hardware, the slave cylinder may move instead of transferring full travel to the release arm.
A missing or damaged heat shield can expose the slave cylinder to excess heat from the engine compartment or exhaust area.
Bracket and heat-shield condition should be checked whenever the slave cylinder is replaced or when slave-cylinder movement seems inconsistent.
Service caution
Before removing the slave cylinder, the master-cylinder pushrod should be disconnected from the clutch pedal.
If the slave cylinder is disconnected and the clutch pedal is depressed, the slave cylinder can be permanently damaged.
This caution is important during slave-cylinder replacement, clutch work, transmission work, release-arm work, or bracket work.
Transmission differences
The clutch slave cylinder arrangement can differ depending on the manual transmission installed.
Factory manual transmissions include:
When ordering replacement parts, identify the actual installed transmission rather than relying only on model year or engine.
A part that bolts on may still be incorrect for the installed transmission, bracket, pushrod, or release-arm arrangement.
Related topic:
Diagnosis
Basic diagnostic checks include:
- Check clutch fluid level.
- Inspect fluid condition.
- Inspect the slave cylinder for external leaks.
- Pull back the slave boot carefully and check for fluid.
- Inspect the slave-cylinder body for fluid.
- Inspect the bleeder screw.
- Inspect the hydraulic line fitting at the slave cylinder.
- Inspect the flexible hose section.
- Check slave-cylinder pushrod movement.
- Inspect the pushrod and release arm.
- Inspect the slave-cylinder mounting bracket.
- Inspect the heat shield.
- Check for air in the hydraulic system.
- Inspect the clutch master cylinder.
- Inspect the clutch pedal and pedal travel.
- Determine whether the clutch is fully disengaging.
A clutch slave-cylinder diagnosis should include the rest of the hydraulic system. Replacing the slave cylinder may not solve the problem if the master cylinder is weak, the pedal is bent, air remains trapped in the line, the bracket moves, or the release mechanism is faulty.
Hydraulic diagnosis clues
| Symptom | Possible cause | Notes |
|---|---|---|
| Pedal travels to the floor with little or no resistance | No fluid, leaking pipe or hose, leaking connection, faulty master cylinder, or faulty slave cylinder | Inspect the full hydraulic system before bleeding |
| Fluid is found at the slave cylinder or on the cylinder body | Slave-cylinder plunger seal failure | Service 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 size master or slave cylinder | Verify correct parts for the installed transmission and model year |
| Pedal effort and travel are normal, but gears cannot be selected | Clutch mechanism, shift system, or transmission problem | Check clutch, shifter, cables, and transmission diagnosis |
| 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 |
Replacement
Replacing the clutch slave cylinder generally involves disconnecting the hydraulic line, removing the slave cylinder from its mounting bracket, installing the replacement cylinder, reconnecting the hydraulic line, filling the reservoir, and bleeding the clutch hydraulic system.
General replacement considerations:
- Match the replacement slave cylinder to the actual transmission.
- Protect painted surfaces from brake fluid.
- Avoid introducing dirt into the hydraulic system.
- Inspect the pushrod and release arm.
- Make sure the pushrod is correctly positioned in the release lever.
- Inspect the mounting bracket.
- Inspect the heat shield.
- Bleed the system thoroughly after installation.
- Recheck for leaks after repair.
- Verify slave-cylinder travel after bleeding.
Related topic:
Bleeding after replacement
After replacing the clutch slave cylinder, the hydraulic system must be bled.
Air trapped in the slave cylinder is a common reason for poor clutch release after service.
If the system is difficult to bleed or the problem returns, check for:
- Air trapped in the slave cylinder
- Loose fittings
- Weak clutch master cylinder
- Incorrect bleeding procedure
- Damaged hydraulic line
- Damaged flexible hose
- Incorrect slave cylinder
- Incorrect pushrod
- Release-arm problems
- Bracket movement
- Bleeder screw leakage
Related topic:
Relationship to shifting problems
A weak or leaking clutch slave cylinder can cause shifting complaints that feel like transmission problems.
Common complaints include:
- “It shifts fine with the engine off, but not with the engine running.”
- “It grinds going into reverse.”
- “It is hard to get into first gear.”
- “The clutch pedal feels soft.”
- “The slave cylinder barely moves.”
- “Bleeding helped, but the problem came back.”
These symptoms should be diagnosed through the clutch hydraulic system before assuming the transmission itself is damaged.
Related topics:
Relationship to shift cables
A slave-cylinder or hydraulic problem can prevent the clutch from fully releasing.
A shift cable or shifter problem can prevent the transmission from being fully selected.
Useful distinction:
- If the car shifts easily with the engine off but grinds or resists with the engine running, check clutch release and slave-cylinder movement first.
- If certain gears cannot be selected even with the engine off, inspect the shifter, shift cables, cable brackets, and transmission linkage.
- If the slave cylinder moves normally but gear selection is still poor, inspect the clutch mechanism, shifter, cables, and transmission.
Related topic:
Service notes
When working on the clutch slave cylinder:
- Use DOT 3 brake fluid or equivalent specified brake fluid.
- Do not use mineral oil or paraffin-base oil.
- Match the slave cylinder to the actual transmission.
- Disconnect the master-cylinder pushrod from the clutch pedal before removing the slave cylinder.
- Inspect the bleeder screw.
- Inspect the pushrod and release arm.
- Check that the pushrod is correctly seated in the release lever.
- Check for fluid under the dust boot.
- Inspect the slave-cylinder bracket and heat shield.
- Bleed the system after replacement.
- Verify slave-cylinder travel after bleeding.
- Inspect the master cylinder if symptoms remain.
- Check the clutch pedal if travel is insufficient.
- Do not assume a new slave cylinder automatically fixes all clutch-release problems.
Notes
The clutch slave cylinder is a common part of Fiero clutch-release diagnosis, but it should not be evaluated by itself.
The master cylinder, slave cylinder, hydraulic line, flexible hose sections, clutch pedal, bleeding procedure, release arm, slave-cylinder bracket, heat shield, clutch assembly, shift cables, and transmission should be considered together.
Some replacement slave cylinders use different seal designs or may vary in quality. If a newly replaced slave cylinder still allows air entry, leaks, or does not provide enough travel, the part itself should not automatically be assumed good.