Clutch bleeding

Clutch bleeding refers to removing air from the clutch hydraulic system in manual-transmission Pontiac Fiero models.

The Fiero uses a hydraulic clutch release system. Air in the system can reduce clutch slave-cylinder movement, preventing the clutch from fully releasing and causing hard shifting, gear clash, grinding, or difficulty selecting gears.

Overview

Manual-transmission Fieros use hydraulic pressure to operate the clutch.

When the clutch pedal is pressed, the Clutch master cylinder pushes fluid through the hydraulic clutch line to the Clutch slave cylinder. The slave cylinder then moves the clutch release arm.

If air is trapped in the hydraulic system, pedal movement may compress the air instead of moving the slave cylinder far enough. This can cause incomplete clutch release.

Bleeding removes air from the system and replaces it with clean brake fluid.

Related topics:

• Clutch
• Clutch hydraulic system
• Clutch master cylinder
• Clutch slave cylinder
• Manual transmission
• Grinding gears

Location

Image wanted: Photo showing the clutch slave cylinder bleeder screw on a Fiero manual transmission, preferably with the slave cylinder, hydraulic line, pushrod, and release arm visible.

The clutch master cylinder is located 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.

The bleeder screw is located on the slave cylinder.

Why bleeding is needed

Bleeding is needed when air enters the clutch hydraulic system.

Common reasons include:

• Low clutch fluid
• Master cylinder replacement
• Slave cylinder replacement
• Hydraulic line replacement
• Flexible hose replacement
• Fluid leak
• Loose fitting
• Bleeder screw problem
• Previous incorrect bleeding
• Old or contaminated fluid

Air in the system can reduce slave-cylinder travel and prevent full clutch release.

Symptoms of air in the system

Possible symptoms include:

• Soft or spongy clutch pedal
• Clutch pedal goes too low
• Clutch pedal goes to the floor
• Clutch engages close to the floor
• Hard shifting
• Grinding when selecting gears
• Difficulty selecting first gear
• Difficulty selecting reverse
• Car creeps forward with the clutch pedal pressed
• Shifting improves temporarily after bleeding
• Slave-cylinder movement is too short

These symptoms can also be caused by a weak master cylinder, weak slave cylinder, bent clutch pedal, damaged hydraulic line, incorrect parts, or a mechanical clutch problem.

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.

Keep the reservoir full during bleeding.

Brake fluid can damage paint, so spills should be cleaned carefully and promptly.

Related topic:

• Brake fluid

Before bleeding

Before bleeding the clutch, inspect the system.

Check:

• Fluid level in the clutch master cylinder reservoir
• Fluid condition
• Master cylinder leaks
• Slave cylinder leaks
• Hydraulic line damage
• Flexible hose damage
• Loose fittings
• Bleeder screw condition
• Clutch pedal condition
• Master-cylinder pushrod connection
• Slave-cylinder pushrod position
• Release arm movement

If the system has a leak or failing hydraulic part, bleeding may only help temporarily.

Basic bleeding concept

The goal of clutch bleeding is to move air out of the hydraulic system without allowing new air to enter.

The basic concept is:

1. Fill the clutch master cylinder reservoir.
2. Open the slave cylinder bleeder screw.
3. Move fluid and air out through the bleeder.
4. Close the bleeder screw before air can be drawn back in.
5. Keep the reservoir from running dry.
6. Repeat until no air remains and slave-cylinder movement is correct.

Different owners and service procedures may use different bleeding methods, but the goal is always the same: remove air and verify that the clutch slave cylinder moves far enough to release the clutch.

Important cautions

When bleeding the clutch hydraulic system:

• Do not let the master cylinder reservoir run dry.
• Do not allow dirt into the reservoir.
• Do not reuse dirty fluid.
• Protect paint from brake fluid.
• Make sure the bleeder screw seals properly.
• Do not overtighten fittings or bleeder screws.
• Verify slave-cylinder movement after bleeding.
• If the problem returns quickly, look for a leak, failing part, or air entering the system.

Some Fiero bleeding methods warn against rapidly pumping the clutch pedal. Pumping can move fluid, but it can also break air into smaller bubbles or temporarily mask a hydraulic problem.

A clutch that still does not release after bleeding may have another problem, such as a weak master cylinder, weak slave cylinder, incorrect slave cylinder, bent clutch pedal, worn pedal hardware, damaged hydraulic line, incorrect parts, or a mechanical clutch problem.

Slave-cylinder 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 caution is especially important during clutch, transmission, slave-cylinder, release-arm, or bracket work.

Slave-cylinder bleeding difficulty

The Fiero clutch slave cylinder can trap air.

Air may remain in the slave cylinder even after fluid appears to come out of the bleeder. This can cause the clutch to feel almost correct but still not release fully.

If bleeding does not restore proper clutch operation, check for:

• Air trapped in the slave cylinder
• Slave cylinder angle or position
• Weak master cylinder
• Weak slave cylinder
• Bleeder screw leakage
• Damaged hydraulic line
• Damaged flexible hose
• Bent clutch pedal
• Incorrect slave cylinder
• Incorrect pushrod
• Release-arm problem

Related topic:

• Clutch slave cylinder

Compressing the slave cylinder

Some Fiero clutch bleeding methods include manually compressing the slave-cylinder pushrod while bleeding the slave cylinder.

The reason is that air can remain trapped inside the slave cylinder, especially near the pushrod end. Compressing the slave piston can help force trapped air out through the bleeder.

General concept:

1. Bleed the master cylinder and hydraulic line first.
2. Keep the master cylinder reservoir full.
3. Open or remove the slave bleeder as appropriate for the method being used.
4. Push the slave cylinder pushrod fully into the slave cylinder.
5. Close or reinstall the bleeder while the pushrod is held in.
6. Release the pushrod and guide it back into position on the release arm.
7. Recheck fluid level.
8. Recheck slave-cylinder travel.

This should be done carefully because the slave cylinder is under spring and hydraulic influence, and brake fluid can spray from the bleeder. Eye protection should be used.

If compressing the slave cylinder still does not restore proper travel, the problem may be elsewhere in the hydraulic system or clutch release mechanism.

Gravity bleeding

Gravity bleeding allows fluid to flow through the system using gravity.

General concept:

1. Fill the master cylinder reservoir.
2. Attach a clear hose to the slave cylinder bleeder screw.
3. Open the bleeder screw.
4. Allow fluid and air to flow out.
5. Keep the reservoir full.
6. Close the bleeder when fluid flows cleanly without air bubbles.
7. Recheck slave-cylinder movement.

Gravity bleeding can be useful, but it may not remove all trapped air from every system.

Pedal bleeding

Pedal bleeding uses clutch pedal movement to push fluid through the system.

General concept:

1. Fill the master cylinder reservoir.
2. Attach a clear hose to the slave cylinder bleeder screw.
3. Have one person press the clutch pedal.
4. Open the bleeder screw to release fluid and air.
5. Close the bleeder screw before the pedal is released.
6. Release the pedal.
7. Refill the reservoir as needed.
8. Repeat until no air appears and clutch operation improves.
9. Verify slave-cylinder movement.

If the bleeder is open while the pedal is released, air may be drawn back into the system.

Vacuum or pressure bleeding

Vacuum or pressure bleeding tools may be used by some owners or shops.

These methods can make bleeding easier, but they can also draw air around loose fittings, worn seals, or bleeder threads if the system is not sealed properly.

If using a bleeding tool, follow the tool instructions and verify final slave-cylinder movement.

Checking slave-cylinder travel

After bleeding, slave-cylinder movement should be checked.

If the slave cylinder does not move far enough, the clutch may not fully disengage.

Insufficient movement can be caused by:

• Air still in the system
• Weak clutch master cylinder
• Weak clutch slave cylinder
• Master-cylinder internal bypass
• Slave-cylinder leakage
• Bent clutch pedal
• Worn pedal linkage
• Damaged hydraulic line
• Damaged flexible hose
• Incorrect replacement parts
• Release-arm or clutch problem

Slave-cylinder travel is often more useful than pedal feel alone.

Related topic:

• Clutch slave cylinder

Holding-pressure check

A useful diagnostic check is to observe the clutch release arm while a helper presses and holds the clutch pedal down.

If the release arm moves normally at first but then slowly moves back while the pedal is still held down, the system may be losing hydraulic pressure.

Possible causes include:

• Internal clutch master cylinder bypass
• Internal clutch slave cylinder leakage
• External fluid leak
• Air in the system
• Loose fitting
• Bleeder screw leakage

This check can help separate a simple bleeding problem from a hydraulic pressure-retention problem.

Clutch pedal height and travel

Clutch pedal travel affects master-cylinder travel, which affects slave-cylinder movement.

If the clutch pedal is bent, worn, incorrectly assembled, or restricted by other pedal-area hardware, the master cylinder may not move enough fluid to fully release the clutch.

A commonly used Fiero check is to compare clutch pedal height with brake pedal height. If the clutch pedal sits too low, clutch release travel may be reduced.

Possible pedal-area problems include:

• Bent clutch pedal
• Worn pedal pivot
• Worn pedal pin
• Incorrect master-cylinder pushrod installation
• Pushrod or banjo installed incorrectly
• Pedal hardware wear
• Interference or misadjustment near the pedal

If slave-cylinder travel is short even after bleeding, the clutch pedal and master-cylinder pushrod should be inspected before assuming the transmission or clutch itself has failed.

Related topic:

• Clutch pedal

Pushrod and pedal geometry

The clutch master cylinder pushrod connection affects clutch pedal travel and hydraulic movement.

If the pushrod, often called the banjo, is installed incorrectly or the pedal geometry is wrong, the master cylinder may not receive full travel. This can reduce slave-cylinder movement and cause poor clutch release.

Checks include:

• Clutch pedal height
• Pedal wear or bending
• Pushrod orientation
• Pedal pivot wear
• Pushrod connection wear
• Full pedal return

If the clutch pedal does not return fully, the master cylinder may not uncover its internal compensation/return port correctly.

If bleeding does not fix the problem

If clutch bleeding does not solve the problem, do not assume the transmission has failed.

Check:

• Master cylinder internal bypass
• Slave cylinder leakage or internal failure
• Air entering through a fitting
• Damaged hydraulic line
• Damaged flexible hose
• Bent clutch pedal
• Incorrect slave cylinder
• Incorrect pushrod
• Release-arm problem
• Worn or damaged clutch assembly
• Shift cable problems
• Transmission mount problems

A problem that improves briefly after bleeding but returns usually indicates an air leak, failing hydraulic part, or unresolved mechanical issue.

Temporary improvement after bleeding

If clutch bleeding improves clutch operation only temporarily, there is usually still an underlying problem.

Possible causes include:

• Air still trapped in the system
• Air being drawn back into the system
• Weak clutch master cylinder
• Weak clutch slave cylinder
• Internal master cylinder bypass
• Internal slave-cylinder leakage
• Loose or leaking fitting
• Bleeder screw not sealing fully
• Damaged hydraulic line
• Damaged flexible hose
• Clutch pedal or pushrod problem

A clutch that works briefly after bleeding but then stops fully disengaging should not be treated as simply “hard to bleed.” The hydraulic system should be inspected for a fault that is allowing pressure loss, air entry, or insufficient slave-cylinder travel.

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 system before bleeding
Pedal travels to the floor and fluid is found at the master-cylinder dust cover	Master-cylinder rear seal failure	Service or replace the master cylinder, then bleed the system
Pedal travels to the floor and reservoir fluid rises as the pedal is pressed	Master-cylinder center valve seal problem	Indicates possible internal master-cylinder fault
Fluid is found near the master cylinder and pedal	Master-cylinder rear seal failure	Inspect the master cylinder and pedal area
Fluid is found at the slave cylinder or 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 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 or transmission problem	Check clutch, shifter, cables, and transmission diagnosis
Clutch slips	Worn clutch disc, hydraulic fault, or overfilled reservoir	Do not assume bleeding alone will solve it
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

Parts and configuration checks

If repeated bleeding does not fix the clutch-release problem, verify that the installed parts match the car's actual transmission and clutch hardware.

Important checks include:

• Correct clutch master cylinder
• Correct clutch slave cylinder
• Correct slave-cylinder pushrod
• Correct slave-cylinder mounting bracket
• Correct transmission identification
• Correct master-cylinder pushrod
• Clutch pedal condition
• Hydraulic line condition
• Flexible hose condition
• Bleeder screw condition

This is especially important on cars that have been modified, repaired, or transmission-swapped.

The Getrag 5-speed, Isuzu 5-speed, and Muncie 4-speed do not all use identical clutch hydraulic parts and brackets. A part that bolts on may still be incorrect for the actual transmission or may not provide the correct travel.

Replacement parts should be matched to the actual transmission.

Relationship to shifting problems

Poor clutch bleeding can cause symptoms 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 will not go into first gear.”
• “The clutch pedal feels soft.”
• “Bleeding helped, but the problem came back.”

These symptoms should be diagnosed through the clutch hydraulic system before replacing the transmission.

Related topics:

• Grinding gears
• Manual transmission
• Clutch hydraulic system

Hidden hydraulic line problems

A clutch hydraulic problem is not always caused by the master cylinder or slave cylinder.

The Fiero clutch hydraulic line runs from the front of the car to the rear engine compartment. Flexible sections, fittings, crimps, or damaged hard line can cause problems that are not immediately obvious.

Possible line-related problems include:

• External fluid leak
• Rusted or damaged hard line
• Damaged flexible hose
• Collapsing flexible hose
• Air entering at a fitting or crimp
• Loose connection
• Previous incorrect repair

If the system repeatedly will not bleed correctly, loses travel, or improves briefly and then gets worse again, inspect the entire hydraulic path from the master cylinder to the slave cylinder.

Service notes

When bleeding the Fiero clutch hydraulic system:

• Keep the reservoir full at all times.
• Use clean DOT 3 brake fluid or equivalent specified brake fluid.
• Watch for air bubbles.
• Check for leaks before and after bleeding.
• Verify slave-cylinder travel.
• Inspect the master and slave cylinders if bleeding does not hold.
• Inspect the clutch pedal if travel is poor.
• Inspect the pushrod and pedal connection.
• Do not assume that pedal feel alone proves the system is fully bled.
• Recheck operation with the engine running.
• Do not assume every hard-shifting problem is caused by the transmission.

Notes

Clutch bleeding is a common Fiero service topic because the long hydraulic line and rear-mounted slave cylinder can make air removal more difficult than on simpler front-engine layouts.

A successful bleed should restore firm pedal feel and enough slave-cylinder movement for the clutch to release fully.

If repeated bleeding does not solve the problem, the diagnosis should expand beyond the bleeding procedure itself. The master cylinder, slave cylinder, clutch pedal, pushrod, hydraulic line, flexible hose sections, release arm, and actual transmission type should all be checked.

See also

• Clutch
• Clutch hydraulic system
• Clutch master cylinder
• Clutch slave cylinder
• Clutch pedal
• Manual transmission
• Grinding gears
• Muncie 4-speed
• Isuzu 5-speed
• Getrag 5-speed
• Transmission identification
• Shift cable