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 system. Air in the system can prevent the clutch from fully releasing, causing hard shifting, 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 line to the Clutch slave cylinder. The slave cylinder then moves the clutch release arm.

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

Related topics:

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

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 clutch slave cylinder is located in the rear engine compartment on or near the manual 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
• 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 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, or mechanical clutch problem.

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
• Loose fittings
• Bleeder screw condition
• Clutch pedal condition
• Slave-cylinder pushrod position
• Release arm movement

If the system has a leak, bleeding may only help temporarily.

Fluid

The clutch hydraulic system uses brake fluid.

Use the correct brake fluid specified for the system. Keep the reservoir full during bleeding.

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

Related topic:

• Brake fluid

Basic bleeding concept

The goal of clutch bleeding is to move air out of the hydraulic system and replace it with fluid.

The basic process 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.
5. Keep the reservoir from running dry.
6. Repeat until no air remains and slave-cylinder travel is correct.

Different owners and service manuals may use different bleeding methods, but the goal is always the same: remove air without allowing more air into the system.

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 specifically warn against rapidly pumping the clutch pedal. Pumping can move fluid, but it can also break air into smaller bubbles or temporarily mask a problem by building pressure only for a short time.

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, or mechanical clutch problem.

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
• Bent clutch pedal
• Incorrect slave cylinder
• Incorrect pushrod
• Release-arm problem

Related topic:

• Clutch slave cylinder

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.

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.

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 travel.

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
• Bent clutch pedal
• Worn pedal linkage
• Damaged hydraulic line
• Incorrect replacement parts
• Release-arm or clutch problem

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

Related topic:

• Clutch slave cylinder

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
• 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.

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

Service notes

When bleeding the Fiero clutch hydraulic system:

• Keep the reservoir full at all times.
• Use clean 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.
• Do not assume that pedal feel alone proves the system is fully bled.
• Recheck operation with the engine running.

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.

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