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.
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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.
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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:
- Fill the clutch master cylinder reservoir.
- Open the slave cylinder bleeder screw.
- Move fluid and air out through the bleeder.
- Close the bleeder screw.
- Keep the reservoir from running dry.
- 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
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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:
- Bleed the master cylinder and hydraulic line first.
- Keep the master cylinder reservoir full.
- Open or remove the slave bleeder as appropriate for the method being used.
- Push the slave cylinder pushrod fully into the slave cylinder.
- Close or reinstall the bleeder while the pushrod is held in.
- Release the pushrod and guide it back into position on the release arm.
- Recheck fluid level and 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:
- Fill the master cylinder reservoir.
- Attach a clear hose to the slave cylinder bleeder screw.
- Open the bleeder screw.
- Allow fluid and air to flow out.
- Keep the reservoir full.
- 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:
- Fill the master cylinder reservoir.
- Attach a clear hose to the slave cylinder bleeder screw.
- Have one person press the clutch pedal.
- Open the bleeder screw to release fluid and air.
- Close the bleeder screw before the pedal is released.
- Release the pedal.
- Refill the reservoir as needed.
- 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.
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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.
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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.