The clutch slave cylinder (usually referred to as the clutch slave pump) is a key component in the clutch system, responsible for converting the hydraulic pressure generated by the master cylinder into mechanical force to push the clutch pressure plate to separate or combine with the clutch disc. When the clutch slave cylinder fails, it usually shows the following symptoms:

1, Clutch does not separate or separation is not complete

Phenomenon: When the clutch pedal is pressed, the clutch cannot be completely disengaged or is still partially connected after being disengaged, resulting in difficulty in shifting gears or gear shifting with tooth beating.

Cause: There may be leakage or blockage inside the clutch slave cylinder, resulting in the hydraulic pressure not being fully transmitted to the clutch pressure plate. In addition, wear and tear of the clutch pressure plate or clutch disc may also cause incomplete separation.

2、Clutch pedal feels heavy

Phenomenon: When depressing the clutch pedal, the pedal feels very heavy and requires force to depress.

Reason: The clutch slave cylinder may be worn or stuck inside, resulting in poor piston movement. In addition, the clutch system in the hydraulic oil deterioration or insufficient may also lead to heavy pedal.

3、Bad clutch return

Phenomenon: After releasing the clutch pedal, the pedal cannot return to the initial position completely.

Reason: The return spring inside the clutch slave cylinder may fail or break, resulting in the piston not being able to fully reset. In addition, air mixed in the clutch line may also lead to poor return.

4、Oil leakage

Phenomenon: Oil leakage from the clutch slave cylinder or related piping.

Reason: The seals of the clutch slave cylinder may be aged or damaged, resulting in hydraulic oil leakage. Oil leakage will not only lead to a decline in clutch performance, but may also cause damage to other parts of the vehicle.

5、Rattling or vibration

Phenomenon: When depressing or releasing the clutch pedal, a strange noise is heard or vibration is felt.

Cause: This may be caused by loose, worn or damaged parts inside the clutch slave cylinder. Rattling and vibration usually indicate a serious problem with the clutch system, requiring immediate inspection and repair.

6、Difficulty in shifting gears

Difficulty in shifting gears: As the clutch cannot be completely disengaged, it will feel difficult to engage the gears when shifting gears, accompanied by a clear sense of impact or the inability to smoothly put into gear.

7. Abnormal power transmission:

In driving, if you find that the engine speed rises but the vehicle speed increases slowly, especially when accelerating or climbing a slope, this may be due to clutch slippage, and the slave cylinder failure is one of the reasons.

8. Difficulty in starting the vehicle: 

It may be difficult to start the vehicle smoothly because the clutch is not working properly.

9. Change in clutch pedal travel: 

A slave cylinder failure may cause the free travel of the pedal (i.e., the travel before the pedal begins to feel resistance) to change.

Measures to be taken in the event of a clutch slave cylinder failure

When a clutch slave cylinder malfunctions, it should be promptly inspected and repaired. The following are some countermeasures:

1. Check the hydraulic fluid: Check that the hydraulic fluid in the clutch system is sufficient and clean. If the hydraulic fluid is insufficient or deteriorated, it should be replenished or replaced promptly.

2. Check the seals: Check whether the seals of the clutch slave cylinder are aged or damaged. If the seals are defective, replace them promptly.

3. Check the return spring: Check whether the return spring inside the clutch slave cylinder is intact. If the return spring fails or breaks, replace it with a new one.

4. Check the clutch pressure plate and clutch disc: If the clutch pressure plate or clutch disc is badly worn, it may also cause the clutch slave cylinder to malfunction. Therefore, when checking and repairing the clutch slave cylinder, also check the wear of the clutch pressure plate and clutch disc.

5. Replace the slave cylinder: If it is determined that the slave cylinder has been damaged, it should be promptly replaced with a new one.

Solving these problems usually involves inspecting and possibly replacing the clutch slave cylinder, as well as inspecting the entire clutch hydraulic system, including the clutch fluid, master cylinder, and associated lines to ensure that there is no air in the system and that the hydraulic fluid is in good condition. Repairs should be carried out by a professional technician to ensure safety and performance.

How to repair the clutch slave cylinder

Repairing the clutch slave cylinder (clutch slave pump) usually involves the following steps. Please note that these steps may require specialised tools and knowledge, so it is recommended that they are carried out by a professional automotive service technician:

I. Inspection and Diagnosis

1. Symptom analysis: First, make a preliminary judgement based on the possible failure symptoms of the clutch slave cylinder (e.g. clutch not disengaging, heavy pedal, oil leakage, etc.).

2. Appearance inspection: check whether there is obvious damage, oil leakage or oil seepage in the clutch slave cylinder and its connecting pipeline.

3. Function test: Observe the push rod stroke and reaction of the clutch slave cylinder by depressing the clutch pedal to judge whether it works normally.

Disassembly and cleaning

1. Discharge hydraulic oil: Before disassembling the clutch slave cylinder, it is necessary to discharge the hydraulic oil in the clutch system to avoid further damage to the system caused by oil and impurities.

2. Disassemble the slave cylinder: Use appropriate tools to disassemble the clutch slave cylinder, taking care to protect the surrounding parts from damage.

3. Clean the parts: Thoroughly clean the disassembled clutch slave cylinder and its related parts to remove oil and impurities.

Checking and replacing the clutch slave oil

1. Check the seals: carefully check whether the seals of the clutch slave cylinder (e.g. leather bowl, O-ring, etc.) are aged, worn or damaged. If the seals are faulty, they must be replaced with new ones.

2. Inspect the piston: Check the piston for wear, scoring or galling. If the piston is defective, the entire clutch slave cylinder assembly may need to be replaced.

3. Replace damaged parts: Depending on the results of the inspection, replace damaged seals, pistons or other related parts. If it is necessary to replace the entire clutch slave cylinder assembly, make sure to select an assembly that matches the original model.

Assembly and commissioning

1. Assemble the slave cylinder: reassemble the replaced seals, piston and other parts into the clutch slave cylinder, make sure all parts are correctly installed and fastened in place.

2. Fill the hydraulic oil: After the assembly is completed, fill the appropriate amount of hydraulic oil into the clutch system and check whether there is any leakage.

3. Function test: reconnect the piping of the clutch slave cylinder and start the vehicle for function test. Depress the clutch pedal and observe whether the clutch disengagement and combining effects return to normal.

V. Precautions

1. Safety first: When carrying out maintenance operations, be sure to comply with safety regulations to ensure personal safety and equipment safety.

2. Professional tools: Use professional tools and equipment for maintenance operations to improve maintenance efficiency and quality.

3. Original parts: When replacing parts, try to use original parts or certified parts to ensure the maintenance quality and vehicle performance.

4. Regular Inspection: Regularly inspect and maintain the clutch slave cylinder and its related parts to find and deal with potential problems in time.

Through the above steps, the repair of the clutch slave cylinder can be completed. However, due to the differences in different models and clutch systems, the specific repair steps and precautions may vary. Therefore, be sure to refer to your vehicle's service manual or consult a professional automotive service technician before performing the repair operation.