The working principle of the clutch master cylinder
Modern vehicles equipped with manual transmissions use hydraulic fluid (usually brake fluid) to translate the movement of the clutch pedal into the drive of the clutch fork. When you press down on the clutch pedal, a lever attached to the clutch pedal assembly pushes the hydraulic oil in the clutch master cylinder.
Because this fluid is incompressible, it is forced down the clutch line to the driven cylinder, which is connected to the clutch shift fork. Clutch forks force the clutch to separate from the pressure plate and flywheel, allowing the engine and wheels to spin independently.
Top 4 Bad Clutch Master Cylinder Symptoms
Here are the four most common signs that your clutch master cylinder is starting to fail or has completely failed. Please note that the following may only be helpful if you are experiencing hydraulic clutch problems and does not apply to wireline operated clutch systems.
#1 -- Low clutch fluid
The clutch master cylinder will have low and high markings on the side of the reservoir indicating the safe volume of clutch fluid. If your clutch level is below the low mark, it is time to fill. The tank lid or user's manual should tell you which type of liquid to use.
After filling the clutch, pay attention to the fluid level. The clutch level should not decrease over time as you see in brake fluid. The brake level decreases over time as the caliper piston extends further as the brake pads wear, but the clutch does not operate in this way.
Long-term loss of clutch fluid indicates a leakage of the clutch master or slave cylinder.
#2 -- Soft or spongy clutch pedal
Have you noticed that your clutch pedal feels lighter and easier to press down than before? Unlike clutch fluid, air is compressible. If there is air in the clutch master cylinder, the pedals will start to feel very soft even if the clutch seems to be working properly.
Try to bleed the clutch to fix the problem. If the problem recur after a period of time, the clutch master cylinder may be faulty.
#3 -- Participation points suddenly change
On your way to work one morning, you almost stall several times and can't seem to get the car moving without pulling the whole place. You swear you know how to drive a stick, maybe you're just tired.
If you encounter this, it is best to open the hood and check the clutch level.
If the clutch tank is empty, there may be a little oil left in the line to keep you going, but you'll certainly notice a difference in clutch engagement if you're even able to get it into gear.
In this case, the clutch will leave the floor immediately and engage very suddenly.
#4 -- Dark clutch fluid
If you recently replaced the clutch oil and noticed that it suddenly turned very black, an internal seal in the clutch master cylinder may have failed. Rubber fragments in these seals can break down and contaminate the clutch fluid, quickly discolouring the contents of the tank.
If you have not replaced the clutch oil recently, check your user manual for recommended maintenance intervals. The correct way to replace the clutch oil is to flush the system with fresh oil, draining the clutch line in the process.
You can try the following as a quick and dirty test for seal failure:
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Suck the old clutch oil out of the tank (for example, use something like Turkey butter).
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Fill the tank with fresh liquid.
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Wait a few days to see if the new liquid turns black.
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If your fluid turns black within a few days, it could be a seal failure in the clutch master cylinder, especially if you exhibit any of the other symptoms listed above.
