Symptoms of a Bad Clutch Master Cylinder

Published: July 12, 2022
Last updated: July 13, 2022

Whenever you are driving a 3 pedaled vehicle with a hydraulic clutch, you will be using a clutch master cylinder to connect your left foot to the clutch. It is highly likely that if the master cylinder has completely failed, it will leave you stranded, except if you have figured out a way to limp to your destination without the ability to use the clutch. As a result, it can be especially dangerous if the brakes and clutch share a common reservoir, as you would also be left without your brakes should this happen. 

In most cases, a clutch master cylinder fails because of leaking clutch fluid, and this is the most common mode of failure, which may provide you with some early warning signs before the system completely fails.

How a Clutch Master Cylinder Works

There is a hydraulic fluid used in modern vehicles that have manual transmissions. It is used to convert the movement of the clutch pedal into actuation of the clutch fork by the use of hydraulic fluid (usually brake fluid). The clutch master cylinder is filled with hydraulic fluid when a rod attached to the gear shift pedal assembly is depressed, causing the fluid to push onto the clutch pedal assembly.

There are two components to the clutch system. On one hand, there is the clutch fluid, which is not compressible, and on the other hand, there is the slave cylinder, which is connected to the clutch fork. When the clutch fork is pushed up against the pressure plate, it separates the clutch from the pressure plate and flywheel, allowing the engine and wheels to rotate independently of one another.

Top Symptoms Of A Bad Clutch Master Cylinder

These are the four most common signs that your clutch master cylinder is about to fail or has already failed completely, and here is what you can do about it. It is important to note that the following information is likely to be helpful only if you have an issue with your hydraulic clutch, and does not apply to a system that operates via cable.

1. Low Clutch Fluid

Usually, clutch master cylinders have low and high marks on their reservoirs, to indicate the amount of clutch fluid they should have in their reservoir at any given time. You should top up your clutch fluid if it falls below the low mark, which means your clutch fluid level has gone too low. If you are unsure of what kind of fluid to use, you should look at the reservoir cap or owner's manual on your vehicle.

You should keep an eye on the level of your clutch fluid after you have topped up the fluid. In the same way that the brake fluid level may drop over time, the clutch fluid level shouldn't decrease over time. When you use your brakes, the brake fluid level drops over time because the piston on the brake caliper extends further as your brake pads wear, but with the clutch, the piston does not extend as the clutch operates. It may be indicative that a clutch master or slave cylinder is leaking fluid if you experience a chronic loss of clutch fluid. 

2. Soft/Spongy Clutch Pedal

Do you notice that the pedal on your clutch feels lighter and easier to push than it used to? Does it feel lighter and easier to push? Air is compressible, as opposed to clutch fluid, which is not. When there is too much air in the clutch master cylinder, you will notice that the clutch pedal will feel very soft even though the clutch appears to be working perfectly.

You might be able to resolve the problem by bleeding the clutch. In the event that the issue reappears after a period of time has passed, it could be the clutch master cylinder that is causing the issue.

3. Engagement Point Suddenly Changed

One morning as you were rushing to work, you nearly stalled a couple of times and were having trouble getting the car moving without jerking all over the place as it tried to get moving. It's just that you're tired, maybe you just don't know how to drive a stick. It is highly recommended that you pop the hood on your car and inspect the clutch fluid level if this has happened to you.

You may find that there is a tiny amount of clutch fluid left in the lines even if your clutch fluid reservoir is empty, but you're still going to notice a difference in clutch engagement. If you are even able to engage the clutch at all because there may not be enough fluid in the lines. In such a scenario, the clutch will engage abruptly and right off the floor of the vehicle.

4. Dark Clutch Fluid

There is a possibility that one of the internal seals within the clutch master cylinder is undergoing failure if you have recently changed your clutch fluid, but the color of the fluid has suddenly turned very dark. This device has a clutch fluid reservoir and the contents of the reservoir can very quickly become discolored because of pieces of rubber in the seals breaking down and contaminating the clutch fluid.

If you have not changed your clutch fluid in the last few months, please refer to the owner's manual for guidance on the recommended maintenance interval. Changing clutch fluid properly requires flushing the system with fresh fluid, bleeding the clutch lines as you do so, and replacing the clutch fluid with fresh fluid.

Nevertheless, if you really want to find out if your clutch seal is failing, you can also conduct a quick and dirty test using cheap clutch fluid as a quick and dirty test:

  • Using something like a turkey baster or something else, suction out the old clutch fluid from the oil reservoir.
  • Make sure that the reservoir is filled with fresh fluid by topping it off.
  • Watch the new fluid for a couple of days to see if it darkens.
  • There is a high likelihood that your fluid will turn dark within a couple of days, especially if you exhibit any of the other symptoms listed above along with the darkening of your fluid.

Clutch Master Cylinder Replacement Cost

You can usually replace the clutch master cylinder of your vehicle for a relatively cheap and simple price, depending on the vehicle. There is even the possibility of most home mechanics handling this task on their own without any help from a professional. Most vehicles require only that the clutch master cylinder be replaced, the clutch line be undone, and the master cylinder be removed from the firewall, then the new unit is installed (reverse the procedure).

Depending on where you live, you may be able to get a clutch master cylinder replaced by a professional for somewhere between $180 and $420. In most cases, parts will cost between $100 and $300. You should be able to replace the cylinder in less than an hour, so in most cases, you should expect to pay between $80 and $120 for labor depending upon the severity of the problem.

Generally, it is recommended to change both the clutch slave cylinder as well as the clutch master cylinder at the same time. In most instances, if one of these parts fails, it is likely that the other part will follow suit within a short period of time as well.

Rebuilding clutch master cylinders can save money. There is a rule of thumb that most units should be bench-bled before installation. In the event that the clutch master cylinder needs to be replaced, the clutch pedal will likely need to be adjusted. The manufacturer's manual of your specific vehicle can provide you with more detailed information about your vehicle. 

Are you interested in learning more about cars and their maintenance? Head over to the KeepDriving website and check out our blog post about the P0300 diagnostic trouble code.

Founder, Editor-in-Chief Carmelo Pickel is the Founder and Editor-in-Chief of Keep Driving, with almost 20 years of experience working in the industry. Before founding Keep Driving, Carmelo held leadership roles for over a decade on top automotive dealership corporations across North America, handling various leadership roles in Sales, Marketing, and Incentives.
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