(Updated on July 28, 2022)
The clutch master cylinder is an important component in vehicles with manual transmissions. When you apply pressure to the clutch pedal, it separates the drive wheels from the engine so that you can change gears.
The clutch would not be able to perform this function if it weren’t for the hydraulic pressure created by the clutch master cylinder. That is why if something were to ever happen to the clutch master cylinder, it would greatly impact your ability to change gears or drive the car in general.
What is a Clutch Master Cylinder?
In a hydraulic clutch system, the clutch master cylinder pushes clutch fluid down to the slave cylinder. The slave cylinder then presses on the clutch fork, which acts as a lever that separates the pressure plate from the flywheel.
This process disconnects the engine from the driveline. Most modern vehicles use a hydraulic clutch.
The Top Symptoms of a Bad Clutch Master Cylinder
To understand when the clutch master cylinder in your vehicle is starting to go bad, there are certain signs that you can recognize which could help you diagnose the issue. Below are the top symptoms of a bad clutch master cylinder.
1) Strange Noises
When you go to shift gears or apply pressure to the clutch pedal, do you hear any weird sounds? If you do, this could be an early warning sign that your clutch master cylinder is going bad.
The noises will often become louder or more frequent as the cylinder condition gets worse. Don’t let them get too much louder if you already notice them. It’s best to figure out what’s causing the problem, then replace the component that has gone bad.
Strange noises when you press the clutch pedal could also be caused by other components in the transmission going bad, such as the pressure plate or throw out bearing.
2) Shifting Problems
Whenever you have a damaged or worn out clutch master cylinder, it may not be able to generate the hydraulic pressure needed to shift the transmission properly. Perhaps there is a leak inside of the cylinder that is causing this to happen.
As a result, you won’t be able to fully disengage the clutch when you apply pressure to the clutch pedal.
Does your transmission grind or take significant effort to shift into any gear? This could be a sign that there is a problem with your clutch master cylinder. These issues may also arise when you have a bad slave cylinder.
Bleed the Clutch Lines
If you experience difficulty shifting, one of the first things you should try is to bleed the clutch system. Sometimes this involves bench bleeding either the master or slave cylinders, particularly if you bought a new unit and it was dry inside.
Bench bleeding may be required when a master or slave cylinder is positioned such that the bleeder screw is not the highest point on the unit while the car is sitting on level ground. This is because air can be trapped with no way out at the top of the part.
3) Low Resistance in the Clutch
There should always be a little bit of resistance when you step on the clutch pedal. If the clutch pedal feels too soft or spongy as you apply pressure to it, then there could be a leak in your clutch master cylinder.
In a lot of these cases, the seals inside the master cylinder are responsible for the leak. You can try to repair these seals, but it is sometimes easier or more cost effective to just replace the entire clutch master cylinder.
4) Clutch Falls to the Floor
Does the clutch pedal fall right to the bottom of the floor after you step on it? Whether it goes all the way to the bottom or sinks past its resting point, this is a sign that the clutch is not receiving enough hydraulic pressure. This symptom could happen once your clutch master cylinder has completely died.
5) Dirty Clutch Fluid
Check the clutch fluid reservoir to see the condition of the clutch fluid. If the fluid looks dark, dirty, or there isn’t enough fluid in the reservoir, then it could cause problems for your clutch master cylinder.
The clutch master cylinder may get dirty if its inner seals are damaged or worn out, causing contamination of the fluid. This commonly takes place as the seals’ age and get older.
You will also get low fluid levels once the clutch master cylinder starts leaking, too. As soon as you notice dirty fluid, replace your clutch fluid. If the new fluid gets dirty quickly, you may want to consider replacing the clutch master cylinder as well.
Clutch Master Cylinder Replacement Cost
Most clutch master cylinders are fairly cheap and easy to replace. The average clutch master cylinder costs about $100 for the part, +/- $50 depending on your vehicle. Adding on an hour or two for labor will bring you to roughly $300.
This is typically an easy job for a home mechanic, particularly on vehicles that are easy to work on. If you replace the clutch master cylinder, make sure you bleed the clutch system. Replacing this part introduces air into the clutch lines, and the car won’t shift right until the system is bled.