A clutch master cylinder is a part of many cars with a manual transmission. It provides the hydraulics for the clutch. If you start to feel or hear something unusual when you shift gears or press the clutch pedal down, pay attention because it may signal a problem with your master cylinder. If you have a bad clutch master cylinder then you will probably see some of these symptoms. Keep in mind, these symptoms can be the result of other problems within the transmission as well but they are good to look for if you suspect a master cylinder issue.
1. Soft Pedal
A “soft” pedal is when you can feel with your foot that the pedal has lost some its normal resistance as you press it down. This can be due to a leak in the master cylinder or the slave cylinder. The leak may be due to a problem with the seals.
2. Hard to Shift
If it is difficult to shift gears this is a sign that the master cylinder is failing. When you cannot depress the clutch properly it can be difficult to change gears.
3. Pedal Stuck to the Floor
If your clutch pedal will not raise off the floor, then the hydraulics to the clutch are not working at all. Most likely the master cylinder has gone out and will need to be replaced immediately. You cannot drive the car in this condition.
4. Low Fluid
If you find that the clutch fluid is low and you have to refill it more often than normal then you probably have a leak. This leak may be coming from the master cylinder. It could also be a crack or hole anywhere in the clutch system. All parts of the clutch hydraulics should be checked for leaks to isolate the problem.
5. Fluid Rise in the Reservoir
If you have a bad master cylinder then you can do the following test with the help of an assistant. Have your assistant press down on the clutch while you look to see if the clutch fluid in the reservoir rises when the clutch is down and then rises again when the clutch is released. If it does then your master cylinder needs to be replaced.
6. Noisy Engagement
If you are at a light with the brake on and the car in gear you may hear a loud noise as you hold down the clutch pedal. The cause of this may be that the master cylinder is leaking and won’t hold the release fork when the pedal is pressed down.
7. Fluid on the Cylinder
If you still aren't sure what the problem is then take a look under the hood, and examine the master cylinder itself. If the bottom of the cylinder feels wet then the leak is probably coming from the master cylinder.
A failing clutch master cylinder will lose its power to maintain the hydraulic pressure needed for the clutch to function. Taking care of repairs to the cylinder will protect you from damaging your whole transmission, so be sure to have it repaired right away.