The clutch master cylinder is a component that you’ll find in a manual transmission vehicle. Remember that manual vehicles require the driver to operate a clutch when stopping or changing speeds. The purpose of the clutch master cylinder is to generate hydraulic power which allows the clutch to function properly.
Basically, brake fluid is stored in the reservoir of the clutch master cylinder. There are hoses which connect the clutch master cylinder to the clutch slave cylinder.
As soon as you step on the clutch pedal, brake fluid in the reservoir of the clutch master cylinder starts flowing to the clutch slave cylinder. This creates the hydraulic pressure needed to activate the clutch and disengage the shafts of the engine and wheels.
If you ever notice the clutch slipping or failing to fully engage, you need to bleed the clutch master cylinder to fix this problem. This means you’re letting air “bleed” out of the cylinder.
To properly bleed the clutch master cylinder, you’ll need a partner to reduce pressure on the clutch at the appropriate time. You’ll also need more hydraulic fluid readily available.
7 Steps to Bleed a Clutch Master Cylinder
Below are the steps to bleed the clutch master cylinder.
1) Locate the Clutch Master Cylinder
The first thing you need to do is locate the clutch slave cylinder of your vehicle. If you know where your clutch master cylinder is, the clutch slave cylinder should be located to the lower right of the master cylinder.
Once you’ve found the slave cylinder, locate its bleeder valve. This should look like a small bolt which has a diameter of about 8 millimeters.
2) Open Bleeder Valve and Purge Air
Ask your partner to apply firm pressure to the clutch pedal in the cabin of your vehicle. Tell them to press down the clutch pedal all the way until it reaches the floor.
Now, you will use a wrench (usually 8mm) on the bleeder valve to loosen it up. Keep loosening the valve until air comes out. You should start seeing hydraulic fluid “bleeding” out after that. Make sure you place a container down so that the fluid can fall into it.
3) Close Bleeder Valve
Use the wrench on the bleeder valve to tighten it back up again. Have your partner slowly take pressure off the clutch pedal until it reaches its regular position. See if there is still enough fluid in the master cylinder.
If there is not, then you may have a leak somewhere like on the clutch hose or one of the cylinders. Even if there is a leak the size of a pinhole, you need to replace that part entirely.
4) Bleed Clutch Slave Cylinder
Repeat this process again by bleeding air out of the slave cylinder. Again, have your partner apply firm pressure to the clutch pedal so that it is touching the floor. Use the wrench to loosen the valve until air bleeds out.
Keep repeating this cycle of air bleeding until there is no more air coming out, but only fluid instead. At that point, close/tighten the bleeder valve.
5) Top Off Brake Fluid Reservoir
Have your partner slowly release the clutch pedal until it is returned to its normal position. Go to the master cylinder and open the top of the brake fluid reservoir. Take your extra hydraulic fluid and pour it into the reservoir until the fluid reaches the “Full” line. Try not to add so much that it overfills.
6) Test Clutch Pedal
Now just test the clutch by starting the vehicle and stepping on the clutch pedal yourself. There should be a firm feel to the clutch. Also, change gears to see if they’re smooth or slippery. If they’re smooth, then everything is fine now.
6) Clean Up
Clean your work area and all the tools and containers in it. If there is hydraulic fluid on any chrome trim or paintwork, then you need to clean it up immediately because the fluid can damage the chrome and paint.