Auto Repair Q&A



Cooling System










Auto Repair Products

Bleeding a Clutch Master Cylinder

Clutch master cylinder

After talking about replacing a clutch master cylinder last week, we mentioned the need to bleed the new master cylinder once installed. This also coincides with an interesting problem from a forum user and his 1992 Toyota Tercel.

There are two ways to bleed the clutch on a car: standard and power bleeding. Standard bleeding is much like bleeding the brakes, with one person controlling the flow from the bleeder valve on the clutch master cylinder and the other pumping the clutch pedal. Power bleeding uses pressurized fluid going into the system, pushing air out ahead of it. Both methods can work, though power bleeding tends to be more likely to do a complete job of clearing the system of air.

Standard Clutch Bleeding

To start, be sure the system is sealed (all valves are closed, connections tight) and that the reservoir for the clutch master cylinder is full of fluid. You'll need at least another quart of fluid on hand plus appropriate wrenches or screwdrivers to open the bleeder valve. A container to capture bleeding fluid and a tube to run from the valve into the bottom of that container are also needed.

Simply put the hose on the bottom of the bleeder valve and run it into the catch container. Fill the catch container partially with clutch fluid until it's above the bottom of the hose from the bleeder.

Have a friend ready to slowly pump the clutch pedal in the car as you bleed it. Open the bleeder valve slowly and signal your friend to begin alternately pressing and releasing the clutch pedal. Watch for air bubbles coming up from the hose in the catch container as the pedal is pressed inward. Having fluid in the container keeps any back-pressure from sucking air back into the clutch M/C.

Periodically check the master cylinder's reservoir and refill as needed. Do not let it get below the "fill" line. When bubbles stop appearing in the catch container as the clutch pedal is pressed, close off the bleeder valve and test the clutch a few times.

Repeat this process as necessary until the bleed is complete and the clutch operates as it should.

Power Bleeding

Using a power bleeding system on the clutch master cylinder is similar to and uses the same tools as those used for brake bleeding. Procedures are basically the same as well.

Use the instructions on your power bleeding kit, which usually will attach to the resrvoir's top and have either a built-in pump or air hose attachment to use shop air to build pressure in the bleed kit. Most run in the 10-20 psi range.

These kits work by pressurizing fluid and forcing it into the system, which pushes air out through the bleeder. See above instructions for the other half of the setup or follow the instructions that came with your bleeder kit. Because a power bleeder is under pressure, filling the catch container to prevent reverse flow is not necessary.