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 Sacramento Valley MG Car Club

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Bleeding Your Clutch Hydraulic System

We have received many calls from owners of British cars who have rebuilt their clutch hydraulic system, replaced the slave cylinder hose, or even the whole system, and still had a very soft pedal that would not release the clutch sufficiently to allow silent engagement of first gear. Eventually they had their British car specialist fix It. What did he do that they didn't? He correctly bled the hydraulic system.

The reason to bleed any hydraulic system is to remove all the air bubbles from the system. Liquids, such as brake/clutch fluid, for all intents and purposes, are not compressible. However, if there is air in the system, it will compress or become smaller, when the pedal is pressed. The pedal will feel soft. moving without moving the piston In the slave cylinder enough to allow release of the clutch disc.

Where is the air in the system and how do we get It out? Air in the hydraulic system will always go to the highest point. In this case, it would be stuck In the highest point of the pipe between the master cylinder and the slave cylinder. Bleed the hydraulic system in the usual way with a hose fitted to the bleed screw on the slave cylinder and immersed in brake Auld in a clean container.

After you have moved about half pint of Girling brake Auld (do not use anything else) through the system, release the clutch pedal. Then close the bleed screw and use the rod on the front of the slave cylinder to push the piston back into the cylinder. This will cause the bubbles in the highest point of the pipe to be pushed back into the master cylinder and out of your hydraulic system Into the atmospere. Wait a few seconds. You should now have a firm pedal. If not. push the slave cylinder piston back Into the body without bleeding the system again.

Norman Nock