How to Bleed a Hydraulic Clutch
If you’re having trouble with your hydraulic clutch releasing—that is, when you try to shift with the clutch all the way in, it feels like the car still “wants” to be in gear—there’s a good chance you may have air in the system. Air trapped within the system defeats the mechanical advantage of hydraulic pressure—the air can be compressed much more than the fluid, so when you step on the pedal, the clutch itself is not fully activated.
That’s the bad news. The good news is that this is a problem that may often be fixed simply by adding fluid and bleeding the system, and you’re about to learn how to do just that.
Step 1 – Check Fluid Level
Check the level of the fluid in the reserve reservoir. Your owner’s manual will show you where this is, though it is often in the rear of the engine compartment, closest to the driver. Add as much fluid as necessary to reach the “full” level.
Throughout the process, either you or your assistant must remember to check the fluid level regularly during this process. If the reservoir reaches empty, the system will begin taking more air in, adding to the problem you’re already trying to solve.
Step 2 – Depress and Hold the Clutch Pedal
While the bleeder screw is still tight, place the pan underneath the bleeder screw fitting. Have your assistant pump the clutch pedal gently several times, and then depress the pedal all the way to the floor and hold it (it is very important to know that releasing the pedal early could result in air being sucked into the system via the bleeder valve).
Step 3 – Open the Bleeder Screw
With the wrench, slowly loosen the bleeder screw about one-half turn. A mixture of fluid and air should come out of the valve. As the flow from the screw fitting slows, re-tighten the bleeder screw until it is snug, and completely closed, but easily loosened again. At this point, your assistant can allow the clutch pedal to return to the upright position. Be sure your assistant does not allow the pedal to rise before you have re-tightened the screw, as doing so can result in more air being drawn into the system.
Repeat steps 1 to 3 several times, until no air, only fluid, comes out of the valve (it should not sputter or hiss at all). At this point, give the bleeder screw an extra quarter-turn to ensure it won’t come loose. You don’t want to over-tighten and strip either the screw or the fitting, but if the bleeder screw comes loose, you will quickly lose hydraulic fluid while driving.
Again, make sure the reservoir contains enough fluid after each round of bleeding, and again fill it to the “full” level when the process is complete.
After you’re done, test the clutch out in a driveway or parking lot before taking it to the road. If you have the time, after you’ve tested the clutch leave it parked for an hour or so with a piece of cardboard underneath the bleeder valve; this way, you can see if anything is leaking. A couple of drops is most likely nothing to worry about, as there will be residue remaining from the bleeding process, but if you find any puddles whatsoever, make sure to check that you’ve completely re-tightened the bleed valve.
And there you have it! You’ve just bled your hydraulic clutch system, and very possibly solved your problem and saved yourself a few bucks along the way!