how to bleed a hydraulic clutch

How to Bleed a Hydraulic Clutch

There are three methods used by auto manufacturers to actuate the clutch diaphragm in manual transmission vehicles: push rod, cable, and hydraulic. Adjusting push rod and cable-type linkages is fairly simple, but hydraulic clutches require bleeding when installing a new hydraulic throwout bearing. Here’s what you need to know about how to bleed a hydraulic clutch.

Clutch Actuators Types

There are two types of hydraulic clutch actuators: the ram type and the bearing-type.

Ram-type clutch actuators

This system is a hybrid of a push-rod mechanism, where it uses a typical mechanical clutch fork and throwout bearing to operate the clutch diaphragm. The push rod linkage is replaced with a hydraulic system, where the pedal operates a master cylinder which drives a slave cylinder mounted outside the bellhousing. The slave cylinder or ram, moves the clutch fork, operating the clutch engagement.

Bearing-type clutch actuators

Most modern vehicles have gone to the fully-integrated hydraulic system, which eliminates the mechanical fork and bearing and replaces it with a hydraulic throwout bearing. When the clutch master cylinder pressurizes the fluid in the lines, the bearing ram expands, pushing on the clutch diaphragm, disengaging the clutch.

This is a hydraulic bearing. Most of these units have two lines- one goes to the master cylinder, the other is the bleed line. The bearing rides on a stub that goes around the input shaft of the transmission.

This is a hydraulic bearing. Most of these units have two lines- one goes to the master cylinder, the other is the bleed line. The bearing rides on a stub that goes around the input shaft of the transmission.

 

This hydraulic bearing, from a 2009 Dodge Challenger, is a self-bleeding unit. When replacing it or if the master goes dry, you simply pump the pedal to bleed it. 100 to 200 times. yes, seriously.

This hydraulic bearing, from a 2009 Dodge Challenger, is a self-bleeding unit. When replacing it or if the master goes dry, you simply pump the pedal to bleed it. 100 to 200 times. yes, seriously.

Bleeding the clutch

Bleeding the clutch is a little different from bleeding brakes. The main difference is that there is only point where the fluid is utilized, so air is less likely to be trapped in a T-fitting or caliper. Because of this, the process is very simple and can be handled by one person.

Start off with plenty of fluid in the reservoir. You don’t want the master to run dry, which would cause more headaches.

Always start with the reservoir topped off. You will lose some fluid during this process, keep an eye on the level.

Always start with the reservoir topped off. You will lose some fluid during this process, keep an eye on the level.

Locate the bleed port on the ram or the line coming off the hydraulic bearing. If you are working with a bearing, you will need two wrenches, one to hold the line and one to open the bleeder.

The bleed line is often hanging loose, so you need two wrenches, one to hold the fitting and one to operate the bleeder.

The bleed line is often hanging loose, so you need two wrenches, one to hold the fitting and one to operate the bleeder.

Crack the bleeder open and let it drip. Because the fluid is above the master cylinder and the lowest point in the system is the bleeder, it should push all of the air out of the lines and out of the ram or bearing. If this is a new system, you will get a few drops slowly and the speed will increase as the air is expelled until the fluid is consistently dripping. Close the bleeder screw, and top off the reservoir.

Just let it drip. This is called gravity bleeding. It can take a while, but most of the air will come out naturally.

Just let it drip. This is called gravity bleeding. It can take a while, but most of the air will come out naturally.

Now you can check the clutch pedal. It should be firm, not spongy and it should not change with repeated pumping. If it gets more firm or feels spongy, you need to continue the process.

After the line was gravity bled, you can check the feel. If it is still spongy, repeat the process, but this time, have a helper pump and hold the clutch pedal before cracking the bleeder open, just like bleeding brakes.

After the line was gravity bled, you can check the feel. If it is still spongy, repeat the process, but this time, have a helper pump and hold the clutch pedal before cracking the bleeder open, just like bleeding brakes.

Sometimes it may be necessary to pressure bleed the system, which is just like bleeding brakes. This involves a second person pressurizing the clutch system and holding the pedal, then cracking the bleeder open. This can be required if the ram or bearing have been disassembled.

With a little patience, you should be able to get your clutch operating at full power with a properly bled hydraulic system. Be sure to use the correct fluid in your clutch system as per the vehicle manufacturer’s specifications.

Check out all the drivetrain parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to bleed a hydraulic clutch, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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