Bleeding Your Hydraulic Clutch

Bleeding your hydraulic clutch is one of those simple jobs that can turn into a frustrating nightmare. The aim is to remove all the compressible air from the clutch system and to replace it with incompressible fluid.

I am not the one who likes doing all the mechanic work. But my professional mechanic friend Andy Hanmer finds nothing more rewarding than listening to classical music while fiddling on dirt bikes. Read on and find out how he does this job quickly and easily.

Diagnosis

When would you want to bleed your hydraulic clutch? When air is introduced to the system. Basically there are 2 ways for that to happen. 1) Crash: If the bike lands upside down (that happens sometimes ;-), and the clutch lever is then pulled in. The clutch starts dragging, or won’t release at all. 2) Maintenance: perhaps the bike is an older one or you are replacing all the fluids as part of a maintenance program. Maybe the rubbers in the master cylinder have been replaced.

In all of these cases, the hydraulic clutch will have to be bled.


Cautions!!

  • Some hydraulic clutch systems require a mineral oil and some take brake fluid. Ensure that you know which to use, as the fluids are not compatible. Generally the top of the master cylinder will have a notation, but if the top has been replaced by an aftermarket item, you will have to check the user manual.
  • Note that cleanliness is essential around clutch systems. A grain of sand can quickly damage seals and surfaces.
  • Note also the brake fluid is a really good paint remover. Keep it away from painted surfaces.
  • Finally, brake fluid is hygroscopic, and will absorb water from the atmosphere, keep the container closed when not using it.


Building A Bleeder

Take a 20cc syringe, remove the plunger and clean up the barrel. Fit a piece of clear silicon pipe that was the correct size to the nozzle of the syringe to fit over the bleed nipple on top of the clutch slave cylinder. (The slave cylinder sits between the front sprocket and ignition cover, the master cylinder is what the clutch lever is connected to)

In the top of the syringe bore a hole and insert a piece of wire which is then strung from the handlebars to keep the tool vertical.

Bleeding

The top of the master cylinder must be removed. Inside the master cylinder you will find a round white plastic protector. This must be gently pried off and removed temporarily. It can trap a bubble of air which then bobs in and out of the system and prevents a proper bleed.

Pop the rubber cover off the bleed nipple, fit the appropriate ring spanner to the nipple, and fit the bleeding tool to the nipple. Put a couple of ml of fluid into the syringe.

Fill the master cylinder to the brim. You may want to move the clutch perch on the handlebar to get the master cylinder reservoir as level as possible.

Open the bleed nipple, just over a quarter of a turn will do. Now, start pumping the clutch lever. You will see that bubbles are expelled into the syringe when you squeeze, and clear fluid is drawn into the system when you release. With this devise, there is no need to close the bleed nipple shut when you release the lever. Keep topping up the master cylinder as you pump. At some stage you will see that no more air is coming out of the system. Close the bleed nipple, and check the feel at the clutch lever. If it feels good, you can start closing up the system.

Closing up

With clean fingers, fit the round plastic protector back into its recess in the master cylinder, ensure that the master cylinder is full and screw the cap home. Check that the nipple is tight, and the rubber protector is in place and you’re done.

Test Riding

When test riding, you should remember that the hydraulic clutch will drag if the transmission oil is cold, so get the bike good and hot before you test. With the bike at idle, pull in the clutch and select first. If the bike moves forward and stalls, either your clutch is dragging or the clutch lever adjustment is out. Check that the free play of the lever is within spec according to your user manual, and try again. Still dragging? Do the job again. You’ll get it right eventually.

Ride safe and keep the rubber side down!

Return from HYDRAULIC CLUTCH to MOTORCYCLE MAINTENANCE




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