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9 May 2024 How to bleed a clutch: master & slave cylinder
Bleeding the car clutch master cylinder and slave cylinder is relatively straightforward. It usually involves releasing the fluid bit by bit and pumping it out using the clutch pedal to remove the air. However, other potential causes of clutch problems, such as leaks or excessive wear, should be ruled out first before you bleed the clutch.
Common symptoms of air in the clutch lines:
- A spongy or soft pedal
- Slipping gears or difficulty changing gears
- Changes in the clutch biting point
- Difficulty engaging the system
Сlutch bleeding: Why is it important?
It’s important to bleed the clutch if air gets trapped inside the cylinders or hydraulic system because this can prevent the clutch from engaging fully, leading to gear shifting problems and frequent stalling.
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Bleeding the clutch simply means removing the air bubbles inside the hydraulic system by draining some of the fluid. Depending on the situation, the best way to bleed the clutch is to either release the fluid manually or using a vacuum or pressure bleeder.
How to bleed a clutch master or slave cylinder
Before you start, you’ll need to prepare the right сar jack, vacuum pump, protective gloves, etc. Carefully read through the vehicle owner’s/repair manual and locate both cylinders. Most people typically start by bleeding the slave cylinder. This is usually located right next to the clutch assembly or the transmission.
Please note: during the bleeding process, the clutch should not be completely drained of fluid as this will likely cause more air to enter the tank as it is refilled.
How to bleed a clutch by yourself without a vacuum pump
Here’s a brief guideline on how to bleed a clutch without a vacuum pump:
- Locate the reservoir and assess the clutch fluid level. Top it up with fresh clutch fluid (stay within the minimum and maximum marks).
- Locate the bleeder screw and place a container directly beneath it to catch the fluid.
- Enlist a helper to press the clutch pedal. They should pump it several times, then press it down fully and hold it there.
- Use a wrench to loosen the bleeder screw slightly to let out some of the fluid and air.
- Once the flow of oil decreases and slows, retighten the bleeder screw. Next, release the clutch pedal and top up the reservoir with more fluid.
- Repeat the process if necessary. You should no longer be able to hear a hissing sound coming from the screw or detect air bubbles in the fluid.
Note: don’t forget to read the manufacturer’s instructions for your specific vehicle model.
How to bleed a clutch with a vacuum pump
- The first two steps are identical to those above. The main difference is that a pump is used rather than the clutch pedal.
- Attach the vacuum pump to the bleeder valve.
- Create a vacuum with the pump (see product instructions)
- Open the bleeder valve; inspect the old fluid and air bubbles drawn into the pump.
- Monitor fluid levels; avoid running the clutch dry.
- Repeat until clean fluid flows consistently.
- Tighten the bleeder valve.
- Test the clutch pedal by pressing it a few times.
- Check the system for leaks.
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How long does it take to bleed a clutch?
The whole bleeding process can normally take anything between 30 mins to 2 hours. This will depend on several factors, such as the complexity of the hydraulic system, how many bubbles there are, how experienced you are, and the chosen bleeding method.
How much does it cost to bleed a clutch?
The average garage prices for bleeding a car clutch system in the UK range between £80 and £110. This will largely depend on where you get it done and the make and model of the vehicle. If you do it yourself, you may only have to pay for the new fluid and equipment.
FAQ
- Do you have to bleed the clutch after a clutch replacement?
Yes, if the master or slave cylinder has been replaced or the hydraulic system has been disconnected, then you will probably need to bleed the system. This is recommended as air can enter the system during the replacement.
- Why won't my clutch bleed?
If the clutch isn’t bleeding properly, it could be due to a blocked bleeder valve, fluid leaks or contamination, or bleeding errors. Moreover, air pockets can make the bleeding process tricky. Carefully follow the manufacturer’s instructions and, if necessary, use a pressure bleeder or vacuum tool.
- Do you have to bench bleed a clutch master cylinder?
Bench bleeding the master cylinder can help speed up the bleeding process although it isn’t always necessary. It is usually recommended if you are installing a new cylinder or a whole new unit.
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