Bleeding a hydraulic clutch is about removing the air and any old brake fluid from the system to get it working properly. To do this, you’ve got to get rid of any air that’s trapped in the hydraulic clutch system – that’s the bit that connects the clutch pedal to the gearbox via the master and slave cylinders. Air in the system stops the fluid pressure from getting through properly, which makes it hard to completely disengage the clutch and can make gear changes a real pain. Proper bleeding makes sure you get a smooth gear change and prevents all sorts of clutch problems down the line. This guide is aimed at vehicle owners and DIY enthusiasts who want to keep their hydraulic clutch system in good nick – and that means regular maintenance of the master cylinder and slave cylinder to keep things running smoothly.
Tools and materials required for the job
If you want to successfully bleed your hydraulic clutch, you’ll need the following tools and materials on hand:
- The correct type of brake fluid (check your vehicle’s manual for the right one)
- A spanner or wrench will come in handy
- Some clear tubing to keep an eye on any air bubbles
- A bit of flexible tubing to hook up to the bleeder valve
- A container to catch the old brake fluid
- A pan to catch any fluid that leaks out – just in case
- An assistant to lend a hand (optional)
- Some gloves and a few cloths for cleaning up
Before you get started, check your vehicle’s manual to make sure you’ve got the right type of brake fluid.
What to look out for
So what are the signs that’ll tell you your hydraulic clutch needs bleeding?
- A soft or spongy clutch pedal – it’s all too common to have a pedal that feels like it’s got a bit of give in it\
- Difficulty changing gear\
- Clutch not disengaging properly\
- Pedal feel is all over the place
If you notice any of these symptoms, get your tools ready before you start.
Bleeding a Hydraulic Clutch: Step by Step
1. Find the master and slave cylinders
First off, locate the hydraulic clutch reservoir and the bleeder valve. That’s the bit that’s usually near the brake master cylinder in the engine bay, and the bleeder valve or screw or nipple on the slave cylinder body. The key thing to remember is that the bleeder screw should always be at the top of the slave cylinder body to get all the air out of the system. If it’s not at the top, you might have to reposition the slave cylinder or switch the bleeder screw to the top port, if that’s possible.
2. Check and top up the fluid reservoir
Before you start bleeding that clutch, check the fluid level in the master cylinder reservoir. If it’s low, top it up with the correct type of brake fluid. Don’t forget to replace the cap afterwards to stop air getting in – or any other nasties, for that matter.
3. Hook up the hose to the bleed valve
- And make sure it’s submerged in the container
Take a length of clear or flexible tubing and attach one end to the bleeder valve or nipple on the slave cylinder. Make sure the connection is nice and secure, so no air gets in. Then, submerge the other end in a pan or a container to catch all that expelled brake fluid. This way, you can keep an eye on the air bubbles and keep your workspace nice and tidy.
4. Pump the clutch pedal
Give the system a bit of a push
Get someone to push the clutch pedal all the way down and hold it there. What you’re doing is building up pressure in the clutch system, so have a few goes to get some pressure built up before you open the bleeder valve.
5. Open the bleed valve
- Get the old fluid and air out
Now locate that bleeder valve – it’s probably a screw on the slave cylinder. Take a clear tube, hook it over the bleed screw, and submerge the other end in a container with brake fluid. Open the screw just a tiny bit, and let the old fluid and air come out. When things settle down and only fluid is coming out, close the screw up again. Don’t forget to tighten it to the right torque – you don’t want to over-tighten it and damage the screw or the seal.
Repeat the whole process until there are no more air bubbles coming out.
6. Tighten the valve and let go of the pedal
To prevent air from sneaking back into the system, make sure you close that bleed valve before letting go of the clutch pedal. You might need to use one hand to fiddle with the valve while the other hand wrestles with the pedal, all while keeping a watchful eye out for any air that might be trying to seep back in through the hydraulic line.
7. Repeat the process
Repeat the routine of pressing the clutch pedal down, then letting it go, and opening and closing the bleeder screw until you see no more air bubbles in the fluid. If you’re flying solo, you can use a zip tie to hold the pedal down for you while you work on the bleeder screw.
If you’re having a tough time getting the air out of the system, or you notice it keeps coming back, check that the bleeder screw is in the right spot – it should be positioned at the highest point of the slave cylinder. If it’s not, you might be making things harder on yourself and potentially need to replace or reposition the slave cylinder to get the air out for good.
8. Keep an eye on the fluid level
Don’t let the reservoir run dry during the bleeding process – that’s key. Always check the level of the fluid in your master cylinder and make sure you’re topping it off to the recommended fill line with the right hydraulic fluid for your vehicle. And don’t forget to check your vehicle’s manual for the correct type of fluid to use and to keep an eye on the level as you go.
9. Test the clutch pedal with a firm hand
- Check the firmness and engagement
After you’ve bled the hydraulic clutch, press the clutch pedal all the way down to the floor. It should feel firm down there, not all spongy and squishy. If it feels spongy or soft, there’s probably still air trapped in the system. And a spongy clutch can make shifting gears a real pain. Give it a try by shifting gears – if you can’t change gears smoothly or the pedal still feels spongy, you probably need to go back and bleed it some more until the pedal feels firm and you can shift gears without a problem.
The process is done when all you see coming out of the bleeder valve is fluid, with no air bubbles in sight.
Now that you’ve completed these steps, you might want to look into some alternative methods for bleeding a hydraulic clutch if needed.
Alternative bleeding methods to try
There are a few different ways to bleed a hydraulic clutch, including using a manual/helper, gravity/vacuum, and reverse bleeding.
The three main ways to bleed a hydraulic clutch are:
- Manual/helper method
- Gravity/vacuum method
- Reverse bleeding
Gravity bleeding
When to use this
Gravity bleeding, or gravity bleeding if you will, is a pretty simple way to get the air out of a hydraulic clutch system. What you do is open the bleeder valve and let gravity do its thing – let it pull the brake fluid through the system without pressing the clutch pedal. This relies on gravity feed, where the fluid flows down from the reservoir through the lines and out the bleeder valve, taking air bubbles with it.
Gravity bleeding is a good option when you’ve got the time, and you just don’t want to make a big fuss about it. It works well if the bleeder screw is at the top of the slave cylinder, letting gravity do its job and get the air out. But if the screw is at the bottom, it might not work as well – air might not escape as easily, and you might need to adjust the orientation or swap the ports to get the air out properly.
Pros and cons of gravity bleeding
The main advantage of gravity bleeding is that it’s easy – no special tools or helpers needed. And it’s less likely to introduce new air into the system, which is a plus. However, it can be pretty slow, and if the slave cylinder or bleeder valve is not set up in the right way for gravity feed, air might still be trapped. This method might not be the best choice for systems that are a bit more complicated, or if the bleeder screw is not in the right spot.
Vacuum bleeding
- Faster and more controlled
- Requires a vacuum tool
- Using a speed bleeder with a vacuum tool lets you get the job done a lot more quickly and efficiently, since the speed bleeder helps prevent air from sneaking back into the system during the process.
Pressure bleeding
- Best for getting consistent results
- Typically used in workshops
This section differentiates you.
If you want to avoid common mistakes, take a gander at the next section before you start your project.
Common mistakes to avoid
- Don’t let the reservoir run dry
- Not tightening the bleed valve properly: Always make sure to tighten the bleed valve up to the correct torque so you get a good seal. If you don’t, air might get back in, or you could end up with leaks.
- Using the wrong brake fluid is a real no-no: Always make sure to use the fluid that your vehicle manufacturer says to use. The only difference between brake fluid and clutch fluid is the system they’re meant for, so using the wrong one can mess up seals or reduce performance.
- Releasing the pedal while the valve is still open
- Not checking for leaks
If you run into any problems during the process, you can check out the troubleshooting section below.
Troubleshooting – Clutch still feels spongy
- Air is still in the system
Clutch pedal still feels spongy after bleeding? That probably means there’s still air trapped in the system. This can cause some real problems with shifting gears, so you’ll probably need to go back and try bleeding it some more to get all the air out.* Repeat the bleeding process
If the clutch pedal still feels spongy after bleeding, do another round until the pedal feels firm, responsive and really engaging now.
Not getting any pedal pressure
- That master slave cylinder might be the problem
No fluid is coming out when you try to bleed it
- The line or valve is most likely clogged
If no fluid comes out when you try to bleed a hydraulic clutch, it’s probably because the hydraulic line, bleed screw or nipple is blocked. Either dirt has clogged the line, or the bleeder nipple is blocked. Check that the bleeder screw or nipple is fully open and positioned higher than the slave cylinder to let air and fluid escape properly. If you suspect a blockage, just take out the screw or nipple and see if there’s any debris there. Continue from there.
Clutch not engaging properly, even after bleeding
- There could be a mechanical problem
If your clutch still won’t engage after you bleed the hydraulic clutch, and it’s not just a matter of air trapped in the system, there might be a mechanical fault. The slave piston, the push rod, or even the way the pistons move in the master or slave cylinder might be involved in that. Check on the state of those parts and look for signs of wear or damage. For example, if the slave piston is stuck or the rod is not properly fitted, air may stay trapped or the clutch wont disengage properly.
If you’ve sorted your issue out, take a minute to review these safety tips before finishing up.
Safety tips
- Be careful not to spill brake fluid on your paint
- Put on some gloves
- Dispose of old fluid responsibly
- Make sure you are working on a solid surface
Conclusion
- So your clutch is working properly again
- Don’t forget to do regular maintenance
- Optional: think about calling a pro if the problem persists
FAQs
Can I bleed the clutch by myself
Yes, you can bleed a clutch by yourself using a one-man bleeder kit or a vacuum pump. These tools make it possible to draw fluid through the system and get rid of air without needing someone to press the clutch pedal for you.
How long will it take to bleed the clutch
Bleeding a hydraulic clutch usually takes about 15 to 30 minutes depending on how experienced you are and the tools you use. If there are stubborn air bubbles involved, it might take a bit longer.
Is clutch fluid the same as brake fluid
Yes, clutch fluid and brake fluid are actually the same (both usually use DOT 3 or DOT 4) – the only difference being that clutch fluid is used in the clutch system, and brake fluid is used in the braking system.
How often should you bleed the clutch
Its recommended to bleed a hydraulic clutch system every two to three years, and also whenever you do clutch or transmission maintenance, to keep it running smoothly and avoid issues caused by trapped air or moisture in the system.