Symptoms of Air in Clutch Line: Identifying the Signs

Knowing the symptoms of air in clutch line issues is necessary for every driver, especially if you intend to keep your clutch and brakes functioning at optimum capacity. Symptoms of Air in Clutch Line In this article, we’ll discuss all the symptoms, as well as the causes of air in the clutch line and its solutions.

What Are the Most Common Symptoms of Air in Clutch Line?

The most common symptoms of air in clutch line are a mushy clutch pedal, difficulties shifting gears, and stuck pedals. Other times, you may also experience symptoms like little or zero resistance from your clutch, reduced clutch fluid, or dark clutch fluid.
  • Soft or Mushy Pedal

A soft or mushy pedal is one of the most common symptoms of air in clutch line. Ideally, your clutch pedal should feel springy every time you press it. However, if the air is trapped inside your clutch line, it will feel mushy and soft. If you get this kind of feedback consecutively from your clutch while driving, it means there is air inside your clutch hose, and it’s making its way to the clutch slave cylinder. When you press down on the clutch pedal, hydraulic fluid is compressed and sent from the master clutch cylinder to the slave cylinder through the clutch hose or line. However, when there is air inside, it gets compressed, also. The imbalance brought about by the compressed air in the system causes that odd feeling you notice in the pedal when you engage it. Most times, in this case, the problem isn’t from holes or openings in the clutch line but from air molecules that seeped into the clutch cylinder.
  • Difficulty Shifting Gears

Difficulty changing/shifting gears in your car could indicate air in the clutch line. In a manual transmission car, the clutch temporarily disconnects your engine power from the transmission so you can switch gears without interruption. This is why a failing clutch system will always affect gear shifting.
As air enters your clutch line, it compromises the fluid inside it. This makes the fluid ineffective and makes transporting fluid to the slave cylinder difficult, causing you to experience difficulty when shifting gears. Most times, when air enters the clutch line, it’s a result of punctured holes or ruptures on the clutch hose. Often, in serious cases, your vehicle’s hydraulic fluid may leak out. If you have a leaky clutch hose, you will find it hard to shift gears like you used to. Also, you’ll hear grinding noises while shifting gears.
  • Low/Reduced Clutch Hydraulic Fluid

Low or reduced clutch hydraulic fluid is another symptom of air trapped in the clutch line. When air enters your clutch line via any punctured holes or openings, your fluid will equally leak out. Clutch hoses are made of rubber, so they easily rupture. If you find out that your hydraulic fluid doesn’t last long after it’s replenished, it’s a sign of a possible leak. Causes of Air in Clutch Problem Leaks can be dangerous if left untreated because they keep the hydraulic fluid level low. Since the hydraulic fluid is what your vehicle uses to apply pressure, this situation compromises the entire clutch system.
  • Zero Pedal Resistance

Zero pedal resistance could also indicate air in the clutch line. If you press down on the pedal and it goes right to the floor without any resistance, there’s either an air-bubble problem or a leak problem. Sometimes, it may be both. At this point, your clutch line or master hydraulic cylinder must have been drained of nearly all of the hydraulic liquid due to leakage, leaving air to fill up the empty space.
  • Frozen Pedal

A frozen or stuck pedal is another symptom of having trapped air inside your clutch line. In this case, the pedal engaging your clutch is stuck to the floor and unable to disengage. This usually happens when an opening in the master hydraulic cylinder allows air to enter and makes a substantial amount of fluid leak. A stuck pedal makes it impossible to drive your vehicle, as you’ll be unable to shift gears.
  • Clutch Engages Abnormally

If your vehicle clutch engages abnormally, it could mean that there is air in the clutch line. As a driver and car owner, you should be used to your vehicle’s clutch engagement point. However, if you notice the clutch stalling or engaging oddly, it could be that your fluid level has dropped and air has gotten into the mix. An abnormal clutch engagement will ruin your driving experience.
  • Common Causes of Air in Clutch Line

The common causes of air in clutch line are leaks in the brake system and the master cylinder. Broken seals, corrosion, or holes and ruptures from mechanical impact can cause these leaks. As fluid leaks out, air molecules enter the brake and clutch system.
  • Brake System Leaks

Brake system leaks are one of the common causes of air in clutch lines. Some cars use the same hydraulic fluid reservoir to operate both the brake and the clutch, so if this fluid is contaminated with air bubbles, it’ll also get into the clutch line when you engage the clutch. Brake system leaks can be caused by failed piston seals, worn-out brake pads and rotors, worn-out brake drums, damaged brake hoses, loose bleeder valves, and faulty ABS modules. Most times, if brake system leaks persist, your brake fluid level will go down. In this case, you may notice a puddle of fluid beneath your car or see your brake warning lights coming on. In severe cases, you may notice your brake pedal feels mushy or spongy, or it doesn’t engage the brakes at all.
  • Master Hydraulic Cylinder Leaks

Master hydraulic cylinder leaks could also be why air is trapped in your clutch line. The clutch master cylinder is the container for the brake fluid (or hydraulic fluid) that your brake and clutch systems use to function. Both brake and clutch have their own master cylinders. If the cylinder for your clutch is leaking, air will most certainly enter inside as fluid leaks out. This air then forms bubbles inside the fluid when pressure is applied to send it down the clutch line to the slave cylinder. One of the most common causes of clutch cylinder leaks is corrosion. Corrosion, in this case, usually starts from inside when water molecules contaminate the hydraulic fluid. Over time, the corrosion will eat at the cylinder until it starts leaking fluid. Broken seals in the master hydraulic cylinder can also cause leakage and allow air, dust, and debris to enter the cylinder.

How To Fix Air in Clutch Line

To fix the air in clutch line problem, you have to bleed out the air and top it off with hydraulic fluid. You can bleed out the air using a vacuum pump. Sometimes, bleeding may not work, so you’ll have to replace the master hydraulic cylinder.
  • Hydraulic Clutch Bleeding

Bleeding a clutch is the process of drawing out trapped air from the clutch. You can do this using a vacuum pump or with the help of an assistant. Your clutch reservoir shouldn’t be empty before bleeding, so it’s important to top it before starting the process. For bleeding with a vacuum pump, you need a small tube that can fit into the nipple of the bleeder valve. Open your bleeder valve, attach the tube, and use your pump to draw out the fluid inside the system. The tube should be transparent so you can see the air bubbles trapped inside the fluid as it gets sucked out. Keep pumping out fluid until you can no longer see entrapped air inside. Once there are no more bubbles coming out of the valve, remove the tube, seal the valve tightly, then take your car for a test drive. Bleeding a hydraulic clutch with a vacuum pump is simple and efficient. However, if you don’t have a pump, you can still bleed out the air, but you’ll need an assistant to help you. To bleed with an assistant, first, get a pan and place it under the bleeder valve. Confirm that your hydraulic fluid reservoir is filled to the brim and the valve is airtight. Tell your assistant to press and hold down the clutch pedal as hard as possible. Open the valve slightly to allow the fluid to flow out. The flow should stop after a few seconds as the pressure exerted from the pressed-down pedal is expelled. You should also see bubbles of air coming out. Once the flow stops, tell your assistant to release their hold on the pedal. Shut the bleeder valve and repeat the entire process until you can no longer see bubbles escaping. Finally, top up your hydraulic fluid and give your car a test drive. If you do it correctly, your pedal should feel firmer.
  • Replace Master Cylinder

In some cases, bleeding the clutch will not suffice; you’ll have to replace the master hydraulic cylinder. This is usually necessary when your cylinder is leaking or has broken seals that will allow air to enter even after bleeding. The clutch master cylinder can be found on the engine bulkhead in front of the brake pedal and next to the brake cylinder. Removing Clutch Line Air To replace the clutch master hydraulic cylinder, first, remove the hydraulic line from the cylinder (don’t bend the line, or else it will break). Next, remove the cotter pin and anchor pin from the cylinder push rod and undo the nuts holding the cylinder in place. Finally, take out the cylinder. Now you can install the new cylinder and reattach the hydraulic line. When installing the new cylinder, ensure the push rods, pins, and hose are perfectly mounted/positioned. Any mistakes here could make your clutch fail when engaged. Also, don’t mistake the slave cylinder for the master hydraulic cylinder. Slave cylinders are usually located at the end of the clutch system, on the inside or outside of the transmission.

Check the Brake System for Leaks and Fix

Fixing leaks in your brake system could stop air from entering the reservoir and, consequently, the clutch line. You could start by checking your brake hose, pads, rotors, and drums to see if there are any damages. Also, check the reservoir. If you can’t find anything, press hard on the brakes and check again. Doing this will force out fluid through any tiny leakage points, making it easy to spot. Once you find the damaged part, replace it and top up the hydraulic fluid.


– How Long Should a Master Hydraulic Cylinder Last?

A master hydraulic cylinder should last for about 60,000 to 200,000 miles. However, this number varies depending on the manufacturer of your vehicle. Frequent usage of your clutch and brakes also subjects your master hydraulic cylinder to wear and tear and reduces its lifespan.

– What Are the Signs and Symptoms of a Bad Clutch?

The signs and symptoms of a bad clutch include a soft or sinking pedal, a spongy clutch pedal, grinding noises while engaging the clutch, burning smells, and difficulty changing gears. You may also notice that it takes higher RPMs for your car to attain certain speeds than usual.

– How Much Will You Spend To Change Your Clutch?

You will spend between $750 and $2,500 to change your clutch. The actual price will depend on the car model and the mechanic or auto shop you employ for the job. Mechanics usually charge more for changing front wheel drives and when other car clutch components are damaged. Spongy Clutch Pedal  

Can Air in the Clutch Line Cause a Charging System Failure?

Air in the clutch line can cause a variety of issues, but a charging system failure is not one of them. While fixing charging system failures is crucial to maintaining proper battery function, it is not directly related to the presence of air in the clutch line. It’s important to address each issue separately to ensure optimal performance and safety.


Having air in your clutch line can make driving difficult, especially when changing gears. If you realize you have this problem in your car, attend to it quickly, or your clutch system may fail completely. Let’s go over the main points of this article one more time:
  • The symptoms of air in clutch line include soft or mushy pedal, gear-changing difficulty, stuck pedals, and reduced clutch fluid.
  • You may also notice your clutch engages abnormally or has zero resistance.
  • The two main causes of this problem are master cylinder leaks and brake system leaks.
  • To fix this problem, you need to bleed out the air from the cylinder using a vacuum tube or with the help of an assistant.
  • Replacing the master hydraulic cylinder and fixing brake system leaks can also solve this problem.
Changing the hydraulic cylinder or fixing brake system leaks can be tricky, so see a mechanic if you’re not sure how to go about it.
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