How Does A Clutch Work

High Clutch vs Low Clutch

How Does Your Clutch Work?

The question of a high clutch vs low clutch is typically linked to your clutch biting point where there are two main problems; a high and low clutch biting point. While every clutch works differently, as long you understand your car’s biting point, you’ll be fine.

Experienced drivers typically don’t use the car’s biting point because it unnecessarily wears down the clutch. However, they do use the biting point in your average everyday car situations such as parallel parking, hill starts and in slow moving traffic.

Stick around as we pin these two opposite biting points in our high clutch vs. low clutch showdown. However, before we start, here’s a quick crash course on the basics of a hydraulic clutch and the biting point.

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Basics of a hydraulic clutch

Without getting too technical about it, the hydraulic clutch is made up of the master cylinder, slave cylinder, and the clutch work. Whenever you depress the clutch, the clutch fluid in the master cylinder is displaced by its push rod and travels through a tube to the slave cylinder.

In the slave cylinder, the fork engages the diaphragm spring to disengage the clutch disc from the engine’s flywheel. This momentarily ceases the transmission of engine torque to the transmission, allowing you to change gears or come to a stop.

Whenever you release the clutch pedal, the clutch disc is gradually reconnected to your engine’s flywheel allowing the transmission of power through to the drive wheels. Which is brings us to the biting point, which is the lynchpin to our high vs. low clutch showdown?

The biting point

Now that you understand how your basic hydraulic clutch works; the biting point refers to that moment when your clutch disc engages the engine’s flywheel.

If you don’t already know, it’s typically found halfway through your clutch’s pedal travel. However, every clutch is a little different. Some cars come with a particularly high clutch biting point such as Hondas and Volvos while others have a low clutch biting point like a Corsa.

Mechanics typically have different opinions on the optimum clutch biting point, and some will even go as far as adjusting your biting point for you. As long as it works for you, there’s no need to change it; which is brings us to the meat and potatoes of our debate.

Biting point problems: High clutch vs low clutch

At the heart of this debate are the two main biting problems–a high and a low clutch biting point. Having a high clutch means that the biting point is further up in your clutch’s pedal travel when fully released.

On the other hand, having a low clutch means that the biting point is located further down of a fully depressed clutch pedal.

A high clutch biting point

Normally, having a high clutch is a reliable indicator of a clutch that’s wearing down or worn-out and may need to be replaced. Having a high clutch after a few years of regular use is pretty normal, but that’s if it is higher than when you first got your car.

Some of the other symptoms of a worn out clutch include having a sticky clutch while using clutch control in slow-moving traffic as well as having trouble shifting into the reverse gear. Having a high clutch doesn’t give you much room for errors and can be a pain in urban areas.

The clutch starts to slip

Getting a high bite point after a few years of use means your clutch is probably burned out, i.e., the high-friction material on the clutch disk has been used up. As the friction coating gets thinner, the pressure plate slowly loses its grip, and that’s when your car starts to slip.

While the pressure plate and flywheel may start wearing down, they typically do this much slower compared to the high-friction coating on the clutch disc — the high-friction padding on the clutch discs works similarly to the friction material in brakes.

That being said, you can consider a burnt-out clutch to be a self-feeding contraption that only wears out when it’s engaged or disengaged. As it engages the pressure plate and flywheel, the high-friction coating slips past the clutch’s metal faces, which consequently generates heat.

Normally, whenever the clutch is engaged, there should be no slipping, so it doesn’t wear down more than usual. However, when your clutch starts to slip while it’s engaged, it wears down much faster.

It slips more and more until it gets to the point where you have a non-functional clutch which will need to be replaced. It’s worth noting that nowadays, hydraulic actuated clutch systems are designed to be self-adjusting, so their clutch biting point typically doesn’t change like a mechanical linkage clutch.

However, the main issue is that when they burn-out, they’re gone, and this happens very quickly after you start having a high clutch. And once your clutch starts slipping there’s no telling how long it will last.

How long a worn out clutch will last

That being said, the biggest factor that determines how long a wearing down clutch will last, depend on how often you ride the clutch and how often you race-start. If you notice your clutch has started to slip or has a different feel to it, then it’s probably a sign that it’s worn out.

If you live in a level area, it may be difficult for you to notice your clutch slip. It’s important that if you notice any signs of slipping, you test the vehicle up a hill. If your car is barely moving as it accelerates or you find the revs rising while your car doesn’t match them, then it’s likely slipping.

A low clutch biting point

In the case of a low clutch biting point, as we’ve mentioned, its typically a clutch adjustment problem and the solution may be a simple re-adjustment. Hydraulically actuated clutch systems are generally believed not to be adjustable with a few exceptions that allow you to make some adjustments.

Can I adjust a hydraulic clutch?

Hydraulic clutch systems aren’t designed to be adjustable in the same way you would adjust a mechanical cable clutch.

While there’s a popular belief that all hydraulic actuated clutch systems are non-adjustable or self-adjusting, there are some designs that let you make adjustments to compensate for the typical wear and tear of your clutch disc’s friction material.

What Self-adjusting means

But first, before we continue, we need to be clear on what a self-adjusting clutch refers to. Normally, you want about an inch of free play in your clutch pedal, i.e., the distance your pedal covers where you don’t feel any resistance or rather, the distance your clutch pedal moves before anything happens.

If you feel that, then you’ve got yourself a properly adjusted clutch pedal and it won’t be riding itself. However, over time, as your clutch pedal slowly loses adjustment, the point of engagement also rises higher and higher because of the wear and tear of the friction padding on the clutch disc.

Sooner or later, the clutch pedal’s free play is lost, and your clutch starts riding itself, and the worst part is you may not realize it if you’re not too keen. A hydraulically operated clutch system is designed to automatically make adjustments to compensate for the normal wear and tear.

In some older vehicles, you regularly had to make clutch adjustments, but in the end, customers grew tired of regularly making adjustments and replacing worn-out clutches. In some of these cars, you only had room to make slight alterations in the length of your slave cylinder’s pushrod.

However, these changes were limited and were not meant to compensate for the normal deterioration of your hydraulic clutch due to aging. To satisfy their customers, manufacturers began implementing self-adjusting cable and hydraulic clutch systems which automatically adjust your pedal’s free play over time.

Optimum free play

For your clutch to work correctly, there’s an optimum amount of free play that is needed in the linkage between the clutch lever and pedal. On the one hand, if you have too much free play, the clutch may start dragging, which is quite problematic, especially in heavy traffic.

A clutch drag refers to the tendency of your vehicle to creep forward while in gear when the clutch is depressed fully because of too much clutch linkage clearance.

Conversely, if there’s isn’t enough free play then you might have yourself a slipping clutch. Like we’ve stated, as the friction material on the clutch disc wears down over time, it will require to be adjusted.

It’s recommended to regularly check and adjust your clutch pedal’s free play after every 6,000 miles or as the manufacturer’s handbook specifies. While older vehicle vehicles require you to make adjustments after a certain interval of time, newer ones typically come with a self-adjusting hydraulic clutch system.

When there’s no more room for adjustments

Now, at some point, there’s no more room for making adjustments, in which case, it’s time to get a replacement. And because of normal clutch wear, it will eventually lose its free play.

Unfortunately, unlike the mechanical linkage clutch system where the driver can easily feel the loss of free play that would tell them it’s time to hit the garage, you’ll not be able to detect it in your hydraulic actuated clutch system.

Failing to detect the loss of free pedal play early enough could prematurely wear down your clutch or even cause it to fail. So it’s important that you are spot on about your periodic service checks and always remember to check your clutch for wear regularly, which is something most people forget to do.

The Clutch Problem

What usually happens is having too much clutch pedal free play which is typically caused by burnt-out or loose linkages which can be easily fixed by either replacing or tightening the fitting.

You typically get replacements when it’s completely burnt-out, i.e., it doesn’t have any more room for adjustment, and the point of engagement has become too high. On the other hand, if the engagement point is too low, then there are two possible reasons for it.

It could be that there’s a leak in your master or slave cylinders allowing air and other contaminants to seep through to the hydraulic system; a classic clutch bleeding symptom. If the pedal play improves after bleeding the clutch, then there’s a leak that needs to be found and fixed.

The other reason is that your floor mats are very thick making it impossible for you to depress the clutch pedal all the way down. You’d be surprised how much car travel you can lose with some of these thick floor mats.

Can I adjust a hydraulic clutch?

Most car and garage owners assume that hydraulically actuated clutch systems are generally non-adjustable and don’t refer to the manufacturer’s manual. Fortunately, some hydraulically operated clutch systems allow adjustments to be made on the free play and height of the pedal.

That being said, any adjustments made should follow what the vehicles’ manufacturer’s handbook specifies for a properly adjusted and working clutch. We can’t stress this enough because of the variety of problems that arise with an improperly adjusted clutch.

Anything less or more than the optimum free play will cause a clutch slip since the pressure plate will not be able to exert the required pressure on the clutch disc or place the fork in contact with the clutch which may cause some serious damage.

Moreover, the heat generated from clutch slipping could damage the clutch, it’s release mechanism as well as the flywheel if it gets hot enough, and they may need to be replaced.

If you have an adjustable hydraulic clutch, then your slave cylinder’s pushrod should be fitted with a locknut and threaded. For those of you who are uncomfortable with the engagement point of your clutch, there are plenty of guides on how to adjust a hydraulic clutch.

The symptoms of air in the clutch line

A bad or failing hydraulic clutch will typically produce a few symptoms that alert the keen driver of a potential issue and its time for you to hit the garage. Hydraulic clutches are generally favored for their small form factor and are much easier to install compared to mechanical linkage clutches.

However, as great as they are, they’re not perfect. Hydraulic linkage clutches are particularly susceptible to developing leaks, wearing down and worn seals allow air in which subsequently affects their ability to maintain the required pressure and displace the hydraulic fluid.

These issues often lead to problems with shifting gears and give your clutch pedal an abnormal feel. Stick around as well looks at these and other air in clutch line symptoms, but first, a quick refresher on the basics of the clutch.

So what happens when you have air in your clutch line

If you’ve recently replaced your clutch’s master or slave cylinders, flexible hose or bled it to replenish the fluid, then you need to be careful not to allow air to be sucked in or it may not function properly.

Like we’ve explained above, whenever you depress the clutch pedal, the master cylinder’s pushrod displaces the brake fluid via its flexible hose to the slave cylinder which consequently disengages the clutch.

Compressible Air bubbles

The entire mechanism relies on the ability of your clutch to maintain the hydraulic pressure until it disengages the clutch. Air in the clutch line contaminates your clutch system by forming compressing air bubbles.

The air bubbles dull out the hydraulic pressure transmitted from the master cylinder to the slave cylinder by absorbing some of the generated hydraulic pressure. Consequently, it affects the ability of your hydraulic linkage clutch to disengage the clutch, if it does at all.

By absorbing some of the hydraulic pressure, the air bubbles limit the reach of the slave cylinder’s pushrod which is responsible for moving the clutch fork which engages the diaphragm spring to disengage the clutch disk from the engine’s flywheel.

What causes air to get in the clutch line?

Air usually invades into your hydraulically actuated clutch system via worn-out seals in the clutch’s master or slave cylinders.

The other way air invades your hydraulic system is if you’ve recently replaced your clutch’s master or slave cylinders, bled it or replaced the flexible clutch hose. In which case, it’s a probably human error that allowed air to be sucked into the hydraulic linkage system.

Now that you’ve got the basics on what causes air to sip into the clutch line, here are few symptoms that will help you find out.

Signs of air in the clutch line

The main clutch components affected by air are the pedal and the shifting gears. You might find that you have to turn off your vehicle to be able to change into gear.

  • Clutch pedal sticks to the floor

If you’ve air in the clutch line, the clutch pedal typically tends to stick to the floor of your car. You’ll typically have problems disengaging the clutch and may have to constantly pump it for it to work.

In such a scenario, you’ll find that the problem is usually hydraulic fluid as opposed to a mechanical issue, i.e. an issue with the clutch disc, master or slave cylinders, etc. Its usually accompanied by a spongy or soft feeling clutch pedal, especially between cycles of actuation.

  • Intermittent clutch action

You may also experience intermittent clutch action; where it sometimes shifts as usual while other times, it wants to creep forward. In such a scenario, the hydraulic clutch fails to fully disengage or engage the clutch disc to the engine’s flywheel.

Having an intermittent clutch release is a sign that the problem isn’t with the mechanical components of your hydraulic actuated clutch, rather the hydraulic system. The usual suspect is air and the air bubbles they create that dull the hydraulic pressure transmitted in the system.

Like we’ve stated, the air can invade the hydraulic system by using the burnout seals in your clutch’s slave or master cylinders. A hydraulic actuated clutch master cylinder comes fitted with both external and internal seals that act as one-way seals to seal in the brake fluid. Like every other part of your car, these seals wear out over time and may cause your clutch to start leaking fluid as well as let air slip in the clutch line.

That being said, hydraulically actuated clutch systems, like brake systems don’t suddenly or partially start to allow air in. If you’ve tried bleeding the master cylinder or rest of the system but still can’t get it to work properly, it may point to a different underlying issue.

Be sure to check for leaks as well since they also cause your clutch to sink to the floor as well. However, keep an eye out for other symptoms of air in the clutch line such as having gears shifting a bit hard, a loose clutch pedal, grinding gears and even smell for not fully disengaging.

Signs of a bad clutch slave cylinder

Since your manual transmission vehicle uses a hydraulic clutch system, it’s prone to a variety of issues the main one being leakages. What’s more, as your vehicle accumulates mileage, it also approaches the end of its expected life service.

Wear and tear cause clutch fluid to leak and subsequently affects the ability of your clutch slave cylinder to maintain the required pressure to disengage the clutch. Ignore it, and you’ll have a hard time changing gears and will be dealing with a less responsive clutch pedal.

A bad or failing clutch can not only make your vehicle’s overall drivability unsafe, but it can also make it more difficult and in the process, damage other parts of your transmission. Without further ado, here are the symptoms of a bad or failing clutch slave cylinder.

  • Mushy clutch pedal feel

A typical symptom of a problematic clutch slave cylinder is soft feeling clutch and is also the easiest problem to identify, especially while you’re driving. You’ll notice you’re not getting as much clutch pedal resistance as you normally would and could be caused by a leak in the clutch’s slave cylinder.

  • Weird Engine Noises

If you hear weird car noises, especially when you’ve engaged the gear and are about to release the pedal, then this could be a sign of a failing or bad slave cylinder. It’s normally caused by a leak of the clutch fluid which makes it difficult for it to maintain contact and effectively disengage the clutch.

  • Leaks on engine bay or the floor

Another symptom of bad or failing clutch slave cylinder is finding leaks in the engine bay area or the floor. If your clutch slave cylinder leaks, it will drip the clutch fluid and leave visible traces on the engine bay or the floor

Depending on the extensity of the damage, the leakage on the clutch slave cylinder could affect the overall feel and resistance of your clutch pedal.

  • Loose Pedal

Another easily discernible symptom of failing or bad clutch slave cylinder is if the clutch pedal goes all the way to the floor when depressed. It often happens when one of the valve seals in the clutch slave cylinder is damaged or loss, allowing air to seep into the hydraulic fluid and subsequently contaminating it.

  • Low clutch fluid

Lastly, your clutch fluid levels can also be a good indicator of a failing clutch slave cylinder. With a leaking slave cylinder, you’ll find yourself needing more frequent brake fluid refills since its quickly being depleted.

If that sounds familiar, then be sure to thoroughly check your clutch slave cylinder for holes or cracks that may be causing the leak.

If you notice either of these symptoms, it’s important you take action immediately. The signs of a failing or bad slave cylinder are not to be ignored since they not only compromise your driving safety but can also compromise your clutch system.

What does a low clutch biting point mean?

The infamous biting point, aka friction point, is a clutch control technique designed to give you more control over your vehicle and is typically used in a hill start among other scenarios. It’s probably also the first thing your driving instructor taught you, as well as how to “find” it.

Your clutch’s bite point is the point at which the clutch disc engages your engine’s flywheel. It’s typically half-way through your clutch’s pedal travel; the sweet spot between a fully depressed and released clutch pedal.

That being said, it’s not a given for every vehicle and does vary from manufacturer to manufacturer. While the experienced driver may occasionally use the biting point in a hill start or slow traffic, the learner may find it useful to since it’s a great way of reducing stalling.

There are two basic common problems with your clutch’s biting point; a high and low biting point. With a high biting point; the biting point is much closer to the end point of a fully released clutch pedal and is a good indicator of a worn-out clutch that needs replacing.

Conversely, a low biting point means that the biting point is a lot closer to the end of a fully depressed clutch pedal and is a great indicator of an adjustment problem.

Regularly using the clutch’s biting point will unnecessarily increase its wear and shorten the expected life of your clutch. While it’s important to know and understand it, a more reliable and long term solution is to be more proficient and confident with your driving.

Conclusion

A bad or failing hydraulic clutch will typically produce a few symptoms that alert the keen driver of a potential issue and its time for you to hit the garage. Hydraulic clutches are generally favored for their small form factor and are much easier to install compared to mechanical linkage clutches. However, as great as they are, they’re not perfect. Hydraulic linkage clutches are particularly susceptible to developing leaks, wearing down and worn seals allow air in which subsequently affects their ability to maintain the required pressure and displace the hydraulic fluid.

FAQ

What does it mean when one says the clutch is high?

The phrase is normally used to describe a worn out clutch that is in need of replacement. For most cars, changing the clutch is a labor intensive exercise that will take the mechanic a couple of hours depending on the car. You will notice a certain loss of power if you are driving a car with a high clutch.

How do I know that my clutch is about to fail?

One of the first things you will notice with a faulty clutch system is when you press engage a new gear then press the gas pedal the engine will begin racing but the car is not picking up speed. Sometimes this will be accompanied by an acrid burnt clutch smell or smoke.