Clutch slipping symptoms and diagnosis

Clutch Slipping Symptoms, Diagnosis & Solutions

If your car has clutch slipping problems, it can quickly progress into something that stops your car from getting you from A to B.

Because of this, it’s wise to correctly diagnose and solve those clutch slipping symptoms as quickly as possible to prevent it from turning your car into a driveway ornament.

In this article, I am going to cover the basics of how a clutch works, explain why it can slip, how to be sure clutch slipping is in fact your issue, and the best ways to move forward with a solution.

So let’s get started talking about clutches.

What is a Clutch?

First of all, let’s get on the same page with what a clutch actually is in the context of a car or motorcycle.

If your vehicle has a manual gearbox, it will almost certainly be equipped with a 3rd pedal by the drivers feet. This leftmost pedal is to actuate your clutch.

Car's clutch pedal in footwell

You will actuate your clutch for a couple of reasons, the main one will be to change gears without grinding them. The second reason is to control your car or bike’s movement at slow speed when setting off from a stop, which is especially useful when trying to do a hill start going up hill.

Most clutches in cars and motorcycles, especially modern ones are hydraulically operated. This means that when you press the pedal (or squeeze the clutch lever), you are applying pressure to the hydraulic fluid which pushes down the line and operates the clutch. Brakes work in just the same way between the pedal and the calipers.

On an older vehicle, clutches were mostly cable operated and required adjustment, and a strong leg to operate on more powerful vehicles.

The clutch itself effectively allows you to modulate the drive connection between the engine and the gearbox (or transmission). So with the clutch disengaged (foot pressed on pedal), your engine can run and be revved without drive being transferred to the wheels, or with reduced drive being transferred.

On most cars, the clutch itself is situated directly between the engine and gearbox in a bellhousing that protects it, but is not completely sealed.

How a clutch works

This takes us nicely onto the question of how a clutch works. These systems are seemingly complex to look at, but the secret is that they are actually fundamentally very simple.

Generally clutches are a 4-part system consisting of the below, in order:

  1. Flywheel
  2. Clutch Disc
  3. Pressure Plate
  4. Diaphragm Spring

The Flywheel is a substantial metal disc attached to the engines crankshaft solidly so when the engine runs, the flywheel spins at the engines RPM.

These are often heavy items to dampen the vibration and harshness from the internal combustion engine. It has a contact surface on the outside similar to a smooth brake disc.

The Clutch disc is a floating disc of high friction material, similar to that found in brake pads. This is a wear item and the one generally consumed fastest.

The Pressure Plate sits on the opposite side of the clutch disc to the flywheel and again has a contact surface similar to a brake disc where the clutch disc’s friction material makes contact.

What clamps this system together when the clutch is fully engaged (foot not on the pedal) is a fancy looking contraption called a Diaphragm Spring is actuated.

This is no ordinary coil spring we’re talking about here, it’s shaped very similar to a dinner plate including the beveled edge, although it would be no good as a dinner plate as the metal forms spokes which are not connected at the centre.

Clutch diaphragm spring

Externally, there is a separate central ring (usually a clutch release bearing) which contacts the tips of all of the spokes, this ring is pressed against the diaphragm springs spokes and the result is the solid outside radius of the spring will release its pressure on the back of the pressure plate.

So with no foot on the pedal, the diagraphragm spring has the flywheel, clutch disc and pressure plate all clamped together solid. With a foot on the clutch pedal, the diaphragm spring is pressed in the centre and releases its clamp allowing the flywheel and pressure plate to move independently of each other, or remain still.

What are the Symptoms of a Bad Clutch?

So now we know what a clutch is and how it works, lets cover what the symptoms are of a bad clutch and try to quantify the problem.

Diagnosing a worn clutch can be a little unnerving, and as these things last a very long time, many cars being scrapped with their original clutch still functioning and in place thanks to our throw away culture, it’s not that common for someone to encounter a bad clutch.

Unless you’re a mechanic that is.

If you are well in-tune with your car and have owned it for some time. You begin to build a rapport with how it drives and can become quite astute in noticing subtle changes to the controls such as the clutch pedal feel and where the balancing point is of it.

High Biting Point

If you notice the biting point of your clutch becoming higher and higher, it may be a sign that your clutch is starting to wear out.

Equally, if you’re looking at purchasing a used car, you will want to check where the biting point of the clutch is, if it’s unusually high it can be sign that the clutch isn’t far off due and you can factor this into the price you’d be prepared to pay for the vehicle.

It’s worth bearing in mind however, that all cars and motorcycles have different clutch systems and one manufacturer’s clutch can have a very different biting point to others.

Low Biting Point

When people have clutch problems, the opposite of a high biting point can be the symptom manifesting itself. This symptom is often caused by issues with the hydraulic system or cable that operates the clutch.

If your clutch system has a poorly adjusted cable, or maybe a leaky master cylinder, slave cylinder or clutch line, you can find that you’re needing to press the clutch right down to the floor to apply enough pressure to disengage the clutch.

If your system is hydraulic, this situation can happen quite suddenly if a seal or a line fails, and often you will only have a couple more uses of the clutch pedal before all the fluid escapes and your car is stuck either in or out of gear.

This is a common issue and driving older cars, I have had this problem on two separate occasions, neither of which resulted in an actual issue with the clutch, just the hydraulic system that actuates it. Quite cheap to fix in comparison, although equally inconvenient.

Clutch and flywheel

Clutch Rattles

Another disconcerting symptom of a bad clutch can be rattling. Although in my experience this tends to sound more alarming than the actual problem is.

Again the system which actuates your clutch has another failure point which is the release bearing, also commonly known as a clutch bearing. 

Remember I mentioned the central ring that presses on the diaphragm spring relieving its pressure on the pressure plate? Well this ring is commonly a clutch release bearing, and they can wear out over time.

The rattle in this case will be present as you fire up or switch off a car, the latter being most obvious as you will be removing the noise of the engine which can cover it somewhat.

Another noise symptom of a release bearing is a squeaky chirping sound when the pedal is depressed.

This bearing can be squeaky or rattly for a long time without any further clutch symptom present, although it’s annoying and makes the car sound like a hooptie.

There are of course other potential sources of clutch rattles, such as if your clutch disc’s friction material starts to disintegrate, but this is by far the most common rattle.

How do I know if my clutch is slipping?

If you’re having issues with your clutch and have not noticed high biting point, low biting point or any new rattles, then that doesn’t rule out the clutch as the offending article.

A worn clutch can simply lose its bite between the flywheel and pressure plate causing slip when it’s not wanted such as while driving along, in gear.

This can be a bit harder to spot as you’re cruising along at a constant speed.

If you’re having issues getting in or out of gear, refer back to the previous point about low biting point which can often be the case here.

But if you find your engine revving high when accelerating without the car making progress, that can certainly indicate that some of your engines power is not being transmitted to the wheels and instead is being used to burn up your clutch by spinning it in contact with the flywheel and pressure plate.

If you are driving the car white hard, or trying to set off with gusto out of a junction, this can be pretty dangerous especially if you are pulling out into a gap in traffic as you will find the car making a lot of noise but not a lot of progress forward.

An easy way to know that it’s your clutch spinning up in these scenarios is the very distinctive burned clutch smell which will be strong enough to enter the cabin.

If you drive your car gently but the clutch is slipping slightly while you are cruising along, you may notice this smell when you pull up and get out of the car at your destination.

It’s a difficult smell to describe, but it’s a strong, distinctive smell which is kind of acrid and kind of metallic. You will notice it when you smell it.

What causes clutch slip

Generally this clutch slip will be caused by your flywheel, clutch disc or pressure plate being worn down, or ,maybe a combination of all 3 if your car has done a lot of miles, especially in stop-start traffic.

The clutch is definitely a wear item on a car, especially if it’s a powerful engine and is driven hard. But even economy cars driven gently eventually get worn clutches.

Clutch disc friction material

In the context of a cable clutch, as often found on classic motorcycles. An incorrectly adjusted clutch cable can cause slipping, as it can be adjusted so that the clutch discs never receive the full pressure of the springs to clamp them together fully.

Or at least not clamp them together enough for hard accelerations.

How long will a slipping clutch last?

Generally, if your clutch is slipping because of wear, you could potentially be on borrowed time with your clutch.

For example, if a clutch wears to the point where the clutch disc friction material is worn off completely, you can start getting metal-to-metal contact between the metal the friction material was stuck to and your flywheel and pressure plate.

This can quickly turn a relatively inexpensive clutch disc swap into an expensive full flywheel, clutch disc and pressure plate replacement.

Luckily, these things generally don’t fail catastrophically and all of a sudden, unless you are doing clutch kicks while trying to practise your drifting in a supermarket car park.

If there is a noticeable clutch slipping issue with your car, my advice is to drive is very gently and get it to a reputable mechanic for a replacement at your earliest convenience.

You certainly don’t want to take many journeys in the car while this is a problem through fear of being left stranded having ti pay for recovery.

It’s worth noting that the times you will most wear your clutch are in stop-start traffic situations. So if your mechanic is quite far away but you can cruise there on the open road at a constant speed, that shouldnt be as big of a problem as trying to limp the car through city traffic.

Likewise, if your motorcycle’s cable operated clutch is brand new but the cable is not correctly adjusted, you can find yourself burning up a new clutch far faster than you’d like, maybe in only a few hundred miles if its particularly bad, so it’s well worth correcting this as soon as possible.

How much does it cost to fix a slipping clutch?

There’s really only one way to fix a worn clutch, and that’s to replace it altogether with fresh parts. It is a wear item after all.

Most normal cars, driven by careful owners who have not ridden the clutch (which is driven around with the clutch slightly slipping thanks to their foot being rested on the pedal) should ssee 60,000 or maybe even 80,000 miles out of a clutch.

It’s not even uncommon to see cars with clutches over 100k miles old, especially if they have been used for mainly motorway cruising.

The cost of a clutch replacement can vary massively depending on the type of car or motorcycle we’re talking about.

Generally, it makes sense for your mechanic to replace the pressure plate (usually with integrated diaphragm spring) and clutch disc at the same time, leaving the original flywheel in place.

Due to this, the vast majority of kits available on the market or aftermarket are a kit which includes these pieces. For a typical economy car, you can pick up a clutch kit for around £150-£250. But the sky’s the limit when it comes to performance cars with clutches that can take considerably more torque.

Performance paddle clutch

Flywheels for normal cars can generally cost the same, if not a bit more for a brand new OE part. Luckily this is the item which generally wears the least, so you won’t necessarily ever need to replace it.

As far as labour is concerned, fitting a new clutch is quite an involved job that generally means dropping the car’s gearbox to reach the inside of the bellhousing where the clutch lives.

This means the job can get quite expensive quite quickly and the labour can often be the most expensive item on the bill. You can expect to be charged for half a day’s labour or more for the work which can often be in the £300-£450 range.

This takes the whole bill to around the £550 mark for a normal economy car.

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