Why does the clutch slip?
Mechanical, robotized and some variator gearboxes transmit the rotation from the engine to the wheel drives through the clutch. Depending on your driving style and gearbox type, its average service life is 50-150 thousand km. The need for its replacement is indicated by slipping of the disc. But not always the clutch slips only because of wear. The reason may lie in contamination or wrong adjustment. The exact answer to the question “Why, when you hitch, the clutch smells?” can be found in the article.
Signs of a slipping clutch
If the car has a slipping clutch, the signs of this malfunction can be easily noticed.The car starts softer, takes longer to accelerate. Also, when trying to pick up speed rapidly, engine rpm floats, and from under the hood comes an unpleasant smell of burned friction linings.
All hints on how to understand if the clutch is stuck, and the main causes of malfunctioning of this transmission unit are collected in the table below.
|Why the clutch slips: causes of slippage and what to do|
|Indirect symptoms||Causes||How to correct?|
|The clutch is not pressed out completely, there is a smell at long pressing the pedal||Insufficient clutch pedal travel, improper actuator adjustment||Adjust the clutch pedal and actuator, check release bearing|
|Clutch sticks when the pedal is fully released||Dirt and oil on friction discs. Usually appears after repair, careless oil replacement, and also if the cylinder-head gasket, crankshaft oil seal or gearbox primary shaft is leaking.||Wash the disc, flywheel and clutch cover with petrol or other solvent and let dry.|
|Clutch is not depressed or pressed too easily, transmissions are shifted with jerks, crunch and only when synchronizers are actuated||Failure of hydraulic or mechanical drive of the clutch release mechanism||Replace defective parts of actuators and adjust them|
|Failure of diaphragm spring of the release mechanism||Replace the clutch basket with a new one|
|RPMs are fluctuating, it takes very long to accelerate or does not move at all in any gear||Critical friction layer is worn out.||Replace friction plate|
|Clutch slips suddenly, especially when trying to accelerate suddenly, the vehicle vibrates||Deformation of flywheel, uneven wear of friction surface||If flywheel is slightly worn, you should rebalance it, if it is significantly worn or deformed replace it for a new one.|
|Unusual sounds (crunch, howling, knock) when the pedal is depressed, problems with gear engagement, too tight or soft pedal stroke||Wear in release bearing||Replace defective bearing with new one, adjust actuator mechanisms|
When the clutch slows down, the reasons for such behavior may be different, but the result in most cases comes down to the replacement of parts. As the disassembly of the gearbox for access to the clutch is a time-consuming operation, it is recommended to change the parts as a complete set (the basket, drive plate, release bearing, and sometimes the flywheel).
Causes of clutch slipping
The answer to the question “why is the clutch stuck on the car?” lies in the peculiarities of the design of this mechanism. It consists of several adjacent to each other discs, transmitting torque from the engine to the gearbox. Normally, there is a large friction force between them, which is removed when the pedal is pressed. When these discs are worn, dirty or the adjustment of the pressure is knocked down – the friction becomes insufficient even with the released pedal, and there is a slippage of the clutch discs in relation to each other.
Overheating is a common cause of clutch slipping
The reasons why the clutch slips, not always lie in its wear. Sometimes slipping occurs due to contamination of the surface of the discs, reducing the friction force, as well as a violation of the clutch drive settings. The answer to the question “why does the clutch stink when you hitch?” is often overheating. If to try to drive out of mud or snow on the stuck car, repeatedly touching up and changing gears, discs are exposed to increased load, overheat and the friction force decreases. Therefore, if the clutch became slipping – the reason is either in its malfunction, or in extreme operating conditions.
Why is the new clutch slipping? The most probable reason is the wrong assembly or adjustment of knot (for example, the installed by the wrong side of the slave disk)
What are the possible consequences of a slipping clutch disc.
Regardless of the cause of malfunction, the consequences of slipping clutch does not promise anything good and are fraught with the following problems:
- increased fuel consumption;
- Overheating of the gearbox (especially in the case of a robot);
- Accelerated wear and tear of gearbox oil;
- Wear of the transmission’s primary shaft and bearings;
- irregular surface wear and deformation of flywheel;
- Complete failure of the clutch.
When the friction plates wear down to the rivets, at a certain moment they are ripped off the disc. Because of it not only ability to move is lost (connection of the engine with a gearbox completely disappears), and a box bell is polluted by reinforcing fiberglass from the crumbled overlays. Its cleaning is an unpleasant and troublesome procedure.
Why the clutch slows down only under certain conditions
There are various reasons for clutch slipping at high revolutions, at speed or after car standstill. The most common ones are:
Characteristic signs of clutch wear
- Improper installation or adjustment;
- ambient temperature;
- Aggressive driving;
- Heavy load (e.g. trailer);
- natural wear of parts.
If the slipping of the disc occurs only in certain conditions, for example, in the cold, the clutch slips in 3rd and 4th gear, or if you changed the clutch, and it slips, you should consider the options that will be discussed below to identify the specific fault. All the main symptoms and causes of transmission slipping are presented in the table.
|Problem||Cause||What to do|
|the clutch is slipping in cold or winter||Cold clutch disk is already hot. when heated, the body has the property to expand, so the heated disk begins to press against the also warmed up basket and flywheel.||If the clutch is stuck in the cold, you can drive it, but do not postpone the repair, as this is usually a sign of a large depletion of the friction surfaces.|
|water (snow) got into the bell jar.||if the clutch sticks in the cold because of water – you just need to let it warm up and dry.|
|the clutch sticks when the clutch is hot||the friction force decreases when heated, so the hot clutch stalls and can’t transmit high torque from the engine to the gearbox||In the case of “wet” clutch with an oil bath (usually used in “robots” dsg and the like) you should check the lubrication amount first, maybe it’s just the lack of oil.|
|the clutch is stuck after overcoming a ford or large puddles||If after overcoming a ford, driving through mud and puddles or in heavy rain the clutch slows down – the friction discs became wet/dirty.||Do not squeeze the clutch in water or mud to avoid contamination.|
|the clutch is stuck after repairs||parts are worn out.||Check the clutch adjustment and run in the clutch.|
|Incorrect drive adjustment||Check clutch actuator and adjust the clutch release mechanism.|
|Improper assembly||Check the clutch for proper assembly, check the manual, assemble correctly.|
|parts are not compatible or old parts are worn||If the clutch slips after changing some of its parts (for example, the disk is new and the basket is old) check if the parts fit to each other and if the old parts have excessive wear.|
|the clutch is slipping.||improper adjustment (crankcase is overextended)||check adjustment, retighten the pressure on the basket.|
|Improper assembly||check to see if the assembly is correct, reassemble correctly|
|Selected parts not compatible||Compare the new and the old parts and their part numbers, if found|
If there is slippage in the clutch caused by incorrect clutch adjustment or a lack of oil (for wet type systems), it is important to correct this fault as soon as possible. Otherwise, the discs will overheat all the time, wear out quickly and the repair will be much more expensive!
How do I check if the clutch is slipping?
There are three methods to check if the clutch is slipping on a manual transmission. Its work is well controlled by the driver. But there are no effective methods on the robot or variator. Their automation is able to partially mask the symptoms of the problem, so the actual techniques for mechanics do not always work. On how to determine that the clutch is stuck on different types of boxes, detailed below.
Stuck clutch on mechanics: how to determine?
The main reason for the wear friction linings clutch slipping, is the reduction of pressure force between the disks due to decreasing their thickness. There are 3 main ways to check if an automatic transmission clutch is slipping:
- Starting in a high gear. To check if the clutch is stuck on a mechanic, you need to put it in 4th or 5th gear and try to start. If the engine stalls – everything is normal. If even at rather low (up to 3000 rpm) rpm a car starts moving – slipping of a disk is evident.
- Test with the handbrake. For this test you need to block the wheels of the car with parking brake and try to start in first gear. If the engine stalls or (on front-wheel drive) the wheel slips, everything is OK. If the wheels are stationary, but the engine continues to run in gear – then the clutch began to slip.
- Sharp acceleration test . For this test, you need to switch to a higher (4, 5, 6) gear in motion and sharply accelerate. If the car picks up speed synchronously with the increase of revolutions on the tachometer, there is no problem. If revolutions are floating, they increase sharply without acceleration (variator effect) – the clutch or disk is obviously slipping.
Before checking whether the new clutch is stuck or not, you should verify the correctness of assembly and adjustment of the assembly. Sometimes, if the reason is only in insufficient adjustment of new parts to each other, the slipping symptoms go away after several hundreds of kilometers.
How to diagnose whether the clutch is slipping on the robot?
To understand whether clutch “robot” slipping or not, you can put the box in manual mode, put it in top gear and give gas to the floor, but it does not always help. The same goes for starting with the handbrake.
The most effective way to determine clutch wear on a robot box is to connect with an OBD-2 scanner to the ECU and read the errors with a diagnostic app. Transmission related malfunctions are indicated by codes from P07xx to P09xx, and excessive clutch slippage is indicated by error P0811
Explanation of error P0811
Modern transmissions such as VAG’s DSG, Mercedes’ Speedshift, BMW’s DCT and other similar designs have a double clutch. The latest generations use a self-winding wet clutch, which does not need adjustment because it automatically adjusts the gap as it is worn out. Older and simpler “robots” (like the VAZ 2182 transmission) have the usual dry single-plate clutch.
It is most difficult to determine that a self-lifting clutch is slipping, since the automatics smooth out the manifestations. Excessive clearance is eliminated by the self-clutch mechanism. Therefore, problems with adjustment can be excluded in such case. But if a clutch of DSG 7 or similar automatic transmission slams, it is necessary to check oil in it at once, and only then to be engaged in tests.
Stuck clutch on automatic transmission: what to do?
Conventional torque converter automatic transmissions have a torque converter (“bablik”), that is why there is no question what to do if the clutch sticks, in this case. If it seems to you that clutch slips on automatic, the cause is usually in failure of other units:
- Friction clutches of the automatic transmission slip . Friction clutches are a mini version of a wet multi-disc clutch, separate for each gear. Exactly at their wear it seems that clutch on automatic transmission has started to slip, in fact, symptoms are similar: revolutions are floating, car sluggishly accelerates, there are jerks in motion.
- It is the torque converter that is failing. Worn “bagel”, acting as the main clutch, can also slip. If the car sluggishly picks up speed, the engine constantly starts holding higher revs (although the load has not increased), fuel consumption has increased – the torque converter is worn.
If you have symptoms of clutch slipping on automatic, it is necessary to diagnose a box. Errors (codes from P07xx to P09xx), read via OBD-2 will help to indicate the general cause, but the concrete degree of failure will be revealed only by fault finding at service station.
Stuck clutch on the variator: how to determine and what to do?
If the clutch on the variator is stuck, it is difficult to identify the defect and the cause without diagnosis. It’s necessary to read the errors and, if the corresponding codes are present, go to the service for detailed defectoscopy and repair. Such peculiarity is connected with the principle of work of variator boxes.
Diagnosing the CVTz50 program
Continuously variable transmissions can be equipped with either a clutch or a torque converter. Multitronic transmissions on Audi and Multimatic on Hondas are equipped with a wet clutch, Hyper on Nissan has an electromagnetic clutch, and ZF Transamtic variators are equipped with an automatic centrifugal clutch. These mechanisms are capable of slipping, just like the mechanics, but the variator masks the symptoms as much as possible.
Can it be driven if the clutch slips?
It is difficult to unequivocally answer the question “If the clutch slips, is it possible to drive?” If the problem is not strongly pronounced, and there is no possibility to eliminate it quickly, you can, but observe a number of precautions:
- avoid sudden starts and accelerations;
- Less engine braking;
- Do not sharply release the clutch pedal when shifting gears;
- do not overload the vehicle;
- Do not tow trailers and cars.
If you have got the clutch stuck – don’t try to overtake other cars, especially if the road is narrow (one lane in both directions) or you need to get ahead of several cars. It is dangerous, because if the clutch is stuck strongly when you try to accelerate, you may not have time to safely perform a maneuver when the oncoming car!
In general, riding on a worn clutch is undesirable, so do not procrastinate long with the repair. The sooner the problem is eliminated, the smaller will be the scale of consequences and the cheaper will be the repair.
Car mechanic with 20 years of experience in the repair and maintenance of cars of different brands. Main area: diagnostics and mechanics.
Why is the clutch stuck in the car and how to fix it?
Traditionally, the main components of the car are considered to be its engine and transmission. The first converts thermal energy into kinetic energy, the second transmits torque to the wheels. But without a clutch, both units are useless – it is the clutch that provides the connection between the engine and the transmission.
Like the powertrain, the clutch is subject to high loads, which do not always go unnoticed. The main malfunction of the clutch is considered to be its slippage.
This term refers to the inability to provide lossless torque transfer to the transmission. It, in its turn, is fraught with loss of car dynamics, occurrence of vibrations and extraneous sounds while shifting gears.
Why the clutch slows down
Let’s briefly describe the principle of clutch operation. When you press the pedal there is a transfer of momentum to the fork and through it – to the release bearing. It in turn presses on the petals of the spring, moving apart the pressure plate and the slave disk. The latter disengages from flywheel, and the box intake shaft remains without torque.
When they say that the car clutch drives, it means that it does not engage fully. That is, pressing the pedal does not result in the complete disengagement of the box shaft from the motor flywheel.
Let’s consider the main reasons for this condition:
- The actuator is not adjusted. This means that even full, up to the stop, pressing the pedal is not enough to completely disengage the crankshaft from the friction lining. Usually this kind of trouble appears after the repair work has been done;
- Deformation of the slave plate. This change in geometry causes the friction lining to remain in contact with the flywheel after disengagement of the pressure plate in the deformed area. If there is severe end play, the deformed disc should be replaced. A symptom of this condition is that the car vibrates when starting off;
- Loosening of the diaphragm spring reeds. The consequences are the same as for insufficient pedal stroke – the pressure plate doesn’t fully disengage from the idler plate. The paddles can break, with the same consequences. This usually happens because of a factory defect, or because the actuator is not properly adjusted. The main reason the paddles come loose is natural: metal fatigue;
- the clutch can slip due to a faulty hydraulic system. It can be depressurization of the system, when the leakage of brake fluid provoked the pressure drop in the system and inability to disengage the clutch completely. It is not excluded also the breakdown of the operating cylinder, due to which the crankshaft remains in partial engagement with the primary shaft of the box;
- loss of mobility of the cable drive. The metal cable becomes loose over time, increasing in cross-section in some areas. This leads to its jamming, although it seems to the driver that the pedal is fully depressed. In this case the clutch will also slip;
- The slave disk can also lose mobility. It happens because of grease drying out, dust and dirt getting on the working surface, as well as because of uneven wear of splines. In such cases, when the pedal is depressed, the clearance between the pressure plate and the flywheel required for their separation is not achieved;
- Another reason for the clutch being driven may be a deformation of the flywheel. When it becomes radially warped or has significant galling, the flywheel will not fully disengage from the friction either. Since the flywheel is a massive part, if it’s bent, you’ll usually get vibration, especially when starting off;
- the bending of the fork, which is responsible for the release bearing movement, is also possible. In this case, the stroke is appropriately reduced, with the corresponding consequences.
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Signs of a malfunctioning clutch
Problems in the functioning of the clutch always affect the behavior of the car. But drivers, especially inexperienced drivers, do not always associate the appeared changes in the movement of the car with the work of the clutch. Let’s consider how to independently check whether the clutch is slipping.
The most common symptom indicating the occurrence of malfunctions in this unit is incomplete disengagement. This malfunction can manifest itself in different ways. In some cases, the car may move jerkily, there may be a vibration when depressing the pedal, not excluded the appearance of extraneous noises when shifting gears.
In most cases, if the clutch is not fully disengaged, when the engine is running there are problems with shifting gears of the box, and you can hear a grinding, cracking and other abnormal sounds. With some faults you may notice an increase in the free travel of the pedal.
Often slipping of the clutch is accompanied by a burning smell – it is burned plates of the slave disc. Indirect sign of clutch problems – increase of fuel consumption, increased engine heating, noticeable deterioration of dynamics.
But since similar symptoms are also characteristic of some other malfunctions, it is desirable to perform a thorough diagnosis of the car when they occur.
Slippage is often a consequence of improper use of the vehicle. There is a category of drivers who like to start with slippage – in such cases, the clutch does not go for a long time. Driving off-road leads to the same results, when the car gets stuck in mud or snow, and to get out, the driver begins to accelerate with the half-pressed clutch pedal.
If the release bearing is broken, a shrill squeal is heard when the pedal is depressed, indicating the need for replacement.
If there are several signs of clutch slipping, you can check the assembly yourself, without resorting to paid specialists. A rough algorithm of actions:
- Start the engine, pre-tightening the parking brake to the stop;
- Engage first gear and try to move slowly with the handbrake stuck;
- press the accelerator pedal and release the clutch at the same time;
- if the engine stalls, it will indicate that there is no problem – with the handbrake tightened this is how it should be;
- if engine continues to work – incomplete separation of shafts of a box and a power unit is obvious.
What to do if the clutch is stuck
When the symptoms of malfunction are obvious, it does not mean that it is necessary to perform expensive repairs, consisting in the complete replacement of the node for a new one. In a number of cases, it is worth trying to solve the problems yourself. The main thing is to determine what is the cause of clutch slipping.
If there is wear of friction clutches, your actions will depend on the degree of their wear. Measure the distance between the rivets and the working surface. If it is less than 0.2 mm, you can try to adjust the pedal free play. If the gap is larger, you can’t do without replacing the idler disc, which is made complete with pads.
If during visual inspection you can find traces of oil on frictions – this can indicate a clogged flywheel drainage duct or the presence of grease in the gearbox above the allowable amount. Once the cause is identified and corrected, the pads can be cleaned and then thoroughly dried. Washing should be done with kerosene and drying with a lint-free rag. It is advisable to sand the pads with sandpaper afterwards.
Swollen rubber seals and other hydraulic drive parts are another common reason why the car clutch slows down. The way to fix it is as follows:
- Remove the master and slave cylinders;
- Thoroughly flush the system with any alcoholic fluid;
- Replace all the rubber parts, which have significantly lost their original shape, with new ones;
- we clean the compensating holes from contamination;
- replace the brake fluid and pump the brakes.
If the pressure plates have lost their elasticity, their ability to exert pressure on the pressure plate will weaken, and then the clutch will not fully disengage. This problem is common in older cars (10 years and older). To check the fact of the weakening of the springs, it is necessary to remove the clutch disc. If the fact is confirmed, replace the springs with new ones.