The main purpose of the clutch is to temporarily separate the transmission and engine and then smoothly connect them. These operations are important while driving because they provide control of the manual transmission: starting, braking, stopping and shifting gears. If the adjustment of the free play of the corresponding pedal is violated, driving the vehicle becomes difficult - the car accelerates poorly and slips, there is a crunch when changing gears, and it becomes impossible to move. How to adjust the clutch, and what problems can occur if this pedal is not adjusted correctly?
Clutch structure and mechanism
Today, most vehicles have a single-plate friction type clutch, which has two main components: a drive and a mechanism. The first is located on static parts of the body or frame. To briefly disconnect the engine crankshaft from the gearbox shaft, you need to press the clutch pedal all the way, “disengaging it.” When pressed, the rod directs pressure from the master cylinder piston to the working cylinder. The latter moves the force to the mechanism through the release fork and the pressure bearing. At the moment the pressure decreases, the drive return springs will return the elements to their original positions.
Most often, you can find several types of drives on cars:
- Hydraulic. The design includes a tube with high pressure of the working fluid, which powers all the mechanisms.
- Mechanical. The force with which the pedal is depressed is transmitted by a cable to the release fork.
- Electric. The electric motor drives the cable, which acts similarly to a mechanical drive.
- Pneumatic. Most often used on trucks, in order to reduce the required effort to release the pedal. The design includes a pneumatic booster, which affects the piston valves.
The clutch design in the crankcase consists of several discs: driven and pressure. The first is located on the gearbox shaft splines, and the second is on the flywheel housing. Separately, there are release levers on the ball joints, and the driven disk is pivotally connected to the structure.
The driven disc is statically secured between the crankshaft and the pressure plate when the clutch is completely disengaged. The coupled structure transmits torque from the crankshaft to the gearbox shaft. When the pedal is depressed, the thrust is transferred and the fork moves the clutch. The latter, using levers, moves the pressure plate.
Features of clutch in automatic and manual transmission
The clutch can be single or double disc. Depending on the principle of operation, it is divided into “wet” (in the presence of oil or lubricant) and “dry”. So, automatic transmissions most often have a multi-plate wet clutch.
Due to the absence of a pedal, the force in the automatic transmission is transmitted by a servo drive, or actuator. The entire installation is controlled using a control unit and a hydraulic distributor. In a manual transmission, two types of clutch operate alternately. Actuators differ in their operating principle:
- Electric (otherwise known as a stepper motor). The control unit constantly receives data on engine speed, and at a certain speed the servo drive receives a corresponding signal. The transmission mechanism disconnects the crankshaft and input shaft.
- Hydraulic – hydraulic cylinder. In the drive mechanism, the oil pump transmits pressure to the distributor, under certain conditions to the servo drive. After changing gears, the pump force decreases.
Reasons for adjusting the clutch pedal
It is important to understand that improper clutch operation may create virtually no problems when driving, but nevertheless it will significantly reduce the life of the clutch mechanism and gearbox. Over time, the discs wear out, which increases the clearance between the bearing and discs.
There are two main reasons why pedal adjustment is necessary:
- Replacing the clutch cable in a mechanical drive or replacing the slave cylinder. After such an intervention in the operating structure of the drive structure, adjustment is a mandatory procedure.
- Changing the pedal stroke. Excessive travel can occur as the friction linings wear out. To avoid negative consequences, it is better to regularly measure the working stroke.
In most foreign cars, adjustment is not required, since they have a self-regulating mechanism installed. The difference between the foreign-made design and the domestic one lies in some details of the ratchet mechanism.
A separate reason for adjustment is interruptions in the operation of the gearbox. If the desired gear does not engage, or is difficult to engage, the clutch is not pressed enough. Otherwise, the car may not move when the clutch is engaged. Then we can talk about a highly tensioned mechanical drive cable.
How to check pedal free play
Clutch free play is the period of pedal movement from the moment it is pressed to the moment it is activated. You can notice that when you press the clutch, at first there is no proper resistance, and somewhere in the middle of the stroke an increase in rigidity appears.
If the vehicle starts moving immediately when you touch the pedal, then it is better to make the adjustment urgently, since there is no free play at all. Otherwise, the pedal can be pressed to the floor, but the car does not move.
Free play is required for all manual transmissions, since it indicates clearance between the fork, bearing and disc levers and prevents constant contact of the bearing with other elements of the mechanism. It is important to monitor the size of the free play, because if it is too large, full pressure will not be enough to transmit sufficient force to squeeze the drive disk.
A separate reason for checking free play is noise and jerking when interacting with the clutch. You can measure this indicator yourself using a ruler.
It is necessary to measure the perpendicular distance from the floor to the pressure pad. Next, when you gently press the pedal, you should measure the stroke until resistance first appears. The result must be checked against the data in the vehicle's operating manual.
The general average clutch stroke for a car is 160 mm. It is recommended to carry out preventive maintenance and adjustment every 20 thousand km.
Are adjustments done differently on different brands of cars?
If the car is equipped with a manual transmission, then this setting is identical for all car models. With automatic transmissions, such adjustments are not made because the driver does not engage the clutch.
The only thing that can be adjusted at home without disassembling the basket is setting the optimal amplitude of the pedal. The driving disc should not engage the driven disc either early or late so that the driver can smoothly release the pedal.
The only way the process may differ on a separate car is the position of the adjusting mechanisms. In one car, it is enough to simply lift the hood and the cable approaches the box from above, and in another, remove the air filter module or battery.
Checking the gap and adjusting the clutch fork
To check the operation of the clutch fork, you need to find the threaded bushings at the end of the clutch cable and measure the difference in the gap between them at rest and in the recessed position. The ruler must be placed near the cable and the edge of the housing. After the lever is pressed all the way, the distance is measured.
The second step is to pull out the lever and repeat the measurement. The indicators are compared against the manufacturer's data and, if necessary, adjusted. To do this, loosen the lock nut (VW has a wing nut) and turn it out as necessary, reducing or increasing the gap. After all the actions, firmly fix the clutch pedal and squeeze it several times. To check the effectiveness of the actions taken, the measurements must be repeated and the results compared.
Step-by-step procedure for tensioning the clutch cable on a VAZ-2114
In order to change the length of the clutch cable, we only need a wrench.
1. First of all, open the hood and look for the nuts on the gearbox housing located at the very end of the adjustment unit. Two 17mm bolts.
The clutch cable is marked with a red marker.
2. Next, loosen the locking nut, and then change the position of the adjusting nut, tightening or unscrewing it to the required length.
The nuts will unscrew easily with any pressure.
3. When the nut is screwed on, the clutch pedal will rise, increasing the length of its distance, and if it is unscrewed, the distance to the floor will decrease, pressing the pedal closer to the floor.
The arrow marks the nut for fixing.
There is no doubt that such work is much easier to carry out in the company of an assistant.
4. Upon completion of all adjustment work, the locking nut is tightened as close to the adjusting nut as possible.
When carrying out such procedures, make sure that the clutch cable itself is intact, that there is no damage or scuffing on its body and shell, and that it moves freely inside the elements supporting it. If something like this is discovered, then it is best to replace the cable with a new one, since the wear of the supported one will only increase, and it is impossible to talk about the reliability of the work performed.
Checking work
After you have completed this work, you need to check the correctness of the work performed.
- First, measure the travel of the clutch pedal.
- With the engine turned off, depress the clutch pedal several times and return it to its place.
- Next, we take a new measurement and clarify the received readings.
- If they have not changed compared to the first measurements, then the work has been completed, correctly, and the first stage of verification can be considered completed.
- And if they differ from the first indicators, it means that the locking nut was not tightened tightly, and the adjustment process must be carried out again.
There is one rule among car enthusiasts! A properly adjusted clutch should begin to engage approximately halfway through the pedal stroke.
The following test can definitively indicate the serviceability and correctly adjusted clutch:
- The car must be placed on a flat surface, the handbrake must be turned on, and the engine must be running.
- Next, we turn on the gear and try to start moving.
- If at this moment, when the clutch pedal is not pressed, the car stalls, this means that the adjustment was made correctly.
- And if this does not happen, the car is running in gear with the clutch pedal not pressed, then this will indicate clutch slipping, which will need adjustment.
How to check and adjust a hydraulic clutch
The operation of a mechanical and hydraulic drive has its own design differences. In this regard, in order to adjust the hydraulic clutch, it is necessary to check the total length from the pusher rod to the fork. According to the standards, it should be about 5 mm.
Then disconnect the spring from the working cylinder bracket. There is an adjustment nut on the rod, by unscrewing which you can change the stroke of the fork to the desired result. The general concepts of changing the working and free play may differ depending on the vehicle manufacturer. Before you begin self-adjustment, you need to read the manual for your vehicle or watch training videos:
As you can see, there are no particular difficulties in adjusting and setting the clutch. However, a beginner should carefully follow all instructions and advice from experts. To get the most effective result, it is better to first become familiar with the operating principle of the clutch mechanism.
When the trip actuator needs checking
The free play of the clutch pedal must be checked and adjusted every 20 thousand km. This also needs to be done if the car starts to move at the very beginning or at the end of releasing the pedal. A correctly adjusted clutch release drive causes the car to start moving when the pedal is released approximately halfway.
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Adjustment of the drive with hydraulics and with a cable is slightly different. To adjust the hydraulic drive, as a rule, you need a pit or overpass. Cable adjustment is usually done in the engine compartment from above, simply by opening the hood.
