In order to work efficiently, the clutch needs the right amount of play in the linkage between the foot pedal and the clutch operating lever (also known as the release arm or fork). Anything less than the correct amount of free play (or clearance) will result in clutch slip, because the pressure plate will be unable to exert its full pressure on the friction plate.
Failure to cure this fault will quickly lead to a burned-out friction plate, and possibly a ruined pressure plate. If, however, there is too much clearance in the clutch linkage, the car tends to creep forwards when in gear with the clutch pedal fully depressed.
This is known as clutch drag, and it can cause difficulties in heavy traffic.
It is generally better, however to have too much play in the clutch linkage than too little.
The linkage should be checked and, if necessary, adjusted about every 10,000km, or as specified in the maker’s service schedule. Wear on the friction plate and on the linkage will eventually alter the maker’s setting.
Most modern cars have a diaphragm-spring clutch operated either mechanically or hydraulically.
On most cars, mechanical clutch-linkage clearance is measured and adjusted underneath the car. On some the makers advise checking free play a specific measurement between pedal positions – at the pedal, although adjustment may be made underneath
On some cars – many Hondas and Toyotas, for example – checking and adjustment can be done at the bulkhead under the bonnet.
Wherever adjustment is made, the same principles apply to all cable linkages. They are adjusted by either increasing or decreasing the lengths of the inner and outer cables in relation to each other. If there is not enough clearance in the linkage, the inner cable has to be made longer. If there is too much, it has to be made shorter.
Check your car handbook or service manual to find the exact amount of clearance required and how it should be measured.
In an emergency, as long as you ensure that there is play in the linkage, the clutch should perform well enough. Check it and adjust to the correct clearance as soon as possible or take it to a clutch repair center.
On a few old cars, such as the Vauxhall Cavalier, there is a constant-contact release bearing – this is adjusted to give no free play at all in the linkage.
Although some hydraulic clutches can be adjusted, many are self-adjusting. Check in your car handbook or service manual.
If slip occurs on a self-adjusting clutch, the clutch has to be overhauled. If drag occurs, the hydraulics may be at fault (See Checking and removing a clutch master cylinder). Otherwise, renew the clutch.
Full source credit: https://www.howacarworks.com/transmission/adjusting-the-clutch
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