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Clutch Symptoms and Their Causes
Posted on: Saturday, December 13, 2008
Clutch Symptoms and Their CausesHere is a quick explanation of likely causes for various clutch problems. Where possible, I mention them in order of their likelihood. In all cases, I am assuming the clutch in the vehicle is the right one, it is correctly installed, and there has been no tampering to deliberately cause a problem. I am addressing only normal use situations.
Slippage:The classic clutch symptom is slippage. Engine revolutions are not fully transferred to the transmission. Power is not fully transmitted to the drive wheels. The engine seems to race but the vehicle does not keep up! Slippage is most often caused by a worn clutch disc. Or, the clutch pressure plate may be weakened by heat, age, or abuse. In either case, it means the vehicle needs a new clutch. Replacing just one clutch part is not good practice. Automotive repair professionals will not attempt such partial repairs. Worn or damaged clutches must be replaced.
Less common causes of slippage include: massive amounts of oil on the clutch (usually causes chatter, not slippage, see below), a broken disc or pressure plate, a release cable binding, or transmission damage. Obviously, an oil-soaked or broken clutch requires replacement. But, even when the problem is external, replacing a slipping clutch may be warranted. Slippage causes almost instant damage to the clutch. Heat produced by the slippage quickly damages friction material, contact surfaces, and springs.
Clutch Release Problems:Clutch release problems are common. Even though the clutch pedal is depressed, you have trouble shifting. In some cases it is impossible to get the transmission into gear. Sometimes there is an accompanying sound of grinding gears! When these symptoms occur, they are most often the result of the clutch not fully disengaging. The transmission input shaft is not allowed to come to a stop. Engine revolutions are still being transmitted to the transmission. Sources for this problem vary according to the type of clutch mechanism your vehicle has.
Mechanical Linkage:Worn pivot points, broken or bent push rod, worn or broken cross-shaft, bent pedal bracket, or cracked firewall can each cause this problem. Usually, several parts are contributing to the problem. This type of mechanism tends to wear and fail with age and continued use.
Cable Operated Clutch:Stretched, frayed or binding cable, broken or bent pedal bracket, or cracked firewall can be the cause. Problems with a cable mechanism will often herald internal clutch problems as well. When something happens inside the clutch that requires extra force to be exerted on the clutch pedal, things break! Cables can also wear simply from age and use.
Hydraulically Operated Clutch:Clutch master cylinder leaking or bypassing pressure, slave cylinder leaking, clutch flex hose leaking, pedal bushings worn or missing, or a cracked firewall can reduce the system's ability to disengage the clutch. Rule of thumb: If the clutch master cylinder is bad, replace both master and slave cylinders as a pair. This will save you future heartache.
Internal clutch Release Problems:Not all release problems are caused by the release mechanism. Things can go wrong inside the clutch as well. A loose damper spring in the clutch disc, bent disc, frozen pilot bearing, collapsed release bearing, or metal shrapnel from a broken cover can cause the clutch to bind and not fully release when the pedal is depressed. The release fork might bend. The pivot ball can wear or break. There are many reasons for a clutch to hang up.
Clutch Chatter:Clutch chatter, a vibration and/or noise when engaging the clutch, is likely to be caused by an internal clutch problem. A warped disc, hotspots on the flywheel or pressure plate surfaces, worn or dry input shaft splines, or worn release bearing.
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