Diagnosing clutch problems is much like diagnosing problems in any other automotive system. The more information you have about the problem, the easier it is to properly diagnose it. Diagnostics should always begin with gathering as much information as possible from the owner of the vehicle by asking questions, such as:
- When is the problem most noticeable?
- How long have you noticed the problem?
- What kind of driving do you normally do?
- Have you had a similar problem in the past? Was it corrected? What repairs were made?
Verify the complaint- After you have gathered the information take the vehicle on a road test. If possible, try to drive with the customer. This will help give a better idea of the owners driving habits. For example, does the driver ride the clutch, downshift at high speeds, or miss shifts? This will give you clues about the source of the problem. Some symptoms of clutch problems are Clutch Slippage, Dragging Clutch, Pulsating Clutch Pedal, Binding Clutch, Noise and Vibrations, Clutch Chatter.
When you are driving the car pay close attention to the action of the clutch during all phases of the operation. Notice where the clutch engages. If the clutch grabs way up on the top of the pedal travel, adjust the freeplay back to specifications. If the clutch slips after adjustment, it needs to be replaced. If the free-play is correct and the car accelerates without slipping, but the clutch slips at higher engine speeds, you can suspect a weak pressure plate. Check the throw out bearing for quiet, smooth operation. Listen for bearing and gear noise while downshifting to make sure that a clutch problem has not caused transmission problems such as a damaged synchronizer.
Clutch Slippage - Clutch slippage is evident when the driver has the clutch engaged and the engine speed increases, but the vehicle’s road speed does not. Slipping is normally most obvious during acceleration and shifting. A road test can determine if the clutch is slipping. Normal acceleration from a stop and several gear positions should provide the conditions needed to witness slipping.
Slippage can also be verified in the shop. Depress the clutch pedal, shift the transmission into high gear, and increase the engine’s speed to around 2200 rpm. Slowly release the pedal until the clutch engages. The engine should stall immediately. If the engine does not stall within a few seconds, the clutch is slipping. If the clutch slips, depress the clutch pedal to end the test quickly.
Dragging Clutch - Clutch dragging occurs when the clutch disc is not fully released when the clutch pedal is fully depressed. This can cause gear clashing, especially when shifting into reverse. The clutch disc, input shaft, and transmission gears should require no more than five (5) seconds to come to a stop after the clutch pedal is depressed. This time is called the “spindown time” and is normal. However, if the time exceeds more than five seconds, clutch drag is evident.
To check for dragging clutch. Start the engine and depress the clutch pedal. Shift the transmission into first gear but do not release the clutch, then shift in neutral. Wait five to ten seconds, then attempt to shift into reverse. If the shift causes gear clash, raise the vehicle and check the clutch linkage. If there are no problems with the linkage, the clutch must be disassembled and inspected. Clutch drag can be caused by a warped disc or pressure plate, a loose disc facing, incorrect clutch pedal adjustment, or a defective release lever.
Pulsating Clutch Pedal - Pedal pulsation is a rapid up-and-down pumping movement of the clutch pedal as the clutch engages and disengages. The movement of the pedal is normally slight but can be felt through the pedal. To test for pulsations, start the engine and slowly depress the clutch pedal. Pay close attention to the pedal as it is being depressed. Very slight pulsations are normal, however if the pulsations are quite noticeable or severe, the clutch assembly needs to be disassembled and inspected. Pedal pulsation is normally caused by broken, bent or warped release levers, a misaligned bell housing, or a warped pressure plate, flywheel, or clutch disc.
Binding Clutch - If the clutch pedal does not operate smoothly, check the clutch linkage or cables for binding. Also check the bearing retainer collar for wear or grooves. Make sure the retainer is lightly lubricated with white lithium grease. If the clutch pedal moves but fails to disengage, check the linkage for wear or improper adjustment. Make sure that the disc is not installed backward. Also check that the disc hub spines are properly lubricated. Examine the release fork to make sure it is on its pivot and that it is not warped, cracked, or excessively worn. Check the condition of the pilot bearing or bushing. A bad pilot bearing can cause the disc to bind by preventing smooth rotation of the input shaft or may allow the input shaft to wobble, causing the disc to be in continual contact with the flywheel or the pressure plate. This problem can cause gear clashing, as well as poor disengagement.
Noise and Vibrations - Noise and vibration problems are best identified by road testing the vehicle. Begin your observations while the transmission is cold. Pay attention to any change in noise as it warms up. Start the engine while the transmission is in neutral. Listen for a change in noise as the clutch pedal is depressed and released. Repeat this cycle with the engine at higher speeds.
Drive the vehicle and shift through all the gears, including reverse. Listen for any change in noise in a particular direction or gear. If the noise is most noticeable in a particular gear, drive the vehicle in that gear and then depress the clutch pedal. Listen for any change in noise. If there is a change, the noise may be amplified by the engine's vibrations. Release the clutch and wait until the original noise returns. Then shift the transmission into neutral, release the clutch, and allow the vehicle to coast. If the noise remains, the cause is undoubtedly in the drive line.
Clutch Chatter - Clutch chatter is shaking or shuddering that is felt when the clutch is engaged. This normally happens when the pressure plate first makes contact with the clutch disc and will stop when the clutch is fully engaged.
To check for chatter, start the engine and completely depress the clutch pedal. Shift the transmission into first gear and increase the engine speed to 1500 rpm. Slowly release the clutch pedal and listen as it begins to engage. If chattering is evident, depress the clutch pedal and reduce engine speed immediately to prevent damage to the clutch parts.
Clutch chatter is normally caused by broken engine mounts and glazed clutch and or flywheel or pressure plate facings. Leaks into the clutch can lead to glazing. Possible sources of leaks are the engine's rear main seal, transmission input shaft seal, and clutch slave cylinder. The engine and transmission mounts should also be checked for looseness, breakage, or wear. Chatter can also result from uneven engagement, which can be caused by a worn front bearing retainer or release fork. Other possible causes for chatter are a bent clutch disc, burned or damaged facing, excessive heat, damaged pressure plate, pressure plate has excessive runout, and worn or damaged pilot bearing.
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