How many times have you been to the doctor or hospital for some ailment and the diagnosis was wrong? Getting to the root of most any problem within a complex situation is tough-even for professionals. And while you may take a trip to the emergency room for a pesky or persistent headache that could be some sort of allergy or worse, the symptoms can be all too similar for a number of scenarios.
Mechanical problems are quite comparable. If your truck doesn't start, it could be something as simple as an empty gas tank, clogged fuel filter, bad coil, or a multitude of other possibilities, but in order to diagnose the cause, we must rule out what we know it's not.
Last month we covered the basics on clutches as far as the most popular for street use, how they work, and the parts that are used in conjunction, like pressure plates, flywheels, and throwout bearings. This month we are looking into common clutch failures and how to diagnose the problem that caused the damage in the first place. If your clutch did more than just wear out and failed prematurely, it's very important to figure out why, instead of just replacing the parts and having them fail again; wasting lots of time and money-especially if you farm the work out!
The assembly and installation of the clutch components has plenty to do with the success and life of the parts; the other main factor is your personal driving style/habits. If you are working on the stock-type clutch for your truck, it's always wise to have a copy of the factory manual for its installation/maintenance specs, like bolt torque specs, pedal freeplay, if any special tools are required, and of course the actual R&R of the parts. While under your truck with the transmission out, be sure and check all related clutch parts for wear or possible problems. The clutch linkage starting from the clutch pedal bushings, to the bell crank (aka Z-bar), to the clutch fork and pivot ball, should be inspected for wear or damage. If you find any questionable parts, they should be repaired or replaced. If your truck has a hydraulic release system, check for any hydraulic leaks in the clutch master and hoses. If your vehicle is cable equipped, the cable should be checked for damage, stretch, fraying, excessive resistance, or binding. If any of these conditions are found, replace the clutch cable and always inspect the throwout bearing collar for signs of wear or galling.
Here's a list of do's and don'ts when it comes time to replace your clutch:
It's simple and obvious, but make sure you have the correct replacement parts before installing any of them, as well as the proper clutch alignment tool. Failure to use a pilot tool to align the clutch disc could result in damage to the disc during installation of the transmission.
Always check the new clutch disc for proper fitment on the transmission input shaft prior to installation. Make sure the input shaft splines are free of wear and twisting.
Whenever you have the clutch out, even if you don't replace it, it's usually a good idea to replace the old throwout bearing and pilot bearing while you're there. They are inexpensive compared to pulling the clutch out again, and I speak from experience! About 10 years ago, I had a '50 Ford I replaced a clutch in. I bought an old but N.O.S. throwout bearing that started squealing no less than three days later, and I had to replace it again.
Never combine a worn pressure plate with a new clutch disc or vice versa. Always replace both the pressure plate and clutch disc with new components.
Replace any worn components such as input shaft collars, clutch forks, slave /master cylinders, etc.
Always properly resurface or replace the flywheel. Resurfacing a flywheel with any device (say an angle grinder) other than a dedicated flywheel-resurfacing machine is not recommended. Also, always clean the surfaces of the pressure plate and flywheel with brake parts cleaner or acetone before installing.
Be sure to install the clutch disc with the side indicating "flywheel side" against the flywheel. If your clutch disc is not marked indicating which side of the clutch disc is the flywheel side, please contact its manufacturer.
Always torque all hardware to factory specifications. Replace hardware if it's worn or if the factory service manual recommends replacement. Proper hardware (shouldered bolts, dowel pins, etc.) used to affix the pressure plate to the flywheel and the flywheel to the crankshaft are special pieces and NOT ordinary hardware. Failure to use proper hardware could result in a vibration, improper clutch operation, or clutch failure.
Do not allow any petroleum-based products (grease, oil, lube, and so on) to contaminate the clutch disc friction material. If contaminated, the disc may cause clutch chatter, slippage, premature wear, or improper clutch operation.
Avoid mixing brands within the clutch system. Most companies design their products to work best with their own products. This helps guarantee proper performance and lifespan. Also, you'll have an easier time on a tech line or with a warranty should anything go wrong.
Seek out and follow the required break-in procedure for your new clutch assembly. Each manufacturer will vary, but following it is necessary to ensure proper seat-in of the friction material, full performance, and proper heat cycling. Failure to do so may result in premature wear, decreased holding capacity, improper clutch operation, and will void most warranties.
Most any clutch company will be happy to discuss your clutch problems/needs with you over the phone and help you select the right clutch. You shouldn't be too worried about them trying to talk you into an expensive unit that's overkill for your daily driver or weekend toy because they want you to be happy with their clutch and retain you as a loyal customer. Installing a clutch into your truck that's anything other than what you really need can cause everyone involved quite a bit of grief, not to mention money.
Below is valuable reference material from Centerforce for people with three pedals at their feet and anyone thinking about ever owning a truck with a gearbox. Be sure to file this issue into your library of old motors and factory shop manuals should you start "slipping."
Pressure Plate Overheated-Severe Hot Spots
Symptoms:
Clutch slips-does not hold vehicle power
Clutch chatters
Clutch wore out prematurely
Possible Causes:
Improper break-in procedure
Clutch excessively preloaded-improper adjustment
Excessive slipping from driving style
Solutions:
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Adjust clutch pedal freeplay
Follow proper break-in procedure
Evaluate driving style
Worn Diaphragm Spring Fingers on Pressure Plate
Symptoms:
Difficult clutch engagement or disengagement-difficult shifting
Difficulty adjusting clutch pedal freeplay
Clutch slips-does not hold vehicle power
Clutch wore out prematurely
Possible Causes:
Improperly installed throwout bearing
Clutch excessively preloaded-improper adjustment
Solutions:
Replace throwout bearing with correct part and install properly
Inspect transmission guide tube and bearing collar for wear-repair or replace if necessary
Adjust clutch pedal freeplay
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Pressure Plate Drive Strap(s) Bent/Broken/Missing
Symptoms:
Difficult clutch engagement or disengagement-difficult shifting
Noise from clutch
Possible Causes:
Abusive downshifting
Using clutch as a brake to slow vehicle
Missed shifts
Solutions:
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Evaluate driving style-avoid abusive downshifting
Pressure Plate Improperly Balanced
Symptoms:
Vibration from engine/transmission/shifter
Weight system shifted off center
Possible Causes:
Improper flywheel counterbalance
Improper hardware
Clutch improperly balanced
Flywheel improperly balanced
Solutions:
Verify flywheel counterbalance, if equipped
Use proper hardware-shouldered bolts or locating dowel pins to retain pressure plate to flywheel
Replace clutch assembly
Inspect, resurface, and balance flywheel-replace if necessary
Diaphragm Spring Fingers OverTraveled-Hitting Clutch Disc
Symptoms:
Clutch slips-does not hold vehicle power
Difficult clutch engagement or disengagement-difficult shifting
Clutch wore out prematurely
Noise from clutch
Possible Causes:
Clutch excessively preloaded-improper adjustment
Improper pressure plate and clutch disc combination
Improper flywheel step/cup dimension
Solutions:
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Adjust clutch pedal freeplay
Pressure Plate Bent
Symptoms:
Pressure plate won't bolt evenly to flywheel
Difficult clutch engagement or disengagement-difficult shifting
Clutch chatters
Possible Causes:
Pressure plate dropped
Improper flywheel step/cup dimension
Improper hardware used to fasten pressure plate to flywheel
Debris between pressure plate and flywheel
Solutions:
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Use proper hardware-torque bolts to factory specification
Clean surfaces prior to installation
Clutch Disc Hub Springs Loose/Missing
Symptoms:
Noise from clutch
Difficult clutch engagement or disengagement-difficult shifting
Possible Causes:
Clutch disc installed improperly
Transmission misalignment
Abusive upshifting/downshifting
Worn or missing pilot bearing/bushing
Solutions:
Replace clutch disc-install properly
Inspect and resurface flywheel-replace if necessary
Inspect pilot bearing/bushing-replace if necessary
Evaluate driving style-avoid abusive shifting
Clutch Disc Hub Splines Worn Excessively/Hub Spring Pack Cracked
Symptoms:
Noise from clutch
Difficult clutch engagement or disengagement-difficult shifting
Rapid pilot bearing/bushing wear
Possible Causes:
Transmission/bellhousing misalignment
Transmission hung on clutch disc by input shaft during installation
Worn or missing pilot bearing/bushing
Solutions:
Check transmission and bellhousing alignment
Inspect input shaft for wear
Replace clutch disc
Replace pilot bearing/bushing
Support transmission when installing
Clutch Disc Oil Contaminated
Symptoms:
Clutch chatters
Clutch slips-does not hold vehicle power
Clutch wore out prematurely
Possible Causes:
Oil leak from engine or transmission
Solutions:
Repair oil leak
Thoroughly clean bellhousing and release components
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Clutch Disc Overheated/Abused
Symptoms:
Clutch won't release
Clutch chatters
Clutch slips
Clutch vibrates
Clutch wore out prematurely
Possible Causes:
Excessive engine power
Improper break-in procedure
Clutch excessively preloaded-improper adjustment
Solutions:
Adjust clutch pedal freeplay
Replace clutch with upgraded clutch assembly
Inspect and resurface flywheel-replace if necessary
Follow proper break-in procedure
Evaluate driving style
Clutch Disc Bent
Symptoms:
Difficult clutch engagement or disengagement-difficult shifting
Noise from clutch
Possible Causes:
Clutch disc installed incorrectly
Transmission hung on clutch disc by input shaft during installation
Part damaged during shipping
Solutions:
Replace clutch disc
Inspect pressure plate-replace if wear is found
Evaluate transmission installation-support transmission during installation
Clutch Disc Drive Stop Rivets Abused/Worn/Broken
Symptoms:
Clutch wore out prematurely
Noise from clutch
Possible Causes:
Abusive downshifting/upshifting
Side-step launch of vehicle
Solutions:
Replace clutch assembly
Inspect and resurface flywheel-replace if necessary
Evaluate driving style-avoid using clutch to slow vehicle and abusive launching
Clutch Disc Friction Material Cracked/Broken/Missing
Symptoms:
Clutch slips-does not hold vehicle power
Difficult clutch engagement or disengagement-difficult shifting
Noise from clutch
Possible Causes:
Abusive downshifting/upshifting
Side-step launch of vehicle
Improper break-in procedure
Missed shifts
Solutions:
Replace clutch with upgraded clutch assembly
Inspect and resurface flywheel-replace if necessary
Follow proper break-in procedure
Evaluate driving style-avoid abusive shifting and launching
Clutch Disc Hitting Flywheel or Flywheel Bolts
Symptoms:
Difficult clutch engagement or disengagement-difficult shifting
Noise from clutch
Hub spring(s) loose in clutch disc
Difficulty adjusting clutch pedal freeplay
Possible Causes:
Clutch disc installed backwards
Flywheel bolts improper-head of bolt too large
Flywheel worn-improper resurfacing or too thin
Solutions:
Replace clutch disc
Inspect pressure plate-replace if wear is found
Inspect flywheel crankshaft bolts-replace if wear is found or head is too large
Inspect flywheel-replace if improperly dimensioned
Throwout Bearing Installed Backward
Symptoms:
Noise from throwout bearing
Hard and/or pulsating clutch pedal
Difficult clutch engagement or disengagement-difficult shifting
Possible Causes:
Bearing installed incorrectly
Solutions:
Replace throwout bearing-install correctly
Inspect pressure plate-replace if wear is found
Inspect transmission guide tube and bearing collar for wear-repair or replace if necessary
Clutch Assembly Glazed
Symptoms:
Clutch slips-does not hold vehicle power
Clutch wore out prematurely
Possible Causes:
Improper break-in procedure
Clutch excessively preloaded-improper adjustment
Excessive slipping from driving style
Oil leak from engine or transmission
Solutions:
Repair oil leak-if necessary
Thoroughly clean bellhousing and release componentsReplace clutch assembly
Inspect and resurface flywheel-replace if necessary
Adjust clutch pedal freeplay
Follow proper break-in procedure
Evaluate driving style
Clutch Disc Friction Material Chipped/Bent
Symptoms:
Difficult clutch engagement or disengagement-difficult shifting
Clutch slips-does not hold vehicle power
Noise from clutch
Possible Causes:
Clutch disc dropped during installation or removal
Clutch disc not installed using alignment tool
Solutions:
Replace clutch disc
Use care when installing or removing clutch disc
Throwout Bearing and/or Clutch Fork Improperly Installed
Symptoms:
Hard and/or pulsating clutch pedal
Noise from throwout bearing
Difficult clutch engagement or disengagement-difficult shifting
Possible Causes:
Fork and/or bearing installed incorrectly
Clutch excessively preloaded-improper adjustment
Clutch release linkage worn or damaged
Solutions:
Inspect throwout bearing for wear-replace if wear is found
Inspect transmission input shaft collar for wear-replace if wear is found
Inspect pressure plate diaphragm fingers-replace if wear is found
Install clutch fork/throwout bearing correctly
Adjust clutch pedal freeplay
Inspect clutch release linkage-replace if wear is found
