Troubleshooting / Why Does My Clutch Not Work Sometimes?

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Why Does My Clutch Not Work Sometimes or Not at All?

Introduction

When you are stopped or coming to a stop the engine needs to be disconnected from the transmission or the engine will stall. With automatic transmission vehicles a torque converter is used to separate the two units, but with manual transmission vehicles a clutch assembly is used to do the job. This clutch kit or unit is composed of a clutch disc, pressure plate, throw out and pilot bearings. (Some front wheel drive vehicles do not use a pilot bearing). Both types of vehicles use a flywheel but are designed a little differently. An automatic transmission has a lighter weight unit that the torque converter bolts directly to and is sometimes referred to as a flex plate. A manual transmission flywheel assembly is made heavier to help engine inertia and make shifting smoother. The clutch pressure plate bolts to the flywheel trapping the clutch disc in-between. The throw out bearing presses against the pressure plate to engage and release the disc. The pilot bearing is mounted in the flywheel or the end of the crankshaft and holds the input shaft for the transmission steady. Below we have created a guide to aid the diagnoses and repair procedure for most common clutch problems.

Clutch and Flywheel Assembly (Cut Away)

READ COMPLETELY BEFORE BEGINNING!

Car Repair Guide

• Problem Set 1 - Transmission will intermittently not go into gear:
   
  • Check the Clutch Fluid - Some cars are constructed with a hydraulic clutch system. This means there is brake fluid that is used as hydraulic fluid to operate the clutch actuation system. Check the fluid level; if the fluid is low or gone you may have a leak. The clutch actuation system will not work without fluid. Inspect the clutch master and slave cylinder for leakage. (Note: inspect under the dash toward the rear of the clutch master, it is common for a leak to occur here).
     
    
  • Clutch Disc Failure - The clutch disc could be completely broken not allowing the disc to "slip" within the pressure plate and flywheel. The transmission must be removed and the clutch assembly dissembled to inspect for this condition.
     
  • Internal Transmission Damage - The transmission utilizes an input shaft to drive the remaining gears inside the transmission. If this input shaft or gears fail it can cause the gear shifter to move but no output to the differential. The clutch operation will work normally in this condition.
     
  • Failed Clutch Master Cylinder - Some vehicles are equipped with a clutch master cylinder that transforms your foot pressure to hydraulic pressure. The clutch master cylinder forces brake fluid into a slave cylinder that actuates the throw out bearing which disengages the clutch assembly. If the clutch master cylinder fails it will not operate the clutch slave cylinder and in turn not disengage the clutch assembly, the clutch pedal operates but the transmission will not go into gear.
     
  • Broken Clutch Cable - Some vehicles are equipped with a clutch control cable instead of the master and slave cylinder. If the clutch control cable fails it will not actuate the clutch assembly causing the transmission to not go into gear. If you push the clutch pedal and it feels like it's not doing anything inspect the clutch cable for breakage.
     
  • Broken Clutch Fork Pivot - If the clutch actuation method checks out ok (cable or hydraulic) you could have a clutch pivot that has failed. This pivot is used to transfer force from the clutch actuation system to the clutch throw bearing and in turn depress the clutch pressure plate releasing the disc. If this pivot fails it will cause the clutch to not disengage, to check for this problem the transmission will have to be removed in most cases.
     
  
  
• Problem Set 2 - Transmission goes into gear but it feels like its slipping
  
  
  • Check the Clutch Disc - The clutch disc is made of an asbestos compound much like a brake pad, as this material wears it loses pressure against the pressure plate and flywheel. When this normal wear condition occurs the clutch disc will start to lose positive contact and give the driver a slipping sensation. This can mean one of two things, either the clutch is out of adjustment or the clutch disc is worn out and replacement is needed. (Note: if the engine is leaking motor oil from the valve covers or rear main seal it can contaminate the clutch disc causing it to slip)
    
    Best Practices: When replacing a clutch disc always replace the pressure plate throw out and pilot bearing if equipped (clutch kit) and remove the flywheel and have it resurfaced.
     
  
  
• Problem Set 3 - Transmission makes grinding noise while in operation or shifting gears
   
  
  • Transmission Internal Bearings - The transmission inside your car depends on many roller and thrust bearings to support the shafts and gears that make up the transmission. If any of these bearings fail it will cause the transmission to make a grinding or whirring sound. If a gear synchronizer (synchro) is worn it will not stop the gear when shifting and will cause a grinding inside the transmission when the rotating gears attempt to mesh. If either of these conditions has occurred the transmission will have to be replaced or disassembled and repaired.




• Troubleshooting Noise and Problems

  • If the vehicle is running and a whirring sound is heard and then it goes away when the clutch is depressed, the transmission input shaft bearing has failed.
     
  • If the transmission is quiet in neutral but when you depress the clutch a squealing noise is observed, a clutch throw out bearing has failed.
  
  
• Tip 1:  Never let little noises go unattended; a small noise can cause a large problem and transmission operation failure. Never overload a vehicle or tow beyond the capacity this can cause premature transmission failure.
   
• Tip 2:  Cars with automatic transmissions are equipped with a torque converter that when it fails will cause the engine to stall, but only when you put into forward or reverse gear.

For exact specific repair procedures for any of the steps above visit our online repair manual page.

WARNING! Always have the vehicle under inspection on level ground, in park with the emergency brake on. Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when anyone is near the battery or engine. Always have an operational fire extinguisher close by, obey all first aid instructions in the event of an accident. Never stand in front or behind a vehicle when cranked over or running. When engine is cranked over keep hands and clothing free from rotating components.

Additional Resources

• Why does my engine stall at idle?
• How do I change my spark plugs?
• Why does my engine crank over but not start?
• Why wont my engine crank over?
• How do I test the engine ignition system?
• Why does my engine over heat?

Troubleshooting / Why Does My Clutch Not Work Sometimes?

• Purchase Clutch Parts

Check Manufacturer Specific Clutch Problem Questions and Answers

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