Diagnosing a Slippping Clutch

Updated on May 2, 2019
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

A clutch assembly.
A clutch assembly. | Source

A slipping clutch may show one or more of the following symptoms:

  • No engine power: You notice engine poor performance when power is required as you drive uphill or pull a trailer.
  • Fast clutch pedal action: Once the clutch disc begins to wear down and slip, you'll notice that pressing the clutch pedal lightly is all you need to engage or disengage the clutch.
  • Burning odor: This odor comes from the friction material on the clutch disc rubbing against the flywheel and pressure plate. Instead of grabbing, the clutch facing slips, rising its temperature.
  • High engine speed: You notice that engine revs high when shifting gears or going uphill.

It's a good idea to pay attention to these symptoms and diagnose the problem as soon as possible. A clutch slipping will eventually prevent your engine from transferring rotating power to your driving wheels and leave you stranded in the middle of the road.

A slipping clutch may appear on:

  • high mileage engines
  • vehicles driven mostly in heavy traffic
  • non-self-adjusting systems that require periodic maintenance
  • vehicles with a newly installed clutch

The next sections briefly explain how the clutch works, what is a slipping clutch, what are the main causes for it, and an easy test you can apply at home to diagnose a potential slipping clutch.

A standard clutch disc.
A standard clutch disc. | Source
Index
1. How the Clutch Works
2. What is Clutch Slippage?
3. What causes clutch slippage
4. Clutch Slippage Test
5. A Slipping Clutch is a Warning Sign

1. How the Clutch Works

The clutch disc mounts on the transmission input shaft. It is located between the flywheel and the pressure plate. The flywheel is mounted on the engine's crankshaft, while the pressure plate is attached to the flywheel.

It is the rotating movement of the flywheel and pressure plate that transmits rotating power to the transmission when the clutch disc is pressed between the flywheel and pressure plate.

The friction material on the clutch face allows the clutch to grab to the flywheel and pressure plate to do its job. When the clutch's friction material is too worn, or a mechanical problem prevents the pressure plate and flywheel to grab onto the clutch disc, a clutch-slippage condition develops. Watch the video above to get a much better visual reference for how the clutch operates.

A clutch pedal in need of adjustment may cause clutch slippage.
A clutch pedal in need of adjustment may cause clutch slippage. | Source

2. What is Clutch Slippage?

Basically, a slipping clutch happens when you depress the accelerator, the engine revs up, but the car hesitates to move. Your vehicle may move slowly through some gear ranges too, depending on the severity of the problem. You may feel the clutch slipping:

  • as you accelerate from first gear
  • during driving in higher gears.
  • going uphill or while pulling a trailer

Clutch slippage is a safety issue, and it can lead to a serious road accident.

3. What causes clutch slippage

External or internal mechanical problems can lead to a slipping clutch.

External issues may include:

  • Cable or linkage system problems like binding, broken or bent parts in the assembly.
  • Clutch in need of adjustment (throw out bearing pushing against the pressure plate).
  • Rust, damage, or misalignment causing binding in the release mechanism.
  • Damaged motor mount: Under load, engine movement can push against the clutch release fork, or cause clutch linkage to bind.
  • Leaking master cylinder or slave cylinder on a hydraulic system type (the clutch may also fail to disengage and the pedal may become soft).

Internal issues may include:

  • Clutch disc worn out.
  • Clutch disc contaminated with oil (oil seal leaking).
  • Worn flywheel surface.
  • Weaken-worn out pressure plate diaphragm springs.
  • Leaking front transmission seal (main input shaft).

Inspect first for external problems that might be affecting the release mechanism. If everything seems to be fine, then you may need to drop the transmission to check the clutch assembly.

Damaged engine mounts can also lead to clutch slippage.
Damaged engine mounts can also lead to clutch slippage. | Source

4. Clutch Slippage Test

Often, you can tell the clutch is slipping just by driving the car around and engaging the different gears. If you have a repair manual for your car model, you may find a testing procedure for your particular configuration. But you can also apply these general steps.

First, check clutch pedal play:

  1. Position a tape measure or ruler next to the clutch pedal. The end of the ruler should rest on the floor.
  2. Push the pedal with your hand, just enough to take out pedal slack.
  3. If the pedal moves between one and two inches, pedal play is within an acceptable range. Continue with the following steps; if you feel there's little pedal play, you may need to manually adjust the clutch, or the clutch has worn out and you need to replace it. If necessary, consult your vehicle repair manual.

If you don't have the manual, you can buy an aftermarket copy through Amazon. Haynes manuals come with step-by-step procedures for many maintenance, parts replacement, and troubleshooting tasks. So you'll save a lot of money by doing many of these projects at home.

Check clutch for slippage:

  1. Find a safe, level place to park your vehicle with plenty of space in front of it to allow your car to move forward, if necessary.
  2. Engage the parking brake.
  3. Start the engine and let it idle.
  4. Fully depress the clutch pedal to disengage the clutch.
  5. Shift your transmission into third gear.
  6. Accelerate the engine up to 2000 rpm.
  7. Slowly release the clutch pedal to allow the clutch to engage.

    • The engine should stall as soon as the clutch is fully engaged (locks up).
    • If the engine runs for a few seconds before stalling, the clutch could be partially slipping.
    • If the engine continues to run after releasing the clutch pedal, the clutch is slipping.
  8. Shut off the engine three to four seconds after fully releasing the clutch pedal to prevent damage to the pressure plate or flywheel.

A worn out clutch disc may cause slippage.
A worn out clutch disc may cause slippage. | Source

5. A Slipping Clutch is a Warning Sign

Clutch slippage is a safety issue, and it can lead to a serious road accident. Take your slipping clutch as a first warning sign. Eventually, your vehicle will stop moving, perhaps in the middle of the road, once the flywheel and pressure plate are unable to grab onto the clutch disc.

If you followed the test steps described here, and you suspect a slipping clutch, have the clutch diagnose by a qualified shop and, if necessary, install a new clutch kit.

Driving a vehicle with a slipping clutch can cause a serious accident.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

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    © 2019 Dan Ferrell

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