Free Car Repair Advice by Certified ASE Technicians
Troubleshooting
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How Does A Clutch Work?
How Does a Clutch Work?
Introduction
When your car is 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 to make shifting
smoother. The clutch pressure place 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 and
holds the input shaft for the transmission steady.
Clutch and Flywheel Assembly (Cut Away)
Most clutch assemblies operate on the same principle; hold a clutch disc against a flywheel under pressure with the
ability to release the pressure to allow the clutch disc to freewheel. The
clutch disc is connected to the transmission using an input shaft to the
transmission gears and then through to the drive shaft or axles.
Typical Fly Wheel Configuration
When replacing the clutch assembly always resurface the flywheel clutch disc
surface. As the clutch wears it can cause the flywheel surface to become
un-even, much like a worn brake rotor. If a new clutch disc is installed on and
old flywheel it can cause the clutch to not operate properly. If the flywheel is
dual stepped (example shown) it must be machined the same way or the clutch
clamping pressure will be incorrect causing the clutch to slip or not
disengaged.
Typical Clutch Pressure Plate, Disc and Throw-out Bearing
There are two different types of clutch activation methods. Some manufactures
use a cable that is fastened to the clutch pedal and then to the clutch fork.
While other manufacturers use a hydraulic clutch master cylinder that is
connected to a slave cylinder which is positioned at the bell housing, also connecting
to the clutch fork. When the clutch pedal is depressed it will force the clutch
fork onto the pressure plate causing the pressure plate fingers to release the
clutch disc.
Typical Clutch Fork
When installing a new clutch assembly always clean and lube all pivot points
including the input shaft splines and throw out slide surface. Do not use grease
in excess because it can contaminate the clutch disc causing the clutch to grab
and not operate smoothly. Always tighten the clutch pressure plate evenly; never
tighten one bolt at a time because it can cause the pressure plate to warp
inhibiting clutch disengagement. Use a clutch disc alignment tool to center the
clutch disc while the clutch assembly is hand tight. The transmission input
shaft will not allow the transmission to be installed completely if the clutch
disc is not aligned properly.
Typical Clutch Fork, Throw-out Bearing Installation
To replace a clutch disc the transmission must be removed. To perform this
operation a car repair manual is needed because every manufacturer is different.
Basic Step by Step Removal Instruction:
Read Completely Before Beginning
- Raise and support car in a safe and secure manner
- Disconnect the battery (negative side)
- Drain the transmission of fluid
- Remove any obstructions such as exhaust and heat shielding
- Remove driveshaft assembly
- Remove starter assembly (if needed)
- Support the engine as you remove the transmission support member
- Allow the transmission and engine assembly to hang down about 2 to 5
inches. This position allows you to access the upper transmission bell
housing bolts easier.
- Remove all but one bell housing bolts
- Support the transmission as you remove the last bolt
- Remove the transmission
- Remove the clutch pressure plate (note: the clutch disc will fall out
when the pressure plate is removed)
- Remove flywheel to be re-surfaced
- Clean and lube all pivot points including the input shaft splines and
throw out slide surface.
- Re-install flywheel
- Reinstall clutch using a clutch disc alignment tool to center the clutch
disc while the clutch assembly is hand tight. (note: the clutch disc can
only be installed one way, if the disc is in backwards it will cause the
clutch not to disengage) Most clutch disc's have a sticker telling which
side is
the "flywheel side". If not, most common installation is the raise part of
the disc is toward the transmission.
- Tighten the pressure plat evenly to avoid bending
- When re-installing the transmission never allow the transmission to hang
without the mounting bolts. If the transmission is allowed to hang it can
bend the clutch disc causing the clutch not to disengage.
- Finish reassembly and refill the transmission
- Adjust as needed (note: some cars have self adjusting clutched so
readjustment is not required)
For manufacturer specific instructions please consult a
car repair
manual
Troubleshooting Noise and Problems -
Clutch Problem Information
- 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.
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.
Troubleshooting
/
How Does A Clutch Work?
Additional Resources
Check Manufacturer Specific Clutch
Problem Questions and Answers
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