Help and Support Centre - Proper Clutch Control
Clutch control refers
to the act of controlling the speed of a vehicle with a manual
transmission by partially engaging the clutch plate, using the
clutch pedal instead of (or in conjunction with) the accelerator
pedal. The purpose of a clutch is in part to allow such control;
in particular, a clutch provides transfer of torque between
shafts spinning at different speeds. In the extreme, clutch
control is used in performance driving, such as starting from a
dead stop with the engine producing maximum torque at high RPM.
Clutch control also applies to driving a tractor.
With the clutch pedal
completely pressed, there is no direct link between the engine
and the driveshaft, so no power can pass from the engine to the
driveshaft and wheels. With the pedal entirely released, there
is full contact between the engine and the driveshaft, via the
clutch plate, which means that the engine can apply power
directly to the driveshaft. However, it is possible to have the
clutch plate partially engaged, allowing the clutch to slip. As
a result, only a fraction of the power from the engine reaches
Balancing the clutch
Normally, when a vehicle is stationary on an uphill slope it is
necessary to use the handbrake in conjunction with clutch
control to prevent the vehicle from rolling backwards when
pulling away. However, in situations where the vehicle must be
stopped briefly, for example when negotiating tight turns, the
clutch can be used to balance the uphill force from the engine
with the downhill force of gravity. The benefit of this is that
there is no need for the hand- or foot-brake, and the driver can
pull away more quickly. Using this technique will, however, wear
out the clutch faster.
Potential clutch problems
Even normal use of clutch control increases the wear (and
decreases the lifespan) of the clutch. Excessive use of clutch
control or riding the clutch will cause further damage.
While the use of clutch control at low speed can be used to
obtain greater control of acceleration and engine braking, once
a vehicle has picked up sufficient speed the clutch should be
fully engaged (pedal released).
Excessively revving the engine while using clutch control, or
keeping the clutch partially engaged while accelerating with the
gas pedal, can cause unnecessary damage to the clutch.
Riding the Clutch
In a vehicle with a
manual transmission, such as a tractor, riding the clutch refers
to the practice of needlessly keeping the clutch partially
disengaged. This results in the clutch being unable to fully
engage with the flywheel and so causes premature wear on the
disc and flywheel.
melted and seized thrust bearing (Fig 1) and melted
clutch fingers (Fig 2) - a direct result of riding the
clutch pedal - the constant pressure on the thrust
bearing caused it to overheat, melt and finally seize.
thrust bearing then melted the fingers on the clutch
itself as shown.
common example of riding the clutch is to keep slight continual
pressure on the clutch pedal whilst driving, as when a driver
habitually rests his/her foot on the clutch pedal instead of on
the floorboard or dead pedal.
Although this slight
pressure is not usually enough to allow the clutch disc itself
to slip, it is enough to keep the release bearing against the
release springs. This causes the bearing to remain spinning,
which leads to premature bearing failure.
When shifting properly, the driver "shifts" to another gear and
then releases pressure on the clutch pedal to re-engage the
engine to the driveshaft. If the pedal is released quickly, a
definite lurch can be felt as the engine and driveshaft
re-engage and their speeds equalize. However, if the clutch is
released slowly the clutch disc will "slip" against the
flywheel; this friction permits the engine a smoother transition
to its new rotation speed. Such routine slippage causes wear on
the clutch analogous to the wear-and-tear on a brake pad when
stopping. Some amount of wear is unavoidable, but with better
clutching/shifting technique it can be minimized.
Riding the clutch occurs when the driver does not fully release
the clutch pedal. This results in the clutch disc slipping
against the flywheel and some engine power not being transferred
to the drive train and wheels. While inefficient, most drivers
routinely use this technique effectively when driving in reverse
(as fully engaging the reverse gear results in velocity too
great for the short distance travelled) or in stop-and-go
traffic (as it is easier to control the throttle and
acceleration at very slow speeds).
Riding the clutch should not be confused with "freewheeling" or
"coasting", where the clutch is pressed down fully allowing the
vehicle to roll either downhill or from inertia. While this is
not damaging to the vehicle, it can be considered a dangerous
way to drive since one forgoes the ability to quickly accelerate
if needed. It is, however, a common practice to roll into a
parking space or over speed bumps via inertia.
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