On mechanical clutch linkages, free-pedal travel
should be included and commented on daily in the
driver’s report, since clutch free-pedal travel is the
best guide to the condition of the clutch and the re-
lease mechanism.
Clutch Wear
The major reason clutches wear out too soon is ex-
cessive heat. Clutches are designed to absorb and
dissipate more heat than encountered in typical op-
eration. The temperatures developed in typical op-
eration will not break down the clutch friction sur-
faces. However, if a clutch is slipped excessively or
required to do the job of a fluid coupling, high tem-
peratures develop quickly and destroy the clutch.
Temperatures generated between the flywheel,
driven discs, and pressure plates can be high
enough to cause the metal to flow and the friction
facing material to char and burn.
CAUTION
Do not allow sustained slippage of the clutch;
this could severely damage the clutch disc, pres-
sure plate, or flywheel. Damage caused by clutch
slippage due to improper break-in is not warrant-
able.
Slipping and excessive heat are practically nonexist-
ent when a clutch is fully engaged. But during the
moment of engagement, when the clutch is picking
up the load, it generates considerable heat. An incor-
rectly adjusted or slipping clutch will rapidly generate
sufficient heat to destroy itself.
The most important items that a driver should be
aware of to ensure long service life of the clutch in-
clude: starting in the right gear, recognizing clutch
malfunctions, and knowing when to adjust a clutch.
Clutch Adjustments
Some clutches have an internal adjustment. See the
applicable section in
Group 25
of the
Business
Class
®
M2 Workshop Manual
for clutch adjustment
procedures and specifications.
CAUTION
Operating the vehicle with the clutch incorrectly
adjusted could result in clutch or clutch brake
failure.
Clutch Lubrication
The release bearing should be lubricated at frequent
intervals. See
Group 25
of the
Business Class
®
M2
Maintenance Manual
for intervals and procedures.
CAUTION
Failure to lubricate the release bearing as recom-
mended could result in release bearing damage
and damage to the clutch.
NOTE: The Sachs hydraulic clutch does not re-
quire lubrication of the release bearing.
Sachs Hydraulic Clutch
The Sachs hydraulic clutch is a 14.5-inch (365 mm)
push-type clutch that is used with the Mercedes-
Benz medium-duty transmissions, models MBT520
and MBT660.
NOTE: All Mercedes-Benz transmission models
require a hydraulic clutch system. For more in-
formation on the Mercedes-Benz transmissions,
see under the heading "Mercedes-Benz Manual
Transmissions."
The clutch hydraulic system consists of three main
components:
•
A pedal unit, including the pedal, master cylin-
der and fluid reservoir,
•
A slave cylinder at the clutch,
•
A hydraulic hose that connects the master and
slave cylinders.
Keep the clutch fluid reservoir full to the MAX mark.
If fluid level falls below the MIN mark, have the hy-
draulic system checked for leaks at an authorized
Freightliner service facility. Use only DOT 4 brake
fluid to fill the reservoir.
The hydraulic clutch provides smooth, quiet, and reli-
able clutch actuation with a minimum of mainte-
nance.
Pressure builds up in the master cylinder when the
clutch pedal is pressed. This pressure is transmitted
through the brake fluid in the hose to the slave cylin-
der, where it acts directly on the clutch release fork.
Drivetrain
8.2
