Clutch Operation

Starting the Vehicle in the Proper Gear

An empty vehicle can be started in a higher transmission gear ratio than a partially or fully loaded vehicle. A good rule of thumb for the driver to follow is: select the gear combination that allows you to start moving with an idling engine, or if necessary, just enough throttle to prevent stalling the engine. After the clutch is fully engaged, the engine should be accelerated to the correct rpm for the upshift into the next higher gear.

Gear Shifting Techniques

Many drivers upshift into the next gear, or even skip-shift into a higher gear, before the vehicle has reached the proper speed. This type of shifting is almost as bad as starting off in a gear that is too high, since the engine rpm and vehicle speeds are too far apart, requiring the clutch to absorb the speed difference with friction, creating heat. For transmission operating instructions, see Freightliner SmartShift Shift Control in this manual.

The clutch brake is applied by fully depressing the clutch pedal. Its purpose is to stop the transmission gears from rotating in order to engage the transmission gears quickly in making an initial start.

Excessive Vehicle Overload, or Overloading the Clutch

Clutches are designed for specific vehicle applications and loads. These limitations should not be exceeded.

Riding the Clutch Pedal

Riding the clutch pedal is very destructive to the clutch, since partial clutch engagement permits slippage, generating excessive heat. Riding the clutch pedal will also put a constant thrust load on the release bearing, which can thin out the lubricant. Release bearing failures can be attributed to this type of misuse.

Holding the Vehicle on an Incline With a Slipping Clutch

A slipping clutch accumulates heat faster than it can be dissipated, resulting in early clutch failures. Never use the clutch as a hill holder.

Coasting With the Clutch Released (Pedal Depressed) and the Transmission in Gear

Coasting with the clutch released and the transmission in gear can cause high driven disc rpm through multiplication of ratios from the final drive and transmission.

Engaging the Clutch While Coasting

Engaging the clutch while coasting can result in tremendous shock loads and possible damage to the clutch, as well as to the entire drivetrain.

Reporting Erratic Clutch Operation Promptly

Reporting erratic clutch operation as soon as possible will give maintenance personnel a chance to inspect and lubricate the clutch components, make necessary internal clutch and linkage adjustments, etc.

Clutch free pedal is a decreased resistance felt at the top of the clutch pedal stroke. See Fig.. With the clutch pedal in this range, the clutch is fully engaged and the only resistance to clutch pedal movement is the force of the return spring. If clutch free pedal is 3/4 inch (20 mm) or less, measured at the pedal, have the clutch adjusted.

Free Pedal

Fig. 1, Clutch Free Pedal

Free pedal should be included and commented on daily in the driver's report, since clutch free pedal is the maintenance department's guide to the condition of the clutch and the release mechanism.

See Group 25 of the Century Class Trucks Workshop Manual for clutch adjustment procedures and specifications.

Clutch brake squeeze is an increased resistance (greater than the force of the clutch spring) felt as the clutch pedal approaches the end of its stroke. If the gears grind when shifting into first or reverse gear with the clutch pedal fully depressed, the clutch is out of adjustment or the clutch brake is worn and needs to be replaced.

Clutch Adjustments

Clutches have an internal adjustment, and external linkage adjustment. See Group 25 of the Century Class Trucks Workshop Manual for clutch adjustment procedures and specifications.