Best diesel techs are good in the clutch
Training on transmissions is a must
By Aaron Bereiter
When shopping for a car, one has numerous options: make, model, color, two doors, four doors, manual or automatic transmission, and much more. When selecting a heavy duty truck, coach or bus, there is one element that is removed from that equation: transmission. Medium and heavy duty vehicles require manual transmissions to allow operators greater control when driving in a variety of conditions, whether it’s uphill, highway or residential streets. But what would the transmission be without the clutch? Training on clutches is something all reputable diesel technicians should complete.
Why is the clutch so important? The clutch allows for a smooth connection and disconnection of engine torque to the
transmission input shaft. This connection and disconnection happens every time the vehicle starts from a stop, up-shifts and down-shifts, and results in smoother stops and starts. Many modern heavy-duty diesel vehicles employ a Pull Type clutch, which means that when the clutch is depressed, the release bearing moves away from the engine.
Pull Type clutches can be used with both synchronized and non-synchronized transmissions. If used with a non-synchronized transmission, a clutch brake will be part of the overall system to prevent “gear clash” when shifting from neutral to reverse or a forward starting gear. There are two basic types of clutch brakes: Solid and Overrunning. It is important to know what type of clutch your vehicle houses, in addition to whether or not you have a clutch brake installed.
A scenario where this becomes important is if you were to push the clutch pedal all the way to the floor in a vehicle with a clutch brake while the vehicle is moving. If this happens in a vehicle equipped with a Solid clutch brake, the two small tabs on the input shaft will be sheared off and render the clutch brake inoperable. An Overrunning clutch brake will slip internally and prevent damage to the brake.
Another important element within clutches is the clutch linkage. There are three main types of clutch linkages: mechanical, cable and hydraulic. Mechanical clutch linkages are made up of rods, clevices, bell cranks and levers. Pivot points have a tendency to wear in mechanical linkages, so lubrication is important to prevent extra free play in the clutch linkage. Cable clutch linkages are a cable and pulley system that is connected from the pedal to a lever at the transmission. The cable housing must be mounted securely, as cables can seize up due to corrosion. Hydraulic clutch linkages are becoming increasingly popular, housing a clutch master cylinder with a reservoir that creates the flow into a closed circuit to create pressure. The clutch slave cylinder then uses the pressure to push against the lever on the clutch fork.
Knowing that clutches and transmissions work together, it is important to consider the clutch when removing the transmission. When removing the transmission from the clutch, take the time and care to ensure the clutch discs are not damaged or distorted. Only after the transmission has been completely disconnected and is properly supported with a transmission jack should you remove the bellhousing bolts. In some vehicles, the engine may also need to be supported before the transmission can be removed.
Power trains, not surprisingly, are vital to the operation of heavy-duty vehicles. Knowing the ins-and-outs of transmissions and clutches allows for better maintenance and repair, so make sure the technician working on your vehicle or fleets is well-versed in these areas.
Would you like to employ a qualified diesel technician? UTI is the country’s premier provider of technician training for students seeking a rewarding career in the automotive, diesel, collision repair, motorcycle, and marine industries. To learn more about how you can create long-lasting careers for skilled diesel technicians, call (866) 819-9406 or visit www.uti.edu/employers.
Aaron Bereiter is an ASE Master Technician and Technical Team Leader at the UTI-Chicago campus, located in Glendale Heights, Ill. You can contact Aaron at firstname.lastname@example.org.