CONTENT: This Trucking Handbook walks you through the process of starting first a gasoline, then a diesel truck engine. Next, it shows you two ways of testing a tractor- trailer hook-up and how to put the vehicle into motion. We do this to give you an idea of how to go about starting a heavy-duty truck, but in actual fact, every truck engine is different. When- ever you set about teaching others how to start a truck engine and put it into gear, you risk oversimplification.
Whenever a driver attempts to start a truck from a stopped position, there are a number of factors to be taken into consideration. What type of engine is in the truck or tractor? Is it a gas engine or a diesel? Is it an in-line six cylinder or a V8? Is it empty or hauling a full load? What is the rig's gross weight? What kind of road surface is the rig on? Is the ground level or hilly? The answer to each of these questions has a bearing on how easy or hard it will be to make a smooth start.
The overall gear ratio is the most important factor for easy starts and eliminating clutch, drive line and axle abuse, but each of the items we have mentioned has a bearing on how easy or hard it will be to make a smooth start.
Considering all of the above, the responsibility for making a smooth start still rests with the driver unless there is something mechanically wrong with the unit. Even then, part of the responsibility still rests with the driver. Remember, you are not always going to drive a new truck, nor is your truck's maintenance always going to be in your hands. It's up to you to know what to do, even when faced with a mechanical malfunction.
One of the major problems a new driver faces is coordination of clutch and throttle when starting a truck. This is because clutch action and throttle use varies greatly from one rig to another depending upon the type of unit you are driving, road conditions, etc., as we mentioned above.
That's why we tell drivers all the time: ease into a new situation. Don't just jump into the driver's seat and take off. Take your time. Get a feel for the rig and the gear box you're driving.
What's right for one engine is not necessarily right for another. With a 350 hp Cummins diesel engine, you want to ease out the clutch in your starting gear and let the engine governor pick up the slack until the rig starts to move. Then you want to ease down on the throttle. A gas engine with a loaded trailer, however, will stall the engine using this method.
All starting situations are not the same. Take a moment to think before you go popping a clutch out. If you don't, you can easily break an axle, "U" joint, or drive line. DON'T POP THE CLUTCH. And don't try to hold a truck on a hill by riding the clutch. The same thing applies to stops at traffic signals. Don't sit there with your foot on the clutch and throttle; you're liable to scorch the clutch plate and discs, greatly increasing the chances of it slipping or completely failing.
Just like people, each truck you drive will handle differently, so get to know your engine before making any fast moves. The normal, well- adjusted clutch pedal will have about six or seven inches of travel from point to point. Usually the first one and a half or two inches will be what we call "free play," meaning that you will feel no pressure from the pedal in this area. Action from the pressure point down through the next six inches or so will disengage the clutch for shifting. The last one and a half inches to the floor board or end of the travel will engage the clutch brake on the shaft. (Remember, these are just guidelines. The clutch-pedal travel will vary from truck to truck.)
Don't engage the clutch brake every time you use the clutch. In other words, don't use that last one and a half inches each time you engage a gear. Use it only to engage your starting gear and reverse gears. Here's why: The clutch brake consists of a couple of fiber discs and a steel disc mounted on the transmission shaft. The transmission shaft goes through the clutch and ends up in the engine fly wheel pilot bearing. When you press down all the way on the clutch pedal, you are pulling back on the clutch release bearing or throw-out bearing. The clutch release bearing squeezes the discs between the release bearing and the front of the transmission case, thereby stopping the transmission shaft so that you can put the transmission into the starting gear without either a pause or a lot of grinding.
That's all pretty technical, but what it means is simply this: Engage the clutch brake only when engaging your starting and reverse gears. If you use the clutch brake all the time, you will wear it out and won't have it when you need it. If you find that your clutch brake is not working well, you may want to have it looked at. It could be worn out from constant use or it could be out of adjustment.
Proper and Improper Clutching Techniques
If you have the opportunity of riding with other drivers, as time goes by you will realize that your training helped you avoid some of the bad habits that self-taught drivers have picked up over the years. One of the worst habits is "jack rabbit starts." Another is just the opposite: high range starts with a Roadranger transmission. The latter usually occurs because the driver is too lazy to shift through the appropriate starting gears. Both of these bad habits are hard on equipment.
We could go on for pages and pages about improper shifting and clutching techniques, but let's stop there and take a look at some rules of thumb for starting both diesel and gasoline rigs.
CAUTION: Whenever you start a rig from a parked position, always hold the rig with the service (foot) brake as you release the parking brake. The rig can move in either direction as you release the parking brake unless you are holding it with the foot brake. When a big rig starts rolling, it is easy to become disoriented and think that a stationary vehicle beside you is the one doing the rolling when it is actually your rig. Drivers have been crushed between vehicles that accidentally rolled unexpectedly backward or forward. And don't forget: Whenever you park, immediately apply your parking brake.
DO: Team up with other members of your class to study methods of shifting and clutching various diesel and gasoline truck engines. (There should be at least four groups.) Each group should be assigned either clutch operation or gear shifting for a particular manufacturer. Suggestions: Group One - Spicer clutches; Group Two - Fuller transmissions; Group Three - Spicer transmissions; Group Four - Clark transmissions. One member of each group should go to the nearest truck dealership and pick up brochures either explaining clutch operation for the assigned engine or giving the shifting specs (i.e., the RPM spread between gears) on the assigned transmissions. Explanations will be given in sales brochures probably available in the sales showroom area.
In your group, study and discuss your topic: either smooth clutch operation or smooth gear shifting. When you feel you understand how the assigned operation is handled on your assigned engine, present this information to the other class groups. When you have made your presentation and listened to the presentations made by the other groups, discuss how starting one engine differs from starting another.
Since methods will vary for each engine, this exercise will give you a good understanding of how operation of one vehicle differs from operation of another. It will also provide you with the most up-to-date information on clutching and gear-shifting available, as you will be working from newly published information direct from the manufacturers.