Complete Guide To Using An 18 Speed Transmission

When you think of driving truck, what is one of the first things that comes to mind? For many of us, it’s shifting gears. When you talk to long time truck drivers, one of the first things you’ll learn is what kind of transmission is in their truck. Make of truck, model, engine, and then transmission. You will hear various opinions as to which is best, but in order to give an educated opinion, you need to know the differences.

Our focus in this article is the 18 speed transmission. When you hear 18 speed, you may have some questions. A really good way to learn is to ask the right questions.

Questions, such as:

  • What is an 18 speed transmission?
  • How does an 18 speed compare to the most popular transmissions?
  • What is the optimal gear pattern and gear ratios?
  • What loads typically use this type of gear pattern?
  • What are the pro/cons?
  • Is this a good transmission for beginners?
  • How do you shift?

Let’s answer these questions one at a time.

What is an 18 speed transmission?

It may sound like an obvious answer, but that’s not really the case. In a typical 18 speed transmission, you can split every gear. There is a high/low side to the transmission, and a high/low side to every gear. The following image shows an example of an 18 speed shift pattern. You will notice that there is a high/low side to every gear, including reverse and the Lo gear.

2. How does an 18 speed compare to the most popular transmissions?

There are many options for transmissions in trucks. You have 8, 9, 10, 13, 15, and 18 speed transmissions. The choice of transmission is largely dependent on personal preference. The most popular is probably the 10 speed. A 10 speed is very easy to learn, and easy to shift. They also stand up well to abuse by those learning to drive. As a result, many companies prefer 10 speeds. But for experienced drivers, an 18 speed transmission is usually preferred.

The biggest difference is the amount of shifting you’ll have to do. The beauty of an 18 speed is the
ability to split every gear. You won’t need to use most of the gears most of the time. But having options under a variety of situations is something to appreciate.

3. What is the optimal gear pattern and gear ratios?

The gear pattern in the image above is a pretty standard gear pattern for an 18 speed transmission. When driving an 18 speed, you will usually not need to use each gear. Unless the load is very heavy, you can start in a higher gear. And when empty, I would usually start out in the high side of 3rd or 4th gear. Also, you wouldn’t have to split every gear when shifting up through.

The optimal gear patterns and ratios depend alot on where you’ll be running your truck  the most. If you are going to be running through flat land/terrain most often, then a lower gear ratio would be more useful, something like a 2.93 or 3.08. That gear ratio is a good option for higher cruising speeds on the highway.

For more variety in terrain, with hills and mountains, you may choose to go with a 3.55 or 3.73, which will give you good  top-end as well as plenty of pulling power. So in order to choose the best combination, you’ll need to consider a few things: average load weight, where you’ll be running the most, and what is most important to you; fuel economy, pulling power, and/or top-end speed.

4. What loads typically use this type of gear pattern?

You can use an 18 speed transmission effectively with any type of load. However, you will really appreciate having an 18 speed if the loads are heavy and the terrain is hilly or mountainous. The draw to an 18 speed is the ability to split every gear. As you start from a stop, having the ability to shift every half of a gear is a huge plus. It will seem like you never stop shifting, until you get into your running gears. That’s when the real benefits kick in.

5. What are the positive aspects of having of an 18 speed?

We already mentioned some of the positives above in this article. One of my favorite things about an 18 speed is when pulling hills. In my driving career, I did most of my driving in Pennsylvania. Even those just beginning their driving career, know something about Pennsylvania; there are lots of hills and mountains when driving the interstate highways. The beauty of an 18 speed really shows up when travelling through the hills and mountains of any state. The ability to split every gear really comes in handy, and really spoils you as a driver.

Have you ever been pulling a really steep hill, with a really heavy load, and you realize you need to downshift? As a new driver, what goes through your mind? Have you ever been hesitant to shift, afraid you might not be able to hit the next gear? Have you ever seen drivers stopped in the middle of hills, having to start out over again, because they missed a gear? No one wants to be that guy.

With an 18 speed, and the ability to split every gear, the likelihood of being that guy decreases. And if you have the right rears, you can climb even some of the toughest hills while only splitting your top gear. In my opinion, that is one of the biggest positives to an 18 speed.

6. Is this a good transmission for beginners?

I believe that any driver can be adept at shifting any transmission with the proper training and practice. It can seem intimidating at first, but once you learn to drive an 18 speed, you may not want anything else.

7. How do you shift?

Look again at the shift pattern image below. Learning to drive an 18 speed sounds  harder than it really is. I would always start in 3rd or 4th gear. When starting out, I wouldn’t split the gears on the low side. I would wait to start splitting gears until I was in the high side of the transmission. There are also times that you may choose not to split any gears, until you are at your top running speed on the highway.

18 speed transmission

For example, you can start in gear 3L; that is with your range selector in the down position and your splitter in the backward position. As you shift through the gears, you can leave your splitter selector in that backward position, even after you switch your range selector into the upward position and shift into the high side of the transmission.

When you reach top speed on the highway, you can choose to slide your splitter selector forward, thus putting the transmission into its highest gear. Be sure to switch your range selector and your splitter selector before switching to the next gear.

It may sound complicated, but it really isn’t. The next time you have the option to choose, go with the 18 speed transmission. With the right gearing and rear end ratios, you won’t regret it. And you won’t ever want to shift another transmission.

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