A few of you blog stalkers have asked about work from time to time. As most of you know, I drive charter buses in Provo, which takes me to a variety of destinations throughout the western United States. The thing that always gets questions is when I mention that some of our older buses have manual transmissions. Needless to say, driving a manual bus is quite different from a car with a manual transmission!
As many of you know, when you drive a car with a manual transmission, you give it a little gas, put it in first, and then let the clutch out to get the car going. As you accelerate, you shift gears by putting the clutch in, moving the shifter the the appropriate gear, and then letting the clutch out. It is all very simple. To explain the exact mechanics behind all this would take a long time, and be pretty boring reading without pictures. If you want all the details, go to www.howstuffworks.com and look it up! (They have pictures!) The reason it works that easily in a car is because of devices on every gear called synchronizers. For the gears to be able to engage, the wheels and internal parts on the transmission must be spinning the same speed. When you change gears, going up, your engine, and there fore transmission, are turning fast. When you push the clutch in to change gears, the engine slows down, but it is no longer connected to the transmission, so the internal parts of the transmission could continue spinning at about the same speed, until they eventually slow down on their own. However, as you stick it in the next gear, the synchronizers slow it down faster, to match the speed of the wheels for the new gear, allowing the gears to line up perfectly. Then you engage the clutch again, and you are off, in a higher gear. Everything I just explained is true in a car, but only kind of true in a bus.
Buses have double clutch transmissions. This means, if you want to get going, it is almost the same. While you are stopped, you push the clutch, and then move the shifter towards first. However, it will not go into gear. There are no synchronizers to help line everything up. Since your engine was turning, the internal parts of the transmission are still turning, until they eventually slow down. They wheels however are not moving, and without the synchronizers, you just have to wait until the transmission parts slow to a stop. Until then, it will not go into gear. But it will make an awful grinding noise while you try to force it! So after a few seconds, you get it into gear. Just like in a car, you let the clutch out slowly and you begin to roll, but then it is time to change gears so you can go faster. This is where things get a little tricky. You push the clutch pedal, and pull it out of first gear. The engine is revved really high, but it has to slow down to get into the next gear. Consequently, the transmission parts are also revved really high, but need to slow down to get into the next gear, but the synchronizers don't exist to help. So, once out of gear and in neutral, you let the gas off, and you let the clutch out for just a second. This slows the transmission down quickly. Then you push the clutch in again and stick it into gear. If you did it right, it goes smoothly into the next gear. If not, it grinds, shakes, lurches, and basically tells you and everyone on board that you did it wrong! This pattern of clutch-shift out of gear-unclutch-clutch-shift into gear-unclutch should last maybe a second, which means you are moving fast. But you have to be gentle, then at least if you do goof it up there will be quieter grinding, less violent shaking, and and minimal lurching.
Down shifting is where things get really tricky. This is partly because there are three pedals on the floor, and you only have two feet, but you really need to be using all three. Since you cannot possibly hit all three pedals just the way you need to at one time, you sort of end up doing a crazy hectic down shifting dance in your seat. As you get to the speed where you need to down shift, you push in the clutch, and pull the shifter out of gear, as usual, and then let the clutch back in. Before you can put it in the lower gear however, everything needs to get going faster, so you rev the engine as fast as it will go. Once it is revved, you step on the clutch and put it in the lower gear, then release the clutch. However, while you are stepping on the gas to rev the engine, you cannot be stepping on the brake to slow down, so hopefully you planned a bit of extra space for this! Once again, if it was done right, and at the proper speed, it is nice and smooth. If not, a few things could happen. If you did it while going too slow, and somehow managed to get into gear anyway, when you let the clutch out, the bus suddenly surges forward. If you were still going too fast, and somehow managed to get it into gear, then it suddenly grabs you and slows you down in a hurry when you let the clutch out. Usually though, it just doesn't go into gear. And then you sit there wondering what to do next because you have slowed down enough that going back to the gear you started in an option. You have to find a gear somewhere. So then you start looking for a gear, but they all grind and shake and nothing seems to be working. Then you wish you had planned that down shift a bit better, but it is too late to think about that. Then, as you are drifting along in no gear, traffic begins to move again, so you have to find a gear to get going. It is either that or coast to a stop in the middle of a busy road!
Why is it this way? Well it all boils down to those little metal pieces called synchronizers. In a car, they make everything go the right speed so you never have to think about it. Buses, and trucks for that matter, simply don't have them. They would have to be so big to be effective that they are not practical, which means the driver is responsible for synchronizing everything. It is a pretty tricky operation when you thing about it. You are trying to get a few little teeth 40 feet away to line up just right, which you cannot see at all. Not only that, they are spinning anywhere from 500 to 2500 rotations every minute!
Now, I am sure you are wondering what exactly happens when you do mess it up, besides the grinding, shaking, and lurching. There are a few ways to fix it. When you are shifting up, if you miss the gear, you can try again, but if you cannot get it into gear within a few seconds, chances are you will not get it in after that. You will lose too much speed. So, if you miss the gear you try again, once, and then you let the clutch back out, rev the engine, and then go back to the gear you started in. You stay there until you are back up to shifting speed, and try again. Some gears are more stubborn than others, and sometimes, even though you nail the speed, it still takes a few tries. If it just will not go, one thing you can do is get off the clutch, and then rev the engine just a little. Then step off the gas, put the clutch in, and quickly stick it into gear. Usually doing that will help it find the gear, but it has to be done very quickly to work. When down shifting, if you mess it up and cannot get it into gear, the first thing you check is your speed. If you are going too fast, your best bet is put it back into the gear you were in and slow down some more. If you are going too slow, you need to step off the gas as you step on the clutch, because the engine will not need to be going as fast. That will allow it to find the gear. It will still make noise, but it will find it. When all else fails, you simply slow down to a crawl until you can stick it back in first and start over. Sure everyone in their cars behind you hates you for it, but they aren't paying as much in taxes to use the road as the bus is, so they can just deal with it!
Some buses are more forgiving than others. Some will let you goof it up a little, and they will no jerk you around as badly for it. Others are not forgiving at all, and if you mess it up, they simply will not even let you have the gear! Basically it is a lot of work and takes a lot of thinking ahead to do it. If it is stop and go traffic, you will probably break a sweat. Oh yeah, I forgot to mention that these clutches are so stiff that the only thing that keeps me from standing on them is my seatbelt. Without that, it would take most of my weight to push that pedal down! It is totally a chore, and it really makes you hate the person who darts out in front of you and then slows down. But that is how it all works. If that was not technical enough, do a little research online, and you will get it. www.howstuffworks.com is a good one.
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