Shifting
by R.J. Long A long time ago, the fellow who first allowed this green kid to drive his charter buses encouraged me to practice my shifting to be as smooth as possible. Although I'd been driving school buses, I was still rough around the edges when it came to shifting. This gentleman put shifting into this perspective: "You've got a group of people headed to the Hollywood Bowl for a black-tie performance, and they're all dressed for the occasion. Standing in the aisle talking to one of her friends is a lady wearing a beautiful white dress, and she's drinking red wine. She takes a drink just as you shift - will you ruin her evening gown?" I still think about that lady every time I put in the clutch...
Most people, especially those climbing behind the wheel for the first time, do not realize that a bus isn't shifted like a Beetle, they should be double-clutched. Proper double clutching will prolong the life of the entire power train, smooth out the shifts, and provide a more comfortable ride for your passengers. Also, if you've spent a lot of time in 18-wheelers, shifting a bus is going to drive you nuts for awhile. You've been used to 10, 13 or 15 speed gearboxes and their quick shifts and split shifts and so forth. Most buses have four or five forward speeds, so the trucking crowd has to learn to slow everything down when they shift a coach. And if the coach is not in good condition, then the process becomes a little more challenging, because it is absolutely no fun trying to stir pudding with a wet spaghetti noodle!
Ok, with those preliminaries out of the way, let's get started with those vehicles that DO NOT have a Tachometer - the GearHeads with tachs can wait awhile, but read on anyway. . .
UPSHIFTING: Everyone should be able to get their coach rolling on level ground with what is called a "Dead Throttle Start." A DTS simply means that you get the bus moving with the clutch only, keeping your right foot OFF the throttle until the clutch has been released fully. All the GMs will smoothly pull away from a dead stop at idle, even with a full passenger load, unless your coach has exceeded its designed GVW. If yours doesn't, you either need to practice your clutch technique, or you might have a clutch problem that should be checked. Try practicing DTSs in a manual transmission car first - it's easier to figure out the technique - then move back to your bus.
Before we get into upshifting, do you know the maximum road speed in each of the lower three gears? This will be the fastest road speed the bus will attain in each gear with the engine at its governed maximum. It will vary bus to bus, but most are about 15 mph in first; 30 mph in second; 45 mph in third; and fast enough for a speeding ticket in fourth. Know your bus and its particular set up, as this will be helpful later when I talk about downshifting on a hill.
Here is an interesting note about Detroits and manual gearboxes: They will tell you when to upshift by the feel of the shift lever as the engine hits the governor. Try it: get the bus moving in first using a DTS, then floor the throttle, all the while keeping your hand on the gearshift lever. If you keep a slight pull towards second on the stick, feel how the tension changes when the engine first hits the governor and then stabilizes. It's this tension change you want to use to your advantage when upshifting. If you get really good at this, you can shift up and down without the clutch, just by the feel of it, but it takes practice, and maybe some spilled wine!
First to Second upshift: Begin with DTS, bring to maximum in first gear. As soon as the tension changes on gearshift, where it's easy to pull it out of first, put in the clutch, pull the stick into neutral, let out the clutch, and count "one thousand one, one thousand two, one thousand three," and possibly, "one thousand four." As soon as your count reaches one thousand three (or four), push in clutch and gently pull gearshift towards second. If you time it right, it should just about fall in. Bring the bus to a halt, put it back into first and try again, adjusting how many "thousands" you have to count between letting the clutch out and putting it back in while the transmission is in neutral. Do not pull gearshift directly from one gear to the next without letting this "count" take place with the clutch out - serious internal transmission damage COULD occur.
Second to Third upshift: Similar to 1-2, but shorten the count by one.
Third to Fourth upshift: Similar to 2-3, but shorten the count by one more. (Two less than the 1-2 upshift.)
Now that you've practiced this idea of a "count system" to help avoid the gnashing of gears, add this little gem to work on your smoothness: Place a tapered 6 - 8 oz. Styrofoam cup filled with water on the dashboard and make your shifts without spilling the water! Be sure that where you place the water won't damage anything, especially electrical stuff, because believe me, it will spill until you figure out how to do this shifting technique correctly and smoothly. (Spills caused by potholes don't count!)
Ok, now for the GearHeads out there with tachometers, here's a little something to help you smooth out your shifts: Quit watching the tach! You're spending too much time taking your eyes off the road, and I might just be in front of you!
Seriously, learning the gear splits using a tach will help you with your shifting, especially in those situations where you're not simply upshifting or downshifting. The simple procedure is as follows:
Put bus in first gear, get rolling using a DTS, then bring the RPM up to and hold it steady at 2000. Look at the speedometer and see what the road speed is, making a note of it. Now shift to second, double-clutching properly, and hold the bus steady at the road speed that equals 2000 rpm in first gear. Once the speed's stabilized, look at the tach and note the rpm. The difference between this figure and the 2000 number is the "rpm split" for the 1-2 upshift. Now repeat this process for the 2-3 and 3-4 upshifts. You will notice that the "rpm split" is different for each of these gear changes. This is information you will need for a more professional approach to your shifting, which we'll cover shortly.
DOWNSHIFTING: There are three basic reasons for downshifting: coming to a stop; rounding a corner (or adjusting for traffic speed changes); and climbing a hill. Each is a little different, but all accomplish the same purpose - getting the bus into the right gear for the situation.
When coming to a stop, by far the laziest way is to just leave it in whatever gear until completely stopped, then shift into first. But to make things easier, try leaving it in whatever higher gear you're in as you slow until the power train just begins to "complain", then put in the clutch, pull the gearshift into neutral, let the clutch out until you're almost stopped (2-3 mph), then put the clutch back in and gently push the gearshift into first at the same time. This will take a little practice, but when you get the timing down, it will just about fall into gear. This works especially well with those coaches that have "wet clutches" in them. Some "wet clutch" buses, while still cold, will require that you shut off the engine, put the coach into first gear, then restart. Nature of the beast. . .
Besides coming to a stop, probably the most common downshifting you'll be doing is either rounding a corner or adjusting for changes in traffic flow. This becomes a piece of cake for the GearHeads with tachs after they've learned the rpm splits discussed earlier, but those without tachs can learn the technique just as well by feel - which is what the GearHeads should be doing also! The basic rhythm is as follows: clutch in, gearshift to neutral, clutch out, rev engine to proper rpm, clutch in, gearshift into lower gear slot, clutch out and you're on your way. The trick here is knowing the right engine rpm for the next gear, and this just takes lots of practice, because it changes constantly. But when you get it correct, it's smooth and sweet. In city and town driving, you'll spend a lot of time in second and third, so this is a good combination to practice shifting in both directions. For example, approach a right-hand corner in third, slow down enough to make the turn, downshift to second and accelerate away. Then go around the block and try it again. And again. Put your glass of water back on the dash and practice some more!
For the GearHeads, approach the corner, slow enough to make the turn, note the tach rpm reading, quickly add the gear rpm split to the tach reading for the next lower gear, bring the rpm to that point, downshift and accelerate. For the real technical GearHeads, that means that you add the rpm split when you downshift, and you subtract it when you upshift.
The most challenging downshifting will occur when you're climbing a hill. Get it right and you continue merrily on your way. Get it wrong, and panic can set in very, very quickly! The following suggestions should lessen the panic attacks:
Remember way back at the beginning of this article it was mentioned that you should know the maximum road speed in each of your lower gears? Now its time to use those numbers to your advantage, with the additional number five to help you through the process.
Your bus is on the highway, and a hill looms ahead. Even though you're keeping your foot on the throttle, the bus is slowing down. Start watching the speedometer. When your road speed reaches five mph above the maximum road speed in the next lower gear, downshift in the following manner: floor throttle and keep it there, clutch in and gearshift moved to neutral, clutch out, clutch back in and gearshift moved to next lower gear, clutch out and continue climbing. This all takes place very quickly, almost as fast as it took you to read it. Repeat as needed, depending on the grade. The secrets here are keeping the throttle floored, which is unusual to most people who think it will harm the engine, but Detroits rarely break when subjected to maximum governed rpm for a couple of seconds; and the timing of dropping the gearshift into the next lower gear as you're putting the clutch back in. Do it really right and the last clutch operation is almost unnecessary. This works best when you start the process five mph over the maximum speed in the next lower gear. If you drop below that point, then you have to go to the technique used for normal downshifting, but you must work faster, because gravity is working against you. This is also a type of downshift that you don't need a tachometer to do it right, just a working speedometer and knowing your bus.
As a side note, most 2-cycle Detroits (71 & 92 series) seem to pull grades best when kept between 1800 - 2000 rpm. Drop much below this range for an extended period of time and they will start overheating. When pulling within this range, watch the exhaust - if you start getting a lot of black smoke, back off the throttle slightly. If you back off the throttle slightly and the road speed starts falling away quickly, the hill's too steep for that gear and you need to downshift again.
And, as a safety tip, always come down a hill in the same gear you use to climb it. If you have a Jake brake, you can use the next higher gear, but control your speed to keep your brakes cool and maintain a good safety margin.
AUTOMATIC TRANSMISSIONS: For those of you who drive an automatic-equipped coach, here are some tips for these transmissions:
One annoying trait of automatics in a coach, especially V-730s, is a constant "hunting" between gears when driving around town. Avoid this by simply selecting the lower gear and leaving it there. Your passengers will appreciate the smoother ride, and it will not do any harm.
If the coach has ATEC transmission controls, it is much smoother to let the electronics handle the upshifts, but this isn't necessarily true for the HT series units. Although the first upshift cannot be controlled manually, doing so in the other gears can smooth out the ride even more.
Most of the time when you're driving an automatic and you start pulling a hill, the transmission will downshift on its own. The problem is that frequently it is too late, and the next lower gear is already too high, so another downshift is just seconds away. Either that, or the downshift has been delayed so long that now the engine is starting to overheat, especially with the two-stroke Detroits. Avoiding this problem just requires a little attention and memory.
Like the manual folk, find out what the maximum road speed is that the coach will achieve in each of the lower gears. Now, when you are pulling a grade, and just before you reach the maximum road speed for the next lower gear, (approximately 2-3 mph over), come off the throttle slightly - just enough to take the load off the power train. As soon as the drive load is released, come back onto the throttle and downshift at the same time. If you time it correctly, the downshift will be smooth. It takes practice, and each Allison shifts a little differently, but it can be done.
Into the Sunset:
Ok, it's time. . . Get up, get away from the computer, or the easy chair, or the TV, fire up that big old diesel, and head for a quiet traffic area where you can make mistakes and not get into trouble. An industrial park or a high school or college parking lot on the weekends is a great place to work out, so go do it! Spend a couple hours on DTSs, the 1-2 upshift, 3-2 downshifts, downshifting around a corner, etc., and soon you'll start feeling much more confident about piloting these mighty coaches down the highway.
See you down the road. . .
"Shifting a Manual Gearbox Coach" © 2001 BTW Musings, Ltd. - R. J. Long. Internet © BNO. All Rights Reserved. Reproduced with permission of the author.
