Double Clutch Your Straight Drive Mustang
| 31 March 2009
[ If you routinely read the monthly automotive magazines, you’ve no doubt seen reference to double clutch transmissions, more recently called dual clutch transmissions. A double clutch transmission is a design feature, not to be confused with double clutching which is a driving technique. (ds) ]
In the February Pony Tricks, I left you hanging when I mentioned the straight drive shifting technique called double clutching. I didn’t go into the details of how it’s done but said I’d get back to it somewhere down the road. So why not this month, while it’s still fresh in my mind?
In February’s column, I was talking about driving smoothly when shifting from gear to gear. Double clutching came into the picture as a technique for smoothing out downshifts. Several examples of when you might want to double clutch could include going into a lower gear in preparation for passing on a 2-lane road; shifting to a lower gear when climbing a steep grade; needing a lower gear on sharp corners such as switchbacks; or simply selecting a lower gear when turning at an intersection or entering your driveway.
If you’ve ever tried to shift your late model Mustang into first gear at 10 mph, the last example could make you a believer in the convenience of double clutching . Even though the gear is synchronized, it’s pretty difficult to downshift into it smoothly at that speed, or at all for that matter, unless you double clutch.
I learned to double clutch in the 1950s when many of the cars and light trucks of the late 40s and early 50s were difficult to downshift if the vehicle was moving. In those days, most of the passenger cars had three speed transmissions with a column shifter while the light trucks had three speed or four speed transmissions, usually with a floor shifter. First gear and reverse weren’t synchronized but the other gears all had synchronizers, such as they were. The synchronizers worked well enough on upshifts but the same couldn’t be said for downshifts. Out of self preservation, you needed a good grasp of double clutching to handle the cantankerous nature of the synchronizers when shifting to a lower gear. It was either that or spend your time grinding gears or missing shifts, all the while enlarging your vocabulary of blue words.
I have a cousin who lives along the Delaware River in Port Jervis, NY, just a stone’s throw north of the New Jersey state line. In the late 1950s she worked in upstate Jersey and her drive to work took her through High Point State Park, New Jersey’s highest elevation. The road to High Point was steep. Over the short distance of about three and a half miles, the elevation changed 1400 feet from the river bank in Port Jervis to the top of the mountain. Her only transportation was a well used 1948 Chevy coupe with the 90 hp 216 cid straight 6 and a three speed on the column. The car couldn’t climb the steep road in third gear. It made it ok in second but she couldn’t downshift the well worn transmission into second gear while she was moving. One of her friends thought she needed to double clutch to make the shift but neither one of them knew what that meant. So her solution was to stop part way up the hill, start again in first gear, and then upshift to second.
She found out that I knew how to double clutch so the next time our family was visiting her family, she asked me to teach her. We started on the level street in front of her house. She got the idea in slow motion and with practice, she got pretty good as long as we were on a fairly level road where the car coasted easily. But on the hill where the car slowed quickly, she couldn’t complete the shift before the car was going too slow for second gear to work. As long as she worked in New Jersey, she had to stop part way up the hill, start over again in first gear, and upshift to second to finish the climb.
The only reason I mentioned her experience was to point out that double clutching is a learned technique but to do it, you have to be committed, focused, and confident. Although she was confident on level roads, my cousin never developed confidence on the hill, where it mattered.
Double clutching is a mindset. It’s easy to do but at first it’s counter-intuitive. You have to issue your mind a clean sheet of paper and set about perfecting the moves. So let’s get down to the details of what’s going on when you double clutch and then go through the steps of how to do it.
When you double clutch , you’re matching the engine speed and the transmission gear speed to the requirements of the drivetrain in the lower gear. Let’s say you’re driving your Mustang on a 2-lane road in 5th gear behind a car that’s puttering along at 50 mph. You’d like to pass and finally you see a stretch of road approaching where you can do so safely. The passing zone is relatively short but no problem if the transmission is in a lower gear so that you can accelerate quickly. Third gear seems about right so just before you’re ready to pass, you double clutch smoothly into third. Your car maintains it’s road speed and the new gear is selected without any lurching or jerking. When you enter the passing zone, you punch the accelerator and complete your pass, upshifting as you go.
Let’s break it down. What did you do going into third gear? First you depressed the clutch pedal and then you shifted to neutral where you paused briefly. While you were in neutral, you released the clutch pedal and quickly stabbed and released the accelerator to bring the engine speed and the transmission gear speed to an rpm somewhat higher than the rpm you would need for third gear at 50 mph. The next moves were to depress the clutch pedal again, select third gear, catch the engine speed as it slowed to the rpm needed, and engage the clutch. All of this was executed very quickly in what appeared to be one fluid move, except there was actually that pause for a fraction of a second in neutral. In all, it took about one second to make the shift and you did it just before you were ready to pass.
How do you learn to make the moves and develop the timing necessary to double clutch without missing a shift and possibly damaging your transmission? Before you start, find a safe place to practice. A straight and level section of a lightly traveled back road might be a good place. Drive along at about 45 mph in fifth gear and double clutch into third by deliberately going through each of the individual steps I mentioned above. Don’t be concerned if it takes three or four seconds or more to complete the steps. At this point your learning the mechanics of the technique. Don’t try to make it look like one fluid move at the outset. Here are the steps again: 1.)depress the clutch pedal, 2.) shift to neutral, 3.) release the clutch pedal, 4.) quickly stab and release the accelerator taking the rpm somewhat higher than you’ll need to maintain your road speed for the gear you’re shifting into, 5.) depress the clutch pedal again, 6.) shift to the new gear, and 7.) catch the engine speed with the accelerator as you 8.) release the clutch pedal to engage the gear. Catching the engine speed means you’re back on the accelerator as the engine slows from the stab and release. You’re “catching” its speed at the rpm needed for the gear you selected, third gear in this example.
When the sequence of moves begins to feel comfortable, you should go to the next step where you practice smoothing out the process by working on your overall timing. Your confidence will build as you practice and soon the entire shift will take very little time. Now your on your way. With more practice you’ll soon be down in the range of one second. When you get to that point, go through the entire learning process again only this time practice shifting from fifth to second until you again find yourself in the range of one second to complete the shift. You should be feeling pretty good about the technique by now so it’s time to apply double clutching to your every day driving experience. As you use it more and more, your timing will continue to improve and the entire process will become automatic.
Here’s a precaution: Don’t let too much theory muddy the waters. You might read an article about double clutching where the author gives an example of what the engine speed will be in the gear you’re leaving vs. the rpm you’ll need for the gear you’re selecting and then suggests that you specifically aim for the new rpm. It’s all true if you want to talk about theory but double clutching happens so fast, it’s not possible to read the tachometer during the process. Besides, for each road speed and gear selection, there’s a different rpm relationship, meaning you would need to make calculations in a flash and then apply them on the fly. It’s just not possible to go through that process in real time.
Using my Cobra as a guinea pig, the engine is theoretically turning 1434 rpm in fifth gear at 50 mph. If I wanted to use third gear to pass like in the earlier example, I’d double clutch into third where 50 mph would require 2848 rpm. The engine would be turning at the new rpm just prior to starting the pass. If I wanted more punch, I could use second gear where the rpm at 50 mph would be 4261. But in real life, don’t expect me to make the calculation or to look at the tach when I shift. I’ll be too focused on driving the car.
So how do you get the right rpm for the gear you’re selecting? Right out of the box you’ll recognize that the accelerator needs more of a stab if you’re going to second gear and less of a stab going to third. Getting it right and catching the rpm at the right engine speed is an acquired feeling that develops over time. There’s a place for theory but the acquired feeling is what you’ll depend on in real life. Just don’t downshift to a gear that pushes the rpm close to the engine’s red line, or possibly beyond it.
On a final note, I recall reading an article about double clutching where the catch phrase was, “It’s easier to do than to explain.” I’d certainly agree with that statement but it will never be easy unless you say to yourself, “I really want to do this.” If you make that commitment, then you can focus on the task, learn the process, and gain the confidence. It boils down to how connected you want to be with your car and the driving experience. If you really don’t want to learn the technique or if you try it for a period of time without developing a high level of confidence, then it’s best to forget about it. I’m sure my cousin would enjoy the company. Other than more wear and tear on the drivetrain, there’s nothing wrong with downshifting without double clutching.
By the way, I forgot to mention that when I drove the old 48 Chevy up the hill to High Point, I was able to easily downshift to second by double clutching. I think I was called a showoff or a smart@#$ or some such characterization. Que sera, sera.