From: SMTP%"HONDA-L@BROWNVM.BROWN.EDU" 12-AUG-1996 23:06:15.17 Subj: HONDA-L Digest - 6 Aug 1996 to 12 Aug 1996 ------------------------------ Date: Mon, 12 Aug 1996 22:39:59 -0400 From: Fei Chen Subject: a compilation of responses hi all, i want to thank all who responed to my questions. i compiled the answers and hope that it might prove useful. (i'm quoting people's reponses below, credit is given wherever it's due.) Q: clutch or not clutch? A: 1) Its usually best to only keep the clutch-pedal depressed for the shortest period possible.If you leave the clutch in, you will prematurely wear the clutch pivot bearing. so when you're waiting at a light, put the car in neutral and take your foot off the clutch. Hold the car with your brake, or the emergency brake. The people you see rollng their car back and forth at stoplights are usually the ones who replace their clutch every year. to minimize clutch wear when downshift, using the double clutch, rev-matching technique: 1. put clutch in and gear into neutral 2. let clutch out 3. as you blip the throttle to get the rpm's up to match the lower gear, put clutch in and downshift 4. let the clutch out Double clutching does 2 things. It makes your downshifts much smoother and it allows your gear synchros to relax. You synchronize the gear and drive axle by rev-matching. However, if you only rev-match and don't double clutch, you still wear the synchro's since they are "spinning" too slow. The synchro's are set for the higher gear and when you double clutch, you free the synchros to spin at whatever they want. Double clutching won't wear the pivot bearing as long as you don't keep the clutch engaged. Engage clutch, neutral - do this quickly so that your leg doesn't stop moving. What wears the bearing is if you stop in the middle of using the clutch. As far as upshifting, you should rev-match here again but no need for double clutching. Just let the engine rpms drop to match the bigger gear at the speed you're going in. ------------------------------------------------------------------------------ the following is due to David Lane: Double clutching is really only useful for truck transmissions, which don't have synchromesh gearboxes, and is generally only used when downshifting. I am not an expert on this, and it is complicated to explain without drawings or a working model, but I can probably give you a mostly accurate description of how it works. In theory, the transmission transmits power from the engine to the car's wheels and tires--we will call them the road wheels for short. In the simplest terms, the road wheels are connected to a single gear in the transmission. There are five gears of different sizes attached to the engine. Each time you upshift, a smaller diameter gear from the engine is meshed with the road wheel gear. Now, since the road wheel gear can only turn at one rate of speed (depending on how fast you are going) the engine speed must change to accommodate the different gear ratios in the transmission. This is not unlike riding a multi-speed bike. If you go at 10 mph and switch gears, your legs will change speed while your road speed stays the same. It would be damn difficult to change gears if the engine were always connected to the transmission. Fortunately, when you depress the clutch, the engine is disconnected from its gears. When you push the shifter to the next gear, there are "synchromesh rings" in front of the gear which matches the speed of the engine-driven gears to the speed of the road wheel gear--speeding the engine-driven gears up, or slowing them down as necessary. Once the synchromesh gets the two gears going at the same speed, the teeth will mesh and the shift is accomplished. Without synchromesh, if the two gears are not going at the same speed, the gear teeth will grind against each other, which is not good for the transmission. You have no synchromesh in reverse, which is why you have to be stopped to shift there. If you are rolling forward, the road wheel gear will be moving, and you will hear a grind. Anyway, double clutching is a way to match the engine speed in a given gear to the road wheel speed, in a transmission without synchromesh. In a downshift, you depress the clutch and come into neutral. The engine needs to be going at higher rpms to accommodate the speed of the road wheel gear, so you let the clutch out (still in neutral)--which re-attaches the engine driven gears to the engine. Then you blip the throttle to increase the engine speed, which gets the engine-driven gears spinning faster, until they are going at the right speed to mesh with the road wheel gear. You push the clutch back in, and if you have done it right, the shifter will move easily into the lower gear. If you miss, you will hear a lot of grinding and probably a lot of cursing will come from your lips. Oh, well. That's why they have truck driver's school. Let the clutch out, and you are on your way. As you can see, synchromesh makes the whole process much easier. When downshifting, you can hold the clutch in just once and blip the throttle, which will do some of the work for the synchromesh and make the mechanical parts last longer. If you are not exactly on target, the synchros will do the rest of the work for you. Now you can see why upshifting does not require any fancy clutch work. When you upshift, the engine slows down between gears. It will do this anyway as soon as you take your foot off the accelerator and depress the clutch. If you pause for a moment in neutral, it will give the engine a chance to slow down enough to align the gears, and the stick will easily slip into the next higher gear. If you are in a race, push harder on the stick and go directly from gear to gear. The synchros will match speeds for you. In the broadest view, all we are talking about is smooth driving and saving some wear and tear on the synchromesh. There are a lot of old ladies out there who have never heard of any of this, and who's transmissions last a good long time. Performance drivers are much more likely to stress their cars, so they tend to find ways to make less work for the transmission if possible. Here is an experiment for you. Go out on a road where you have some room. Put the car in third and go at about 3000 rpm. Maintain speed and see how fast the engine is going when you shift to forth. let's say it is about 2200 rpm. Now go back into third at 3000 and put a little pressure (one or two fingers) on the shifter toward neutral. Don't depress the clutch. Nudge the accelerator a little to remove the tension between gears, and the the stick will move out of gear, into neutral. Take your foot off the accelerator, and put a little pressure on the stick toward forth gear. When the engine rpm drops to 2200 rpm, the stick will probably slide into forth without you ever pressing on the clutch. If you miss, and the engine rpm drops below 2200, just give it a very little gas to get it back to that speed. When the engine speed matches the road wheel speed, it should drop into gear. That should illustrate how it works. Be real gentle with the shift lever, and you won't hurt anything. Push too hard, and you will hear a grind. It is more difficult doing this trick going from forth to third, but all you have to do is use the accelerator to raise the engine speed while in neutral. Very few drivers know how to shift without the clutch, and I offer this description to you for your amusement and experimentation. Obviously I won't be responsible if you break something--although if you stay gentle with the shifter, the worst you may experience is a little, soft grinding sound. If you hear that, go back to neutral and either try again, or give up. I had to learn this trick when I blew my clutch at an autocross, thirty miles away from home. It was my own fault, I lost track of how fast I was going and tried to downshift into first, which over-reved the engine and disintegrated the clutch friction surface. I actually drove the car home, matching gears, without ever using the clutch. I had to go real slow near stop lights, and once or twice I had to stop the car and start it in first gear to get going again. That was in the days before cars had to have the clutch pedal pressed in order to start them. David Lane dlane@peabody.jhu.edu --------------------------------------------------------------------------- some more tips on the clutch: You'll get smoother starts if you give the car a little gas and then slowly let up on the clutch. Also, NEVER hold the car on a hill by holding the clutch in halfway. This puts trmendous wear on the clutch. Every car's clutch is a little different, so experiment and see what works. Also, peeling out (popping the clutch with a lot of gas) can cause damage to the clutch. If you are holding the car on a hill, use the brakes. Believe it or not, some people try to do it by slipping the clutch and reving the engine. All that gets you is unnecessary wear. One trick to starting out on a hill without drifting backward too far is to use the hand brake. Engage the hand brake, put the car in first and let the clutch out until it just starts to engage. The engine will start to slow a little. Immediately release the hand brake and you will be under way without any drifting. Pause as you pass through neutral when upshifting. This will give the engine a chance to slow down and match speeds with the higher gear. If you rush the process, the transmission's synchromesh rings will do the matching for you, but they will last longer if you don't rely on them so much. This is also why it is helpful to blip the throttle when downshifting. It also makes for a smoother ride for your passengers. As far as making the car last a long time, the best thing you can do is to change oil and oil filter every 3,000 miles and be sure to use a good quality oil of the weight recommended by Honda. Keep your tires inflated about 2-3 PSI higher than what is stated on the door; this will make them wear better and run cooler. Have your brakes checked and also 4-wheel alignment checked every 20,000 miles; in between checks, rotate your tires as per the manual every 5,000 miles. Q: first or not first? A: 2) First is such a short gear, in most cars its really only used to get the car rolling, and 2nd and up is where you pick up some actual speed. Many people just leave the car in whatever gear its in and use the brakes, not downshifting at all. Some pop the car into neutral and coast and just use the brakes to stop. Some downshift. Its all up to you, but usually there's no need to go all teh way to 1st when downshifting....usually you're going so slow at that point a downshift to first would be useless. Q: rpm? A: 3) The idea is to keep the engine comfortable--somewhere between the shaking you mentioned from lugging it (too low rpm) and unnecessary reving, which wastes gas and does cause a little additional wear. Use your ear and common sense. 2000rpm is a great place to be if you are in first gear and anticipate the need to accelerate quickly. It is also just fine for holding a steady speed in 4th or 5th gear, providing you only want to maintain your speed. have your clutch adjusted occasionally (follow Honda's reccommedned schedule) your transmission/shift. Honda engines are very flexible, and as long as you are not over the redline, or at such low rpm that the engine is obviously not smooth, you can select lower gears for performance, or higher gears for cruising. one more question i have: i live in an area where it's very hilly, thus i use the clutch a lot. my question is, is it a good practice to disengage the clutch (while still in gear) to slow down the car? i do this a lot, and i wonder if it's good. thanks again for all the responses. fei ------------------------------ End of HONDA-L Digest - 6 Aug 1996 to 12 Aug 1996 *************************************************