Manual Transmssion Questions...
11-17-1999, 03:44 PM
#1
Guest
Posts: n/a
Manual Transmssion Questions...
Having driven manual transmission vehicles of all sorts for nearly 15 years, I thought I knew everything there was to know about how to properly operate a manual transmission, however, I do not really understand in detail exactly how a manual transmission works. I've recently been trying to teach myself how to heel-toe shift, and after doing a lot of research in the forum archives regarding both heel-toe shifting and double-clutching, I have a few questions that I am hoping I can get some help with:
1. When stopped, does holding the clutch in all the way to the floor with the transmission in first gear result in increased wear relative to leaving the transmission in neutral and letting the clutch all the way out? How and why?
2. When in neutral and stopped, does holding the clutch in all the way to the floor result in increased wear relative to having the clutch all the way out? How and why? What about when the car is in neutral but moving?
3. I understand that double clutching is not absolutely necessary with a synchronized gear box, but that it can reduce wear on the synhcros in particular. How much wear does double clutching really eliminate, and are there any other benefits to double clutching? How and why?
4. Does double clutching provide benefits only for down shifting, or are there up shifting benefits as well? Again, please provide details.
5. How much additional wear does single clutch heel-toe shifting/matching revs create versus double clutching heel-toe shifting/matching revs? Again, how and why?
6. How does one go about determining the optimal shift points for a given car? Again, the more detail, the better.
That's probably enough for one post. Thanks in advance for your answers, or perhaps someone can recommend a good reference book for me. I feel like I should already know all this stuff, but I'm afraid I do not even know enough to be dangerous.
1. When stopped, does holding the clutch in all the way to the floor with the transmission in first gear result in increased wear relative to leaving the transmission in neutral and letting the clutch all the way out? How and why?
2. When in neutral and stopped, does holding the clutch in all the way to the floor result in increased wear relative to having the clutch all the way out? How and why? What about when the car is in neutral but moving?
3. I understand that double clutching is not absolutely necessary with a synchronized gear box, but that it can reduce wear on the synhcros in particular. How much wear does double clutching really eliminate, and are there any other benefits to double clutching? How and why?
4. Does double clutching provide benefits only for down shifting, or are there up shifting benefits as well? Again, please provide details.
5. How much additional wear does single clutch heel-toe shifting/matching revs create versus double clutching heel-toe shifting/matching revs? Again, how and why?
6. How does one go about determining the optimal shift points for a given car? Again, the more detail, the better.
That's probably enough for one post. Thanks in advance for your answers, or perhaps someone can recommend a good reference book for me. I feel like I should already know all this stuff, but I'm afraid I do not even know enough to be dangerous.
11-17-1999, 05:43 PM
#3
Guest
Posts: n/a
Re: My own questions
Here's the skinnies from an "almost" old-timer.. Double clutching was when there were NO syncros..Upshifts ..clutch in ..shift to neutral goose the throttle to bring the planetary gear speed up near the gear speed "to be" selected..drop in that next higher gear and so on. Do it same to down shift..its easier to do than explain. Heel/toe heel on the gas toe on the brake when you were manuel shifting without syncros and in a race..brake/shift/throttle on , etc...clutching too!! REAL MEN !!
11-17-1999, 06:38 PM
#4
Guest
Posts: n/a
I'm not a gear head, but I play one on TV (long)...
Disclaimer: I've never taken a course, couldn't put together a tranny if I tried, and have read a little on the subject. But, in 17 years, I've never had a gear box problem. And my 87.5 Coupe GT is at 207,000 and still on the original clutch...thank you very much.
What follows, is what I've learned from watching my older brothers rebuild a multitude of American muscle cars and mostly British touring cars, and conversations with friends who have plenty of track time. So, I hope this is close, but wouldn't be surprized that some of it is off the mark...
1. When stopped, does holding the clutch in all the way to the floor with the transmission in first gear result in increased wear relative to leaving the transmission in neutral and letting the clutch all the way out? How and why?
If the clutch is engaged, the gears are not, so no wear. If you leave it out an in nuetral, the throw out bearing is getting wear, however very minimal. But, now the gears are spinning with the RPM's of the engine, so reengaging the clutch will allow you to get back in gear, but you can shift too early and start to wear the syncro's, or worse grind gears.
My suggestion leave it in gear, and engage the clutch while stopped. This is also one of the reasons why Audi forces you to engage the S4 clutch before starting.
2. When in neutral and stopped, does holding the clutch in all the way to the floor result in increased wear relative to having the clutch all the way out? How and why? What about when the car is in neutral but moving?
No, that's what it is intended to do. Also this is a hydrolic clutch (with self adjustments) which makes this a very durable set-up.
3. I understand that double clutching is not absolutely necessary with a synchronized gear box, but that it can reduce wear on the synhcros in particular. How much wear does double clutching really eliminate, and are there any other benefits to double clutching? How and why?
The biggest advantage to double clutching, is rev matching. When you match engine speed and tranny speed there is less (or no) wear on the syncro's. As you down shift, your revs will increase, by blipping the throtle, you bring the tranny revs up to the engine, this way your shifts are faster and you have more power coming out of the corners (where races are won).
4. Does double clutching provide benefits only for down shifting, or are there up shifting benefits as well? Again, please provide details.
I guess there is the rev matching thing, but not as noticable. More importantly, don't force your up shifts (bang gears) that is where most tranny damage is done. My guess is that all the stop light S4 racers out there are putting a lot of pressure on 2nd gear. 1st is short, and the throw to 2nd is long, so if you want to get into 2nd fast, you are putting pressure on that syncro.
5. How much additional wear does single clutch heel-toe shifting/matching revs create versus double clutching heel-toe shifting/matching revs? Again, how and why?
Ahh...I'm not sure of your question. Heel-toe is a (very dificult manuver, IMHO to master)technique for appling the brakes while blipping the throtle (needed to rev match while double clutching). I'm not sure what you mean by,"single clutch heel-toe shifting/matching revs".
6. How does one go about determining the optimal shift points for a given car? Again, the more detail, the better.
Depends on the driving situation, and power band requirements. For flat out speed, you want to shift at the top of the power band. However, as you're heading into a corner in say second, you might want to hold second, scrub off some power, and hit it again in the corner, upshifting as you exit.
Hope this helps (and is close)...
What follows, is what I've learned from watching my older brothers rebuild a multitude of American muscle cars and mostly British touring cars, and conversations with friends who have plenty of track time. So, I hope this is close, but wouldn't be surprized that some of it is off the mark...
1. When stopped, does holding the clutch in all the way to the floor with the transmission in first gear result in increased wear relative to leaving the transmission in neutral and letting the clutch all the way out? How and why?
If the clutch is engaged, the gears are not, so no wear. If you leave it out an in nuetral, the throw out bearing is getting wear, however very minimal. But, now the gears are spinning with the RPM's of the engine, so reengaging the clutch will allow you to get back in gear, but you can shift too early and start to wear the syncro's, or worse grind gears.
My suggestion leave it in gear, and engage the clutch while stopped. This is also one of the reasons why Audi forces you to engage the S4 clutch before starting.
2. When in neutral and stopped, does holding the clutch in all the way to the floor result in increased wear relative to having the clutch all the way out? How and why? What about when the car is in neutral but moving?
No, that's what it is intended to do. Also this is a hydrolic clutch (with self adjustments) which makes this a very durable set-up.
3. I understand that double clutching is not absolutely necessary with a synchronized gear box, but that it can reduce wear on the synhcros in particular. How much wear does double clutching really eliminate, and are there any other benefits to double clutching? How and why?
The biggest advantage to double clutching, is rev matching. When you match engine speed and tranny speed there is less (or no) wear on the syncro's. As you down shift, your revs will increase, by blipping the throtle, you bring the tranny revs up to the engine, this way your shifts are faster and you have more power coming out of the corners (where races are won).
4. Does double clutching provide benefits only for down shifting, or are there up shifting benefits as well? Again, please provide details.
I guess there is the rev matching thing, but not as noticable. More importantly, don't force your up shifts (bang gears) that is where most tranny damage is done. My guess is that all the stop light S4 racers out there are putting a lot of pressure on 2nd gear. 1st is short, and the throw to 2nd is long, so if you want to get into 2nd fast, you are putting pressure on that syncro.
5. How much additional wear does single clutch heel-toe shifting/matching revs create versus double clutching heel-toe shifting/matching revs? Again, how and why?
Ahh...I'm not sure of your question. Heel-toe is a (very dificult manuver, IMHO to master)technique for appling the brakes while blipping the throtle (needed to rev match while double clutching). I'm not sure what you mean by,"single clutch heel-toe shifting/matching revs".
6. How does one go about determining the optimal shift points for a given car? Again, the more detail, the better.
Depends on the driving situation, and power band requirements. For flat out speed, you want to shift at the top of the power band. However, as you're heading into a corner in say second, you might want to hold second, scrub off some power, and hit it again in the corner, upshifting as you exit.
Hope this helps (and is close)...
11-17-1999, 07:42 PM
#5
Guest
Posts: n/a
Re: I'm not a gear head, but I play one on TV (long)...
Left this alone on purpose but can't let anyone get wrong info
#1 Holding the clutch in at a stop increases wear on the throw out bearing because it is pushing in the presure plate, the reason Audi has you push in the clutch is because there have been boneheads starting cars in gear and causing injury or damage to what ever is in the way.
#2 see #1
Don't even want to touch the others.
#1 Holding the clutch in at a stop increases wear on the throw out bearing because it is pushing in the presure plate, the reason Audi has you push in the clutch is because there have been boneheads starting cars in gear and causing injury or damage to what ever is in the way.
#2 see #1
Don't even want to touch the others.
Trending Topics
11-18-1999, 07:01 AM
#8
Guest
Posts: n/a
Re: Manual Transmssion Questions...
1. When stopped, does holding the clutch in all the way to the floor with the transmission in first gear result in increased wear relative to leaving the transmission in neutral and letting the clutch all the way out? How and why?
There is wear on the clutch release (throw out) bearing if you hold in the clutch. I believe this is a roller bearing these days, not the graphite ones that used to be used (and caused that terrible shrieking noise when worn out), and is pretty durable, so I wouldnt worry about it.
2. When in neutral and stopped, does holding the clutch in all the way to the floor result in increased wear relative to having the clutch all the way out? How and why? What about when the car is in neutral but moving?
Well holding the clutch in stops the gears in the gearbox turning, but causes wear on the clutch release bearing (see 1).
3. I understand that double clutching is not absolutely necessary with a synchronized gear box, but that it can reduce wear on the synhcros in particular. How much wear does double clutching really eliminate, and are there any other benefits to double clutching? How and why?
Double declutching is essential on non syncro gearboxes (think 1950s) and is of benefit to older syncro gearboxes, particularly ones in powerfull hi torque cars like the american lead sleds of the 60s-70s. If you watch movies like Bullit or Vanishing point you can hear the cars being double declutched. Modern boxes with double or triple syncros dont need this technique.
Heel and toe braking is still a usefull if difficult technique, but only if you are doing a hard brake and then need to be in the right gear immediately for pulling away ie racing cornering.
One feature of our modern sanitized fuel injected OBDII compliant world is that throttle off rev decay in engines takes a lot longer, so for non furious slowing down the need for heel and toe is much reduced.
4. Does double clutching provide benefits only for down shifting, or are there up shifting benefits as well? Again, please provide details.
Not much benefit to either anymore.
5. How much additional wear does single clutch heel-toe shifting/matching revs create versus double clutching heel-toe shifting/matching revs? Again, how and why?
There is extra wear on the gearbox synchros, but modern gearboxes are built to handle this.
6. How does one go about determining the optimal shift points for a given car? Again, the more detail, the better.
I assume you mean for maximum acceleration. Trial and error is the only way. The optimal shift point for turbo cars is not necessarily maximum revs.
There is wear on the clutch release (throw out) bearing if you hold in the clutch. I believe this is a roller bearing these days, not the graphite ones that used to be used (and caused that terrible shrieking noise when worn out), and is pretty durable, so I wouldnt worry about it.
2. When in neutral and stopped, does holding the clutch in all the way to the floor result in increased wear relative to having the clutch all the way out? How and why? What about when the car is in neutral but moving?
Well holding the clutch in stops the gears in the gearbox turning, but causes wear on the clutch release bearing (see 1).
3. I understand that double clutching is not absolutely necessary with a synchronized gear box, but that it can reduce wear on the synhcros in particular. How much wear does double clutching really eliminate, and are there any other benefits to double clutching? How and why?
Double declutching is essential on non syncro gearboxes (think 1950s) and is of benefit to older syncro gearboxes, particularly ones in powerfull hi torque cars like the american lead sleds of the 60s-70s. If you watch movies like Bullit or Vanishing point you can hear the cars being double declutched. Modern boxes with double or triple syncros dont need this technique.
Heel and toe braking is still a usefull if difficult technique, but only if you are doing a hard brake and then need to be in the right gear immediately for pulling away ie racing cornering.
One feature of our modern sanitized fuel injected OBDII compliant world is that throttle off rev decay in engines takes a lot longer, so for non furious slowing down the need for heel and toe is much reduced.
4. Does double clutching provide benefits only for down shifting, or are there up shifting benefits as well? Again, please provide details.
Not much benefit to either anymore.
5. How much additional wear does single clutch heel-toe shifting/matching revs create versus double clutching heel-toe shifting/matching revs? Again, how and why?
There is extra wear on the gearbox synchros, but modern gearboxes are built to handle this.
6. How does one go about determining the optimal shift points for a given car? Again, the more detail, the better.
I assume you mean for maximum acceleration. Trial and error is the only way. The optimal shift point for turbo cars is not necessarily maximum revs.
11-18-1999, 07:41 AM
#9
Guest
Posts: n/a
Clarification: Single Clutch Heel-Toe VS. Double Clutch Heel-Toe
By single clutch heel-toe shifting I basically just mean heel-toeing to match revs on the downshift to avoid unsettling the car when cornering for example. The process would go something like the following for a single clutch heel-toe downshift:
1. Right foot on brake, push in the clutch pedal.
2. While still braking with clutch pedal in, downshift gear box while "blipping" the throttle via heel-toe with the right foot to match revs for the lower gear.
3. Release the clutch pedal to complete the downshift.
In contrast a double clutch heel-toe downshift would be a little more complicated and time consuming:
1. Right foot on brake, push in the clutch pedal.
2. While still braking with clutch pedal in, shift gear box to neutral and release clutch pedal.
3. While still braking with clutch pedal released, "Blip" the throttle via heel-toe with the right foot to match revs for the lower gear.
4. While still braking and holding appropriate revs for the lower gear via heel-toe as necessary, push the clutch pedal back in and shift gear box to the lower gear.
5. Release the clutch pedal to complete the downshift.
I believe that the functional difference between the two is only that using the double clutch saves wear and tear on the transmission synchros, but is more difficult and takes longer. The questions is how much wear, and are there any other benefits to the double clutch heel-toe downshift.
A corollary question for double clutch heel-toe downshifting might also be whether or not one can skip, chew gum, whistle a merry tune, pat oneself on the head, and rub one's stomach in a circular motion all at the same time, but I digress...
1. Right foot on brake, push in the clutch pedal.
2. While still braking with clutch pedal in, downshift gear box while "blipping" the throttle via heel-toe with the right foot to match revs for the lower gear.
3. Release the clutch pedal to complete the downshift.
In contrast a double clutch heel-toe downshift would be a little more complicated and time consuming:
1. Right foot on brake, push in the clutch pedal.
2. While still braking with clutch pedal in, shift gear box to neutral and release clutch pedal.
3. While still braking with clutch pedal released, "Blip" the throttle via heel-toe with the right foot to match revs for the lower gear.
4. While still braking and holding appropriate revs for the lower gear via heel-toe as necessary, push the clutch pedal back in and shift gear box to the lower gear.
5. Release the clutch pedal to complete the downshift.
I believe that the functional difference between the two is only that using the double clutch saves wear and tear on the transmission synchros, but is more difficult and takes longer. The questions is how much wear, and are there any other benefits to the double clutch heel-toe downshift.
A corollary question for double clutch heel-toe downshifting might also be whether or not one can skip, chew gum, whistle a merry tune, pat oneself on the head, and rub one's stomach in a circular motion all at the same time, but I digress...
11-18-1999, 12:26 PM
#10
Guest
Posts: n/a
Shift points
Essentially, you don't want to shift unless you're going to accelerate faster in the next gear than you would accelerate leaving it in the current gear. To calculate these, you must know what the torque curve of your engine is (meaning=detailed dyno output) and what the gear ratios are relative to each other. I've calculated shift points after seeing two dyno curves for S4's posted -- APR's graph and MTM's euro-spec graph. In stock configuration, I believe I calculated the shift points as follows:
1-2: 7000 (both)
2-3: 7000 (APR); 6800 (MTM)
3-4: 6800 (APR); 6400 (MTM)
4-5: 6600 (APR); 6300 (MTM)
5-6: 6500 (APR); 6200 (MTM)
The MTM dyno graph showed more peak torque and actually less torque near the redline than APR's dyno graph showed, so this is why there are differences. After either maker's chip is installed, the shift points get a few 100 RPM lower because peak torque gets much higher and near the redline torque goes up not quite so much. Note that if there is a great disparity in gear ratios, usually the optimum shift points will nearly always be accomplished at the redline unless the engine has a monstrous amount of torque available lower in the power band than it does at high RPMs (1st-2nd shift for example where the gear ratios are 3.5 vs. 1.889).
1-2: 7000 (both)
2-3: 7000 (APR); 6800 (MTM)
3-4: 6800 (APR); 6400 (MTM)
4-5: 6600 (APR); 6300 (MTM)
5-6: 6500 (APR); 6200 (MTM)
The MTM dyno graph showed more peak torque and actually less torque near the redline than APR's dyno graph showed, so this is why there are differences. After either maker's chip is installed, the shift points get a few 100 RPM lower because peak torque gets much higher and near the redline torque goes up not quite so much. Note that if there is a great disparity in gear ratios, usually the optimum shift points will nearly always be accomplished at the redline unless the engine has a monstrous amount of torque available lower in the power band than it does at high RPMs (1st-2nd shift for example where the gear ratios are 3.5 vs. 1.889).