downshifting
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downshifting
i am just curious .... it says on the manual about the first 1000 mile. they tell you do not attempt to stop the car by shifting down gears, and so wat's the possible problem it might lead to if people really did it.
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From: Texas
2004 SLK Special Edition
I think they are concerned that if you are not careful when downshifting you will cause the engine to rev really high, or redline when the car is new. I don't think this would be a good thing to do ever so just be careful. Also when I had just gotten my coupe, I used to slow down alot by downshifting, if you get in the habit of doing this just remember that you're putting wear and tear on your clutch and syncros just so you can slow down whereas you could be wearing down something much less valuable being your brakepads. Sorry I went off on a tangent but we discussed this topic a while back on the forum. Enjo your new car and break it in properly. Some people will tell you not to worry about breaking it in but it's a good idea and will help determine how well your car performs in the future. It's important to vary your engine speed when driving on the highway and not keep the car at a certian RPM for an extended period of time.
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
rétrogradage
Originally posted by adamrs80
...I used to slow down alot by downshifting, if you get in the habit of doing this just remember that you're putting wear and tear on your clutch and syncros just so you can slow down whereas you could be wearing down something much less valuable being your brakepads....
...I used to slow down alot by downshifting, if you get in the habit of doing this just remember that you're putting wear and tear on your clutch and syncros just so you can slow down whereas you could be wearing down something much less valuable being your brakepads....
Gratuitous double-declutch downshifting for a light or stop sign is unnecessary, but in fast driving and severe mountain descents it really is a good thing to do.
I've run out of brakes on a modern disc brake-equipped car descending the Grossglockner pass in Austria. So it's not always true that modern cars should just be slowed with their brakes.
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From: Abingdon, MD
Re: rétrogradage
Originally posted by Mike T.
If you downshift using a double-declutching technique...
If you downshift using a double-declutching technique...
I've only heard the term used in two places before. Old three-on-the-tree american manuals, and the movie "the fast and the furious". The later seemed to be used in error?
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
double declutching
Simply stated, a double-declutching technique is where the following sequence of events occurs:
1. clutch pedal depressed
2. with clutch pedal depressed, gearlever moved from higher gear to neutral
3. throttle blipped
4. with gearlever in neutral, clutch pedal is released
5. clutch pedal depressed a second time
6. lower gear engaged
7. clutch pedal released a second time
All this happens in a fraction of a second if you are practised at it, and the amount of the throttle blipping needed is a function of how quickly you can complete the above sequence. When you're quick, the blipping required will only be slightly more rpms that the engine would be spinning once the lower gear is engaged.
Some people rev-match on downshifts, which saves clutch disc wear but does not save the synchros. If you rev-match, then take the few days needed to learn double-declutching.
The purpose of the release of the clutch pedal in the middle of the shift combined with the throttle blip is to match the speeds of the mainshaft and layshaft inside the gearbox. If you don't double declutch, the synchromeshes do this gearbox shaft synchronisation for you. And this causes the synchromesh dogs to wear. Usually the second gear synchro is the first to go. A chronic downshifter who does not double-declutch can destroy a synchromesh unit in under 100,000 km (60,000 miles).
So if you do the above-noted actions properly, the input shaft and flywheel will be at almost exactly the same rpm when the clutch pedal is finally released, so the re-loaded clutch at the end of the shift will not wear appreciably since it does not have to drag the engine rpm up.
Hope that makes sense. It's easy to do but hard to write about.
1. clutch pedal depressed
2. with clutch pedal depressed, gearlever moved from higher gear to neutral
3. throttle blipped
4. with gearlever in neutral, clutch pedal is released
5. clutch pedal depressed a second time
6. lower gear engaged
7. clutch pedal released a second time
All this happens in a fraction of a second if you are practised at it, and the amount of the throttle blipping needed is a function of how quickly you can complete the above sequence. When you're quick, the blipping required will only be slightly more rpms that the engine would be spinning once the lower gear is engaged.
Some people rev-match on downshifts, which saves clutch disc wear but does not save the synchros. If you rev-match, then take the few days needed to learn double-declutching.
The purpose of the release of the clutch pedal in the middle of the shift combined with the throttle blip is to match the speeds of the mainshaft and layshaft inside the gearbox. If you don't double declutch, the synchromeshes do this gearbox shaft synchronisation for you. And this causes the synchromesh dogs to wear. Usually the second gear synchro is the first to go. A chronic downshifter who does not double-declutch can destroy a synchromesh unit in under 100,000 km (60,000 miles).
So if you do the above-noted actions properly, the input shaft and flywheel will be at almost exactly the same rpm when the clutch pedal is finally released, so the re-loaded clutch at the end of the shift will not wear appreciably since it does not have to drag the engine rpm up.
Hope that makes sense. It's easy to do but hard to write about.
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From: Abingdon, MD
It makes perfect sense as my '49 Ford Tudor required double clutching. I had just never heard of it used on a modern day car.
My MB C230 Sport Coupe crunches EVERY 1 - 2 shift. I am a chronic downshifter, I actually downshift more then I brake using throttle blipping to ease the lurching forward when downshifting.
I have 28k on my car and as I have said in earlier posts, it feels like my shifter is getting sloppier, much sloppier and as I said, it literally cruches every 1 - 2 shift more so when cold but becoming closer to every shift unless I double clutch it.
Any advice would be appreciated. (When I go to speak to my service dept. what do I say?)
My MB C230 Sport Coupe crunches EVERY 1 - 2 shift. I am a chronic downshifter, I actually downshift more then I brake using throttle blipping to ease the lurching forward when downshifting.
I have 28k on my car and as I have said in earlier posts, it feels like my shifter is getting sloppier, much sloppier and as I said, it literally cruches every 1 - 2 shift more so when cold but becoming closer to every shift unless I double clutch it.
Any advice would be appreciated. (When I go to speak to my service dept. what do I say?)
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From: Brisbane, Australia
C200K w203
"It's important to vary your engine speed when driving on the highway and not keep the car at a certian RPM for an extended period of time." by adamrs80
could some 1 pls explain to me why is that?
what about old cars?
could some 1 pls explain to me why is that?
what about old cars?
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From: BC, Canada
C230K
Re: double declutching
Originally posted by Mike T.
1. clutch pedal depressed
2. with clutch pedal depressed, gearlever moved from higher gear to neutral
3. throttle blipped
4. with gearlever in neutral, clutch pedal is released
5. clutch pedal depressed a second time
6. lower gear engaged
7. clutch pedal released a second time
[/B]
1. clutch pedal depressed
2. with clutch pedal depressed, gearlever moved from higher gear to neutral
3. throttle blipped
4. with gearlever in neutral, clutch pedal is released
5. clutch pedal depressed a second time
6. lower gear engaged
7. clutch pedal released a second time
[/B]
when clutch is still depressed?
or when cluth is released?
what i do when i downshift is, just keep depressing clutch, blip it, and to the lower gear.. so I only depress clutch once..
is that what u refer to rev-match?
Last edited by SB-ziV; May 14, 2003 at 06:46 AM.
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Originally posted by kingkong
"It's important to vary your engine speed when driving on the highway and not keep the car at a certian RPM for an extended period of time." by adamrs80
could some 1 pls explain to me why is that?
what about old cars?
"It's important to vary your engine speed when driving on the highway and not keep the car at a certian RPM for an extended period of time." by adamrs80
could some 1 pls explain to me why is that?
what about old cars?
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From: Ohio
2010 C300 4matic
Re: Re: double declutching
Originally posted by SB-ziV
So.. when do i exactly blip the throttle?
when clutch is still depressed?
or when cluth is released?
what i do when i downshift is, just keep depressing clutch, blip it, and to the lower gear.. so I only depress clutch once..
is that what u refer to rev-match?
So.. when do i exactly blip the throttle?
when clutch is still depressed?
or when cluth is released?
what i do when i downshift is, just keep depressing clutch, blip it, and to the lower gear.. so I only depress clutch once..
is that what u refer to rev-match?
Mike, I also want clarification on the first question. Aren't you supposed to blip the throttle after you release the clutch in neutral??
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
beh oui
Originally posted by Paul Le Corre
@Mike T: your 405?? do you speak about the peugeot 405??
@Mike T: your 405?? do you speak about the peugeot 405??
It's a Canadian model 405, originally called "405 DL" here but most similar to the 405 SRI in France. To confuse the curious, I placed a 405 SRI badge on it.
My favourite Peugeot is the 404 Coupé with Kugelfischer fuel injection, année modèle 1966, which is a restoration project.
Are you a Peugeot owner too?
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
Re: double declutching
Originally posted by Matt230K
Mike, I also want clarification on the first question. Aren't you supposed to blip the throttle after you release the clutch in neutral??
Mike, I also want clarification on the first question. Aren't you supposed to blip the throttle after you release the clutch in neutral??
I answered that question like a politician.OK, try again. Yes!
If you were only going to blip after the second declutching movement has begun, you are effectively doing a rev match, not a double-declutch. In order for the gearbox input shaft to be sped up, the engine needs to be blipped before/simultaneously with the momentary clutch release. That is what spins the input shaft up to the correct speed for the lower gear.
Told you it was hard to write about...
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From: Louisiana
E320
I used to switch gears without engaging the clutch at all by pulling out the gear right after I take my foot off the throttle, revematch, then throw the gear into place. Not always possible to do in all situations, but does that wear out the synchros too?
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From: Ohio
2010 C300 4matic
Re: Re: double declutching
Originally posted by Mike T.
If you were only going to blip after the second declutching movement has begun, you are effectively doing a rev match, not a double-declutch. In order for the gearbox input shaft to be sped up, the engine needs to be blipped before/simultaneously with the momentary clutch release. That is what spins the input shaft up to the correct speed for the lower gear.
Told you it was hard to write about...
If you were only going to blip after the second declutching movement has begun, you are effectively doing a rev match, not a double-declutch. In order for the gearbox input shaft to be sped up, the engine needs to be blipped before/simultaneously with the momentary clutch release. That is what spins the input shaft up to the correct speed for the lower gear.
Told you it was hard to write about...
Yes, hard to write about. Especially since I'm not completely familiar with the internals of a gearbox.
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
well
Originally posted by oggle
I used to switch gears without engaging the clutch at all by pulling out the gear right after I take my foot off the throttle, revematch, then throw the gear into place. Not always possible to do in all situations, but does that wear out the synchros too?
I used to switch gears without engaging the clutch at all by pulling out the gear right after I take my foot off the throttle, revematch, then throw the gear into place. Not always possible to do in all situations, but does that wear out the synchros too?
Shifting without a clutch is a good thing to know how to do in an emergency, but it's not good for the gearbox, especially when you make several mistakes...
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From: Ashburn, VA
'19 GLC 300, '19 TM3SR+
Re: well
Originally posted by Mike T.
... rev matching on a downshift without using the clutch is more nerve-wracking, but it is not too difficult....
... rev matching on a downshift without using the clutch is more nerve-wracking, but it is not too difficult....
Last edited by vadim; May 15, 2003 at 03:40 AM.
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
Re: double declutching
Originally posted by Matt230K
When the clutch is in, the engine is completely disconnected from the gearbox, right? So if you rev the engine and then release clutch, it will connect with gearbox shaft and spin it up to the same speed? If this is true, wouldn't blipping the throttle with the clutch out make the engine and the gearbox shaft spin up simultaneously, accomplishing the same thing? It seems like this would cause less wear???
When the clutch is in, the engine is completely disconnected from the gearbox, right? So if you rev the engine and then release clutch, it will connect with gearbox shaft and spin it up to the same speed? If this is true, wouldn't blipping the throttle with the clutch out make the engine and the gearbox shaft spin up simultaneously, accomplishing the same thing? It seems like this would cause less wear???
In any case, were almost dealing in hundredths of a second, so it all happens more or less at the same time anyway...
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From: Lilburn, GA, USA
1998 ML320
For another explanation with drawings showing foot-on-pedal placements, check this link to the TurnFast! web site. Read all the way down to get to the double-clutch section:
http://www.turnfast.com/tech_driving..._heeltoe.lasso
A good explanation with pictures can also be found in the book, "Bob Bondurant on High Performance Driving". It's been revised several times; I have an edition from about 25 years ago which I had my 16-year-old son read as part of his driver's education.
http://www.turnfast.com/tech_driving..._heeltoe.lasso
A good explanation with pictures can also be found in the book, "Bob Bondurant on High Performance Driving". It's been revised several times; I have an edition from about 25 years ago which I had my 16-year-old son read as part of his driver's education.
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From: Louisiana
E320
Re: well
Originally posted by Mike T.
Shifting without a clutch is a good thing to know how to do in an emergency, but it's not good for the gearbox, especially when you make several mistakes...
Shifting without a clutch is a good thing to know how to do in an emergency, but it's not good for the gearbox, especially when you make several mistakes...
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From: Abingdon, MD
Originally posted by shkeller55
For another explanation with drawings showing foot-on-pedal placements, check this link to the TurnFast! web site. Read all the way down to get to the double-clutch section:
http://www.turnfast.com/tech_driving..._heeltoe.lasso
A good explanation with pictures can also be found in the book, "Bob Bondurant on High Performance Driving". It's been revised several times; I have an edition from about 25 years ago which I had my 16-year-old son read as part of his driver's education.
For another explanation with drawings showing foot-on-pedal placements, check this link to the TurnFast! web site. Read all the way down to get to the double-clutch section:
http://www.turnfast.com/tech_driving..._heeltoe.lasso
A good explanation with pictures can also be found in the book, "Bob Bondurant on High Performance Driving". It's been revised several times; I have an edition from about 25 years ago which I had my 16-year-old son read as part of his driver's education.
Anyway, double clutching did nothing for my gear grinding issue. I have an appointment for June 11th figure out what's going on with the trans. However, the past two days, the issue has happened once.
For the clutch gurus, I've been practicing another shifting technique and I am curious of your anticipated effects. Basically it is designed to shave time off lap or drag slips. It's been refered to as speed shifting.
For upshifting.
basically, when you are shifting, you simply don't lift of the gas pedal. You depress the clutch just enough to make your shift, leaving the gas pedal mashed to the floor. It makes for super quick shifts, the car sort of jumps forward, but I am sure it can't good for the mechanical components.
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Originally posted by nukblazi
For upshifting.
basically, when you are shifting, you simply don't lift of the gas pedal. You depress the clutch just enough to make your shift, leaving the gas pedal mashed to the floor. It makes for super quick shifts, the car sort of jumps forward, but I am sure it can't good for the mechanical components.
For upshifting.
basically, when you are shifting, you simply don't lift of the gas pedal. You depress the clutch just enough to make your shift, leaving the gas pedal mashed to the floor. It makes for super quick shifts, the car sort of jumps forward, but I am sure it can't good for the mechanical components.
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From: Lilburn, GA, USA
1998 ML320
"Just to point out, this article is about heel-toe technique, which is very different from double clutching. The article describes the blip being referenced. "
If you had read all the way to the bottom of the article you would have seen that it does indeed describe double-clutching. And heel-toe technique is not "very" different; it is in fact very related in that you can't double-clutch properly if you don't employ the heel-toe technique properly.
If you had read all the way to the bottom of the article you would have seen that it does indeed describe double-clutching. And heel-toe technique is not "very" different; it is in fact very related in that you can't double-clutch properly if you don't employ the heel-toe technique properly.
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From: Lawng Island NY
2015 BMW 640ix GC (Ruby Black)
Very interesting...
thread. Just a couple of questions, if the posters would be so kind.
First, the just-referenced site (and I've always thought this) indicates that the "blipping" should be done with the clutch released. Now perhaps it makes no difference if the clutch is in, on the way out or fully out, and I'm no expert, but I really do think the clutch needs to be out when one blips in order to synchronize all the shafts.
Next, what do most people take as a "blip"? I double-clutched while downshifting for thirty years (don't know how well, though, although I never had to replace a clutch or gearbox), and blipped meant press and quick release of the throttle. After a brief sojourn with autos I just picked up my new manual car and everything I read now indicates "blip" means depress-and-hold throttle (until clutch is released). Perhaps it doesn't make any difference, I don't know.
Any pointers would be appreciated.
=NLK=
First, the just-referenced site (and I've always thought this) indicates that the "blipping" should be done with the clutch released. Now perhaps it makes no difference if the clutch is in, on the way out or fully out, and I'm no expert, but I really do think the clutch needs to be out when one blips in order to synchronize all the shafts.
Next, what do most people take as a "blip"? I double-clutched while downshifting for thirty years (don't know how well, though, although I never had to replace a clutch or gearbox), and blipped meant press and quick release of the throttle. After a brief sojourn with autos I just picked up my new manual car and everything I read now indicates "blip" means depress-and-hold throttle (until clutch is released). Perhaps it doesn't make any difference, I don't know.
Any pointers would be appreciated.
=NLK=
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From: Abingdon, MD
Originally posted by shkeller55
If you had read all the way to the bottom of the article you would have seen that it does indeed describe double-clutching. And heel-toe technique is not "very" different; it is in fact very related in that you can't double-clutch properly if you don't employ the heel-toe technique properly.
If you had read all the way to the bottom of the article you would have seen that it does indeed describe double-clutching. And heel-toe technique is not "very" different; it is in fact very related in that you can't double-clutch properly if you don't employ the heel-toe technique properly.
In regards to technique, individually, and conceptually, they seem distinctly different. One requiring the other doesn't merge the techniques or make them the same.
Heel-toe technique is operating the brake and gas at the same time when braking into a turn. So as you employ heel-toe going into the corner, you use you heel to blip the gas while double-clutching. This is employing two techniques at the same time, not one. No?
We have assumed the use of a street car, and a street transmission with synchros. If you're using a true race transmission without synchros, then you need to modify the above shifting with a double-clutch procedure. To do this, the clutch is pressed in, the shifter moved to neutral...
Last edited by nukblazi; May 19, 2003 at 06:07 PM.
