Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM
Posted:
Tue Jan 05, 2010 2:28 pm
arun wrote:
Double clutching should be avoided in commercial cars as its surely damages the transmission and wears out soon, so its economically not appreciable to do double clutching and shifting.
Please provide a clear technical explanation of EXACTLY how double clutching causes additional wear.
Joined: Jan 11, 2010
Posts: 5
Location: Las Vegas, NV
Posted:
Mon Jan 11, 2010 10:06 pm
I think it's a waste of energy and fairly pointless to double clutch in a car.
In fact, even when I did drive a commercial truck, most of the guys that had been on the road for a while used float shifting. Some companies even had a policy in favor of floating rather than double clutching.
Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM
Posted:
Tue Jan 12, 2010 12:58 am
EYEAM4ANARCHY wrote:
I think it's a waste of energy and fairly pointless to double clutch in a car.
In fact, even when I did drive a commercial truck, most of the guys that had been on the road for a while used float shifting. Some companies even had a policy in favor of floating rather than double clutching.
Not really.
Every time you shift with a synchromesh transmission, you cause some wear to the synchronizers. Once I bought a new 1975 Mazda RX4. That model was known to have synchronizers which tended to wear out quickly, so I decided that to preserve the synchronizers, I would double clutch all downshifts. A couple years later, I bought another new car and gave the Mazda to my sister. I warned her that the synchronizers were weak and that unless she double clutched all the downshifts, the synchronizers would fail. She was unwilling to learn how to double clutch, and the synchronizers did fail. After that, the gears would grind on downshifts unless it was double clutched, so she had no choice but to learn how to do it.
Granted that late model cars have more durable synchromesh, but even so, the wear can be reduced by double clutching all downshifts, especially when downshifting at higher speeds. Downshifting at high speeds is necessary for passing on the highway, unless you don't mind feeling like a sitting duck. So, if you plan to keep the car for a long time, it is a good idea to double clutch the downshifts.
Of course you can float the gears even if you have synchromesh, but unless you are highly skilled, that will increase the wear on the synchronizers. On a few different cars, I've had to float the gears when the clutch failed. On my father's 1953 Austin Healey, the clutch linkage broke. On my mother's 1950 Chevrolet, a segment of the clutch lining came loose and jammed between the plates, making it impossible to disengage the clutch. On my 1971 Porsche 914, the clutch cable broke. Also, on older cars with a 3-speed manual transmission, 1st gear is not synchronized so to shift to 1st with the car moving, you have to double clutch. Until 1961, Volkswagens didn't have synchromesh on 1st gear. Most people never learned to double clutch and thought that you had to stop before shifting to 1st gear.
There is no need to double clutch, the racers only do it because they don't have synchros (synchromesh gears) on their gearbox - to them, its just another thing to break. Street cars however do, its a matter of convenience, there is just not enough stress on the tranny during street driving to justify the extra effort.
Now if you shift really hard all the time, you will wear out the synchros faster.
If you double clutch and you have synchros... you will just be the butt end of a bad joke
Racing downshifting on the other hand is better. They do heel toe downshifting to rev match their car. Not only does it stop the 'lurch' that manual transmissions have, it also saves wear and tear on the clutch plate because the clutch does not have to spin up the engine speed to match the transmission speed
Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM
Posted:
Wed Mar 17, 2010 1:22 am
Chris wrote:
There is no need to double clutch, the racers only do it because they don't have synchros (synchromesh gears) on their gearbox - to them, its just another thing to break. Street cars however do, its a matter of convenience, there is just not enough stress on the tranny during street driving to justify the extra effort.
Now if you shift really hard all the time, you will wear out the synchros faster.
If you double clutch and you have synchros... you will just be the butt end of a bad joke
Racing downshifting on the other hand is better. They do heel toe downshifting to rev match their car. Not only does it stop the 'lurch' that manual transmissions have, it also saves wear and tear on the clutch plate because the clutch does not have to spin up the engine speed to match the transmission speed
True, there USUALLY is no need to double clutch with a MODERN car, UNLESS you want to maximize the life of the synchronizers. And, it does not make one the but of jokes. It couldn't since most people don't even know what double clutching is.
I remember someone who had a 1953 Kaiser. The synchromesh on 2nd gear had failed and he had a terrible time with it until I taught him how to double clutch. Also, at one time, no American car with a 3-speed manual transmission had synchromesh on 1st gear. Most people didn't know how to double clutch and thought that you had to stop before shifting to 1st gear but actually, those of us who know how to double clutch had no trouble shifting to 1st gear, without grinding the gears, even while the car was moving.
As for race cars not having synchromesh, that is not true, unless you eliminate all older race cars. That's like saying that it is impossible to start a car with an automatic transmission by pushing it. I can assure you that all cars with automatic transmissions made before 1956 could be started by pushing, just as all race cars at one time had synchromesh.
There is no need to double clutch, the racers only do it because they don't have synchros (synchromesh gears) on their gearbox - to them, its just another thing to break. Street cars however do, its a matter of convenience, there is just not enough stress on the tranny during street driving to justify the extra effort.
Now if you shift really hard all the time, you will wear out the synchros
faster.
If you double clutch and you have synchros... you will just be the butt end of a bad joke
Racing downshifting on the other hand is better. They do heel toe downshifting to rev match their car. Not only does it stop the 'lurch' that manual transmissions have, it also saves wear and tear on the clutch plate because the clutch does not have to spin up the engine speed to match the transmission speed
True, there USUALLY is no need to double clutch with a MODERN car, UNLESS you want to maximize the life of the synchronizers. And, it does not make one the but of jokes. It couldn't since most people don't even know what double clutching is.
I remember someone who had a 1953 Kaiser. The synchromesh on 2nd gear had failed and he had a terrible time with it until I taught him how to double clutch. Also, at one time, no American car with a 3-speed manual transmission had synchromesh on 1st gear. Most people didn't know how to double clutch and thought that you had to stop before shifting to 1st gear but actually, those of us who know how to double clutch had no trouble shifting to 1st gear, without grinding the gears, even while the car was moving.
As for race cars not having synchromesh, that is not true, unless you eliminate all older race cars. That's like saying that it is impossible to start a car with an automatic transmission by pushing it. I can assure you that all cars with automatic transmissions made before 1956 could be started by pushing, just as all race cars at one time had synchromesh.
Thanks for correcting me on that. I SHOULD have said modern race cars haha. My mind and keyboard didn't quite sync up. And +1 on usually not needing to double clutch, one of my friends has a similar problem. As for the jokes, I was talking about the various ricer jokes
Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM
Posted:
Wed Mar 17, 2010 11:02 pm
Chris wrote:
FRE wrote:
Chris wrote:
There is no need to double clutch, the racers only do it because they don't have synchros (synchromesh gears) on their gearbox - to them, its just another thing to break. Street cars however do, its a matter of convenience, there is just not enough stress on the tranny during street driving to justify the extra effort.
Now if you shift really hard all the time, you will wear out the synchros
faster.
If you double clutch and you have synchros... you will just be the butt end of a bad joke
Racing downshifting on the other hand is better. They do heel toe downshifting to rev match their car. Not only does it stop the 'lurch' that manual transmissions have, it also saves wear and tear on the clutch plate because the clutch does not have to spin up the engine speed to match the transmission speed
True, there USUALLY is no need to double clutch with a MODERN car, UNLESS you want to maximize the life of the synchronizers. And, it does not make one the but of jokes. It couldn't since most people don't even know what double clutching is.
I remember someone who had a 1953 Kaiser. The synchromesh on 2nd gear had failed and he had a terrible time with it until I taught him how to double clutch. Also, at one time, no American car with a 3-speed manual transmission had synchromesh on 1st gear. Most people didn't know how to double clutch and thought that you had to stop before shifting to 1st gear but actually, those of us who know how to double clutch had no trouble shifting to 1st gear, without grinding the gears, even while the car was moving.
As for race cars not having synchromesh, that is not true, unless you eliminate all older race cars. That's like saying that it is impossible to start a car with an automatic transmission by pushing it. I can assure you that all cars with automatic transmissions made before 1956 could be started by pushing, just as all race cars at one time had synchromesh.
Thanks for correcting me on that. I SHOULD have said modern race cars haha. My mind and keyboard didn't quite sync up. And +1 on usually not needing to double clutch, one of my friends has a similar problem. As for the jokes, I was talking about the various ricer jokes
Thanks for the reply.
Once I had a 1975 Mazda RX4. That model was known to have synchronizers that didn't last long, so I decided to double clutch all my downshifts; I never had a problem with it. Later, when my sister had the car, I warned her about the short-lived synchros and advised her to double clutch, but she couldn't be bothered to learn. So, the synchronizers soon failed after which she had no choice but to learn to double clutch.
My father had a 1953 Austin Healey with rather weak synchronizers. One could downshift to 1st gear by feeling it in carefully to give the synchronizer time to work, but it was actually faster to double clutch it.
In my opinion, whether one needs to double clutch or not, it is a good skill to master. It isn't difficult if there are synchronizers which can at least compensate for minor errors.
Gosh, I won't quote all that text... But quick question since you have experience in that area - how do you double clutch and downshift? Take your foot off the brake to operate the clutch? Heel toe - style? What?
Joined: Oct 05, 2008
Posts: 79
Location: Albuquerque NM
Posted:
Wed Mar 17, 2010 11:45 pm
Chris wrote:
Gosh, I won't quote all that text... But quick question since you have experience in that area - how do you double clutch and downshift? Take your foot off the brake to operate the clutch? Heel toe - style? What?
It depends on the car. I prefer heel - toe double clutching, but because of the way that the brake and accelerator are positioned on some cars, it isn't always possible. Of course when one is quickly shifting from 5th to 3rd to get more acceleration for passing, one's foot isn't on the brakes anyway. But when slowing down, it's awkward if one cannot heel - toe it.
Gosh, I won't quote all that text... But quick question since you have experience in that area - how do you double clutch and downshift? Take your foot off the brake to operate the clutch? Heel toe - style? What?
It depends on the car. I prefer heel - toe double clutching, but because of the way that the brake and accelerator are positioned on some cars, it isn't always possible. Of course when one is quickly shifting from 5th to 3rd to get more acceleration for passing, one's foot isn't on the brakes anyway. But when slowing down, it's awkward if one cannot heel - toe it.
Joined: Aug 02, 2006
Posts: 705
Location: McLean, VA, USA
Posted:
Sun Jun 13, 2010 4:15 pm
Hi Nofon, and welcome to FaSD!
Back in the times when there were no such thing as a synchronized gearbox everybody knew this. It is the technique designed to equalize the rotational speeds of gears during the process of changing gears.
Nowadays used on some racing cars where weight considerations are very strict, and by teens who want to be cool.
Cars and pickups have what they call synchronizers in the transmission. They cause the gears to run the same speed before engaging, so there is no need to double clutch. However, semi trucks don't have synchros, so double clutching is almost a necessity
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