double clutching, does it help?
Team Owner
Joined: Aug 2004
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From: Park City Utah
And slipping the clutch/pp/fw (when releasing in neutral) increases wear? I don't think so. Certainly not when compared to the wear incured by releasing the clutch in the lower gear, to an un-synchronized engine speed.
As for synchro's being standard since the 20's, my '83 Jeep J-20 had a non-synchronized first gear. I'll give you one guess as to how I managed to get it in that gear on the move, w/o grinding....
Last edited by Tom400CFI; Jul 31, 2007 at 07:15 PM.
Le Mans Master
Joined: Oct 2004
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From: South-central Missouri
Indeed, you ARE matching speeds. All the gears are in constant mesh, but, if the speeds didn't need to be matched, you would be in the gear you wanted. You, by double clutching, or the synchros, aren't matching the mainshaft gear speed with the countershaft (cluster) gear speed, because as you said, they are already meshed. BUT you DO have to match the mainshaft gear speed with that of the mainshaft. In order for the teeth of the sliding clutch (the sleeve the shift fork moves) to slide over the clutching teeth of the mainshaft gear, they have to be moving at the same (synchronized) speed. The sliding clutch is splined to the mainshaft. When the sliding clutch slips over the clutching teeth of the mainshaft gear, it locks the mainshaft gear to the mainshaft. Because they are in constant mesh with the countershaft gears, they have to freewheel on the mainshaft until selected. Clear as mud?
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RACE ON!!!
P.
Team Owner
Joined: Mar 2001
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From: Cincinnati, Oh USA
Again, I am not commenting on the desirability or value of double clutching, just on how the transmission works.
By that same logic, an engine would never need new main or rod bearings. Sure, the oil film helps, but if the oil were the only braking force in the synchro system, the material of the stop rings would never be a consideration, which it is. I'd like a nickle for every synchro ring I've ever sold.
My 1929 Model A Ford was an all sliding gear, non-synchronized crash box. I think you are about 20 years early in your "Synchronizers became standard equipment in manual transmissions" statement. Although transmissions existed that had it, first gear was never universally synchro in a three speed.
RACE ON!!!
By that same logic, an engine would never need new main or rod bearings. Sure, the oil film helps, but if the oil were the only braking force in the synchro system, the material of the stop rings would never be a consideration, which it is. I'd like a nickle for every synchro ring I've ever sold.
My 1929 Model A Ford was an all sliding gear, non-synchronized crash box. I think you are about 20 years early in your "Synchronizers became standard equipment in manual transmissions" statement. Although transmissions existed that had it, first gear was never universally synchro in a three speed.
RACE ON!!!
You are right about 1st gear in 3 speeds, all my cars had sliding gears in 1st until my 69 vette. I am very sure that very late 20's, synchros began use in manual transmissions except 1st gear, I'm too lazy to look it up. Ferrari has synchros even in reverse! (some models, not all)
Team Owner
Joined: Mar 2001
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From: Cincinnati, Oh USA
Talk about pedantic. Blipping the throttle increases engine wear?? Can you quantify the extent of that wear please? W/documentation? lol.
And slipping the clutch/pp/fw (when releasing in neutral) increases wear? I don't think so. Certainly not when compared to the wear incured by releasing the clutch in the lower gear, to an un-synchronized engine speed.
As for synchro's being standard since the 20's, my '83 Jeep J-20 had a non-synchronized first gear. I'll give you one guess as to how I managed to get it in that gear on the move, w/o grinding....
And slipping the clutch/pp/fw (when releasing in neutral) increases wear? I don't think so. Certainly not when compared to the wear incured by releasing the clutch in the lower gear, to an un-synchronized engine speed.
As for synchro's being standard since the 20's, my '83 Jeep J-20 had a non-synchronized first gear. I'll give you one guess as to how I managed to get it in that gear on the move, w/o grinding....
My first 2 cars had sliding 1st gears and I too could engage them underway without grinding. You aren't the only one who knows how!
Team Owner
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St. Jude Donor '10
Team Owner
Joined: Aug 2004
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From: Park City Utah
Indeed, it IS insignificant, and unmeasurable.
Yep insignificant, and unmeasureable. Especially when compared to the wear on the clutch when, as I stated above:
...Wear to the clutch face is no more, during a proper double clutch down shift, than it is letting the pedal out when stopped, idling in neutral after taking the shifter out of gear! You might want to warn people about the potential detriments of THAT practice too! lol.
No where, did I say that I was. I simply said:
I'm not going to bore you w/"Tom's history of cars" as you did above, but I've owned several w/over 200k I've never replaced bearing shells (in these cars), or synchros. My point is with regard to parts wear, double clutching vs. not, it doesn't f'n matter one way or the other. It's "6's". So a driver might as welll shift how ever he feels prudent, given the situation at hand. Worrying about wear to the car, one way or the other, will actually wear out your brain more than any wear applied to the car, either way that you choose to shift!
I wasn't arguing that double clutching is "less wear", I was just raising the "BS flag" to jfb's post that one style of shifting (discussed in this thread) imparts more total, and measurable wear to the car than another. It doesn't, so just shift how you want.
Originally Posted by Tom400CFI
Certainly not when compared to the wear incured by releasing the clutch in the lower gear, to an un-synchronized engine speed.
Originally Posted by Tom400CFI
I'll give you one guess as to how I managed to get it in that gear on the move, w/o grinding....
I'm not going to bore you w/"Tom's history of cars" as you did above, but I've owned several w/over 200k I've never replaced bearing shells (in these cars), or synchros. My point is with regard to parts wear, double clutching vs. not, it doesn't f'n matter one way or the other. It's "6's". So a driver might as welll shift how ever he feels prudent, given the situation at hand. Worrying about wear to the car, one way or the other, will actually wear out your brain more than any wear applied to the car, either way that you choose to shift!
I wasn't arguing that double clutching is "less wear", I was just raising the "BS flag" to jfb's post that one style of shifting (discussed in this thread) imparts more total, and measurable wear to the car than another. It doesn't, so just shift how you want.
Last edited by Tom400CFI; Aug 1, 2007 at 11:03 AM.
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Pro
Joined: Aug 2006
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From: SpringHill florida
i dont wonna be the dirtbag to bring this up but in our fav. movie "the slow and the curious" Vin diesel said that the guy was granny shifting instead of double clutching,but double clutching seems to be alot slower the normal driving,can someone explain?
Racer
Joined: Feb 2006
Posts: 269
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From: Vancouver B.C.
Vin Diesel's statement was idiotic. Poor screenwriting.
What he SHOULD have said was 'speed-shifting'.....not 'double clutching'.
Double clutching is only for down-shifting, in order to smooth out the different rpm's between engine/transmission/vehicle enertia. (as many here have explained)
Speed shifting is at WOT, clutch depressed/released quickly while at the same second shifting into higher gear. Not for the faint of heart. Or the thin of wallet. NOT recommended unless .005 second time savings is needed.
What he SHOULD have said was 'speed-shifting'.....not 'double clutching'.
Double clutching is only for down-shifting, in order to smooth out the different rpm's between engine/transmission/vehicle enertia. (as many here have explained)
Speed shifting is at WOT, clutch depressed/released quickly while at the same second shifting into higher gear. Not for the faint of heart. Or the thin of wallet. NOT recommended unless .005 second time savings is needed.
Last edited by Carpenter; Aug 1, 2007 at 11:28 AM.
Safety Car
Joined: May 2006
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From: Salem NH
Some things to keep in mind:
Input shafts sometimes taper with wear, and drag on 15+ year old pilot bushings.
Any time you step on the clutch, something is wearing. Which is why sitting at a traffic light with the clutch in is silly.
Now my opinion..
I've never double-clutched a car. A few big trucks, for downshifting, but never a car. I have worked the throttle between gears downshifting. For up shifting, if the input shaft is within spec and BEARING good, the RPMS on a modern motor should fall immediately.
I've 'speed shifted' for many many years at the track, never had a problem. And we're not talking lame street clutches, we're talking ceramic padal clutches, 1600+ lbs pressure plates, and slicks
On my current car, the Corvette, the auto hits harder than I ever did on a stick. go figure..
-- Joe
Input shafts sometimes taper with wear, and drag on 15+ year old pilot bushings.
Any time you step on the clutch, something is wearing. Which is why sitting at a traffic light with the clutch in is silly.
Now my opinion..
I've never double-clutched a car. A few big trucks, for downshifting, but never a car. I have worked the throttle between gears downshifting. For up shifting, if the input shaft is within spec and BEARING good, the RPMS on a modern motor should fall immediately.
I've 'speed shifted' for many many years at the track, never had a problem. And we're not talking lame street clutches, we're talking ceramic padal clutches, 1600+ lbs pressure plates, and slicks
On my current car, the Corvette, the auto hits harder than I ever did on a stick. go figure..
-- Joe
Team Owner
Joined: Mar 2001
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From: Cincinnati, Oh USA
In the days when transmissions did not have synchronizers and the driver HAD to double clutch to downshift, the driver got immediate feedback if he/she didn't do it right and learned from that noisy experience and became better at it. Now if you double clutch a modern transmission that does have synchronizers in it, you get absolutely no feedback, and therefore your skill at matching the transmission input shaft speed to the selected gear speed cannot be enhanced and the driver really has not the slightest idea if the speeds were matched. If you don't have an indication that your downshift was done properly to negate the job of the synchronizer, then why in the world would you do it?
Team Owner
Joined: Aug 2004
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From: Park City Utah
When you shift, you can feel the "resistance" of the synchronizer as it takes a period of time for it to synchronize shaft speeds. The faster or harder that you try to shift, the more this can be felt.
When you double clutch properly, matching RPM's closely, there is no resistance felt by the synchronizers at all; just the detent in the shifting mechanism, and it is a noticably smoother action.
You CAN feel the difference, there IS a reward, both in shifting feel, and in general driver/shift smoothness when the clutch is released in the lower gear: the passengers head won't bob forward when you release the clutch in the lower gear.
Again, I'm not saying that there is a right way and a wrong way to shift; rather that what was just posted in the quote above is incorrect information. jfb's right hand must be numb.
Last edited by Tom400CFI; Aug 1, 2007 at 12:38 PM.
Team Owner
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From: Cincinnati, Oh USA
I don't double clutch and I also don't feel any resistance well above normal to downshifting in my 87 vette. The only significant resistance to downshifting I have ever experienced is when I have tried to downshift into 1st gear. Maybe your transmission is screwed up!
Team Owner
Joined: Aug 2004
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From: Park City Utah
The transmission in my '06 'Vette isn't "screwed up". Nor is the 5 speed in my '96 Silverado. Niether were the 3 Trans's in my Trans Am, or the T-56 in my '86 Camaro. Or the T-18 in my J-truck, or the 4 speed in my long gone '86 Dodge Colt. Yet they ALL exhibited that same characteristic:
^That one. You just hit on what I was describing. Exagerated, in your case by trying to hit 1st gear at too high a speed, the resistance was cause by the blocking rings trying to accomodate the massive speed differential between your trans main shaft speed, and the speed of the first gear/clutch disk speed. By posting what you just did, you're PROVING that the closer you match the speeds of these components, the smoother engagement you will feel.
You don't "feel any resistance well above normal" because it's NOT "above normal" (and I wasn't saying that it was above "normal"), and because:...so you don't know the difference. Either that or your right hand is numb.
Either way, the facts are that...
You don't "feel any resistance well above normal" because it's NOT "above normal" (and I wasn't saying that it was above "normal"), and because:...so you don't know the difference. Either that or your right hand is numb.
Either way, the facts are that...
Originally Posted by Tom400CFI
there IS a reward, both in shifting feel, and in general driver/shift smoothness when the clutch is released in the lower gear: the passengers head won't bob forward when you release the clutch in the lower gear.
Last edited by Tom400CFI; Aug 1, 2007 at 04:59 PM.
Thread Starter
Le Mans Master
Joined: Apr 2005
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From: The Old Dominion
You seem to be taking this fairly personally. I don't think anyone said your car will fail early if you shift normally, or that a person can't have a transmission last the life of the car unless they double clutch. Nor was that the intent of my question.
I wondered if it can help, sounds like it can, and if there's any down side, sounds like there isn't.
Racer
Joined: Feb 2006
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From: Vancouver B.C.
I had a VW bug when I was 16. Clutch 'quit'.....so for 6 months I drove it around without one. I'd start it in 1st.(yes, it actually started! and 6 volt too!) then 'feel' my way up and down the grears....would downshift back into 1st. and judge the light (or traffic) then simply carry on. My personal challenge was to never grind any gears.....which I accomplished after only a few hours of practice.
But that was when I was young and could multi-task. Now-a-days I'm doing good if I remember to turn off my ASR.
But that was when I was young and could multi-task. Now-a-days I'm doing good if I remember to turn off my ASR.
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Not to mention the ZF cylinders and throwout bearing are all POS parts. I would shift normally. Blipping the throttle during downshifts is done so you don't upset the balance of the car by lurching the motor up in rpms. This will cause you to loose the rear end going into a corner if you're running on the ragged edge.