I have always wondered what happens during a double clutch, so lets work through it.
Lets say you are at 3000 RPM in 4th to downshift to 3rd you:
A- Depress the clutch: this decouples the engine from the trans
move gear from 4th to neutral: slider ring decoupled final drive from input shaft.
The input shaft is now spinning down under friction (was just at 3000 RPM input).
B- While shifting out of gear you started to bring the engine revs UP in anticipation of the shift.
C- You release the clutch: this recouples the engine to the trans input shaft so you are bringing the shaft up to whatever speed the engine is at
you continue to raise the engine (and input shaft up in RPM) while in neutral.
D- Now you depress the clutch again decoupling the engine & input shaft.
E- Now you move the slider into 3rd gear where the synchros guarantee input shaft at ~4000 RPM before engagement.
F- Now you release the clutch and are in 3rd at 4000 RPM
Now lets work through a regular shift:
You are at 3000 RPM in 4th to downshift to 3rd you:
A- Depress the clutch: this decouples the engine from the trans
move gear from 4th to neutral: slider ring decoupled final drive from input shaft.
The input shaft is now spinning down under friction (was just at 3000 RPM input).
B- While shifting out of gear you started to bring the engine revs UP in anticipation of the shift.
C - you move the shift lever to 3rd and the sychros bring the input shaft speed up to match the speed of the 3rd gear (4000 RPM).
D- Now you release the clutch and are in 3rd at 4000 RPM
I just have a hard time believing, that a human can negotiate all of the above in the split second that I can perform a "regular" downshift.
In fact I think I can demonstrate a downshift with no clutch about the same speed as a double clutch.
I have a theory that people who are really in tune with their car do not even disengage the clutch all the way during every shift, but dont even realize it until the rare time where you grind and wonder "what was up with that...."
Not only do I not get the theory behind the double clutch, but I have tried it, and I see no advantage whatsoever except to make me shift slower which makes it smoother.
That is the same effect as just shifting slower without double clutching.
So I can see a slight advantage where there is slightly less wear on the synchros. If you are so worried about your synchros that you will use
an antiquate driving technique, then just do the whole trans a favor and dont drive so much.
And all of the examples above about having trouble downshifting into 1st - it's like the doctor says "if it hurts when you do that,
stop doing that".
In the parts diagram for the trans, 1st gear is the ONLY gear that has a part called a "1st gear lockout". I wonder what that is for?
Maybe to make it hard to downshift to first because they
dont what you to do that.
I never see a need to downshift to 1st.
If the car is even moving at all, I can get going again in 2nd without bogging much.
Quote:
Originally Posted by Ultramaroon
You know I'm not talking about the track. What's the point of bringing that up again? No one double-clutches on the track unless they've acquired one of Skip Barber's old cars.
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Because if it was a technique that had any benefit whatsoever, I think I would hear about someone using it at the track. The truth is - there is absolutely zero reason to use double clutching on a modern trans unless you are doing it purely to slowdown your shifts (it performs that function well) to reduce wear on your trans.
I have a method to reduce wear on your tires: Every time you stop it with hot tires, put it up on jackstands
