Question regarding the double-clutching topic.

[Shawn]

Originally posted by: Skoorb

Originally posted by: Sqube
Wow... interesting thread and a lot of subtly different explanations. Which doesn't help for people trying to understand.

If you are at 4k in 2nd gear and want to go into 3rd gear and 3rd gear, at this speed, would be about 3k RPM, normally you just put the clutch in and move from 2nd to 3rd. Double clutching would involve you putting the clutch in, moving to neutral, letting the clutch off, revving the engine to 3k, then putting the clutch in again, then move it to 3rd, then disengage the clutch and you're finally in third.

Other than a few circumstances like if dainbramaged wants to get into 1st, there is never a reason to double clutch on a modern transmission.

Why do you have to shift into neutral and let go of the clutch? Couldn't you just hold the clutch in and rev match then let go of the clutch? Would this do the same thing?

 

[skyking]

Originally posted by: Shawn

Originally posted by: Skoorb

Originally posted by: Sqube
Wow... interesting thread and a lot of subtly different explanations. Which doesn't help for people trying to understand.

If you are at 4k in 2nd gear and want to go into 3rd gear and 3rd gear, at this speed, would be about 3k RPM, normally you just put the clutch in and move from 2nd to 3rd. Double clutching would involve you putting the clutch in, moving to neutral, letting the clutch off, revving the engine to 3k, then putting the clutch in again, then move it to 3rd, then disengage the clutch and you're finally in third.

Other than a few circumstances like if dainbramaged wants to get into 1st, there is never a reason to double clutch on a modern transmission.

Why do you have to shift into neutral and let go of the clutch? Couldn't you just hold the clutch in and rev match then let go of the clutch? Would this do the same thing?

no.
You are spinning up the front half of the transmission to match a particular gear ratio in the back half, then moving the syncro across once the speeds are matched. You have to re-engage the clutch.

 

[huesmann]

There's no point in double-clutching a modern tranny. You get the same effect by waiting for the revs to come down on an upshift to match the speed of the gear you're shifting to, or rev-matching by heel-and-toeing a downshift.

 

[alkemyst]

i want to be like Vin Diesel too?

 

[Zenmervolt]

Originally posted by: TwoBills

Originally posted by: Zenmervolt
You're wrong about the brakes. Properly executed, a double-clutch downshift is rev-matched perfectly and there is _ZERO_ drivetrain shock since all rotating componants are synchronized through double-clutching and rev-matching even without using the brakes.

ZV

That's true, but if you're double clutching as part of your normal slowing down routine, then I think it's more economical, in the long run, to use the brakes more. I prefer burning off the speed with the brakes, and then execute a 5-3 or a 4-2 dc. I never gear down to slow down, that's what the brakes are for, with some exceptions.

Oh, I completely agree. On the track I'm heel-toing down through the gears and _HARD_ on the brakes when coming into a corner (as Mario once said, "slow in, fast out") but your claim that they would shock the drivetrain by not using the brakes isn't correct.

And on the street, I usually just leave it in whatever gear I'm in when I start braking and don't shift until I hit idle speed.

ZV

 

[cavemanmoron]

Originally posted by: CRXican
why would you ever downshift to 1st at 25mph?

hmm, depends on final gearing of the car.

I had a 68 GTX 4 speed that was geared tall,and I could use first gear till about 35,
top end was too fast.
I gave up at 140mph,speedo was a 150.!!

 

[TwoBills]

Originally posted by: Zenmervolt

Originally posted by: TwoBills

Originally posted by: Zenmervolt
You're wrong about the brakes. Properly executed, a double-clutch downshift is rev-matched perfectly and there is _ZERO_ drivetrain shock since all rotating componants are synchronized through double-clutching and rev-matching even without using the brakes.

ZV

That's true, but if you're double clutching as part of your normal slowing down routine, then I think it's more economical, in the long run, to use the brakes more. I prefer burning off the speed with the brakes, and then execute a 5-3 or a 4-2 dc. I never gear down to slow down, that's what the brakes are for, with some exceptions.

Oh, I completely agree. On the track I'm heel-toing down through the gears and _HARD_ on the brakes when coming into a corner (as Mario once said, "slow in, fast out") but your claim that they would shock the drivetrain by not using the brakes isn't correct.

And on the street, I usually just leave it in whatever gear I'm in when I start braking and don't shift until I hit idle speed.

ZV

Sometimes I have trouble making myself clear when typing a response. You're completely right, of course. Saving the drivetrain is what dcing is all about. I was talking more to the *cough* young driver that has yet to learn the pleasures involved with replacing their 1st tranny/clutch/bottom end.

I'll bet it would be a hoot to do a few laps w/you, ZV, in my work truck.

 

[Zenmervolt]

Originally posted by: cavemanmoron

Originally posted by: CRXican
why would you ever downshift to 1st at 25mph?

hmm, depends on final gearing of the car.

I had a 68 GTX 4 speed that was geared tall,and I could use first gear till about 35,
top end was too fast.
I gave up at 140mph,speedo was a 150.!!

35 in first is tall? The gearing on the AOD-EW transmission in my MarkVIII is insane. I know it's an auto, but she'll hold 1st until 55. Still runs to 60 in about 7 seconds. I would _love_ to see what she'd do with a 4.11 rear end, but I'd need way more rubber for that. Still, it's a great car. Two tons of American fun. Would rather have a '65 'Stang though. Drop in a 351W and use that as the grocery getter.

TwoBills: I'll bet it would be. I haven't spent time at a track since moving to Seattle and I'm sure that I'm rusty right now (the 944 is still home in Ohio, awaiting my purchase of a place with a garage) but it's never bad to get out on a track.

ZV

 

[TwoBills]

Originally posted by: Zenmervolt

Originally posted by: cavemanmoron

Originally posted by: CRXican
why would you ever downshift to 1st at 25mph?

hmm, depends on final gearing of the car.

I had a 68 GTX 4 speed that was geared tall,and I could use first gear till about 35,
top end was too fast.
I gave up at 140mph,speedo was a 150.!!

35 in first is tall? The gearing on the AOD-EW transmission in my MarkVIII is insane. I know it's an auto, but she'll hold 1st until 55. Still runs to 60 in about 7 seconds. I would _love_ to see what she'd do with a 4.11 rear end, but I'd need way more rubber for that. Still, it's a great car. Two tons of American fun. Would rather have a '65 'Stang though. Drop in a 351W and use that as the grocery getter.

TwoBills: I'll bet it would be. I haven't spent time at a track since moving to Seattle and I'm sure that I'm rusty right now (the 944 is still home in Ohio, awaiting my purchase of a place with a garage) but it's never bad to get out on a track.

ZV

Hell of a grocery getter. In my younger days I had a '65. It's what I learned what not to do on. Moved to a Boss 302 after that. Fast machine. Lucky I'm still around. Presently my work truck is a Nissan Frontier (SC of course). Sucker'll roll down the hwy, but the brakes are a little lacking. My old truck was a Mitsubishi sport. Factory 2.6L leaker, but that sucker could brake. Could get 110k out of a set of brakes, w/a 600lb load and brakin' hard (I'm a firm believer in not piddlin' w/the brakes, use 'em or lose 'em). It became "farm use only" after I out braked a county cop and she ran up my ass. Puttin' her make up on, or something.

 

[SWScorch]

I didnt read all of this thread because I'm lazy, but why would you double clutch instead of just putting the clutch, in, rev the engine to the proper rpm, shift and then take the clutch out? Why do you have to cluth in, clutch out in neutral, then rev, then clutch in, shift to new gear, clutch out? When I downshift I rev-match, that is, I blip the accelerator to get the engine to the proper rpm so when I release the clutch it doesn't lurch. isnt that good enough?

 

[LS20]

Originally posted by: SWScorch
I didnt read all of this thread because I'm lazy, but why would you double clutch instead of just putting the clutch, in, rev the engine to the proper rpm, shift and then take the clutch out? Why do you have to cluth in, clutch out in neutral, then rev, then clutch in, shift to new gear, clutch out? When I downshift I rev-match, that is, I blip the accelerator to get the engine to the proper rpm so when I release the clutch it doesn't lurch. isnt that good enough?

rev-matching alone saves wear on the clutch (tranny/motor interface) ... not the gears /tranny internals

Originally posted by: huesmann
There's no point in double-clutching a modern tranny. You get the same effect by waiting for the revs to come down on an upshift to match the speed of the gear you're shifting to, or rev-matching by heel-and-toeing a downshift.

do you know what you're talking about?