If you can't downshift smoothly without double clutching there is either something wrong with your transmission or, more likely, with the rpms at which you are shifting.

In my 5spd, I hit clutch, blip the throttle to raise rpms about 500-700 and then shift and release clutch. When done at the proper rpms it is seamless.

As for your 5th to 3rd shift, you simply don't need to floor the gas, you just need to raise rpms around 1000-1400 above rpms in 5th. I've developed my blip so it equals about 500-700 rpms and when I do a single gear downshift i blip once, when I go from 5th to 3rd, I blip twice as long.

 

Norm,

I "think" I am double clutching but might be missing the double part. To do it correctly you:
1) Push in clutch
2) Slide to Neutral
3) Release clutch
4) Blip throttle
5) Push clutch
6) Slide into desired gear

Right? What would be the difference(technically internal to the clutch and gbox) if you skipped step 3 and 5. As I have found (after reading and analysising my shifting yesterday) what I am doing.

 

You are double clutching.
But you're right, according to your numbers here is the order for "better double clutching":
1) 6) 4)
it should be called "single clutching"
no need to waste time with the clutch twice and neutral.
this way is twice as fast no matter what anyone says. not just for downshifting to slowdown, but also on a highway race (5th to 3rd). it doesn't hurt anything except for all those people's feelings you hurt out shifting them in a race.

 

that's all correct except . . .

use the brakes to slow down - that's what they are for.

 

that's all correct except . . .

use the brakes to slow down - that's what they are for.

i agree, but shifting is fun and tempting

 

Okay so you're pushing the clutch in and out twice and pausing on the way past neutral while you've got your heel on the brake and are blipping the throttle with your toe. SOOOO, all you've done is taken a perfectly good shifting/braking technique and wasted your time by throwing in a unnecessary second clutching and a pause in neutral, what's the point??? Using the 'heel n toe' method doesn't suddenly mean double clutching makes sense.

 

You are double-clutching. I'll add 7) Release clutch for the benefit of the next sentence.

The 'double' part refers to the two distinct clutch disengage/release cycles that take place.

In actuality, and as you're probably already aware, there's quite a bit of overlap among those 6 discrete steps (making the process sound and write clumsier and slower than it really is). The difference to the tranny internals is lower demands on the synchros due to matching the revs of the clutch disc and tranny input shaft. Single clutching won't rev-match those components.

Norm

 

I will concede that double clutching is nicer to the tranny, but hey, I'm single clutching. My tranny has lasted 120k miles so far. It's too much of a waste of time in normal driving, less spontaneous. I feel only a professional racer should be concerned with it.

DW

 

Sure it does, at least given a little thought to the circumstances and the physics of it. H&T is a road-race technique that there's little need for in normal (read legal) street driving, and as you approach a corner that implies much higher rpm's than normally encountered while driving on the street. The product of clutch disc momentum times rpm error is larger, which in turn becomes greater synchro demand and hence wear. Etc.

DW - In addition to professional (or amateur, for that matter) racers, anybody who downshifts such that the revs in the lower gear are more than, say, 1000 rpm above the rpm's in the gear shifted from should seriously consider it. At that point the driving is becoming less like street and more like track.

Norm

 

Ok. So double clutching will spare the tranny. After reading six pages of replies this is clear . However, I don't have a clear picture of how this works technically. I guess with time and taking tranny-101 will help me better understand.

Along the lines of sparing the tranny I have a question. When waiting at the red light which of the following will wear out the tranny if at all:

* Keeping the clutch all the way in while in neutral
* Keeping the clutch all the way in while in gear (normally 1st gear)

I've been told that wear occurs only when engaging/disengaging the clutch but not when it's all the way in regardless if it's in neutral or gear.

I humbly ask for the Forums wisdom

 

No problem. It's true that clutch disc wear occurs during engagement and disengagement. But the answer is neither of the above, because it's not the tranny or the clutch disc you need to spare when you're stopped (it's the throwout bearing).

So, tranny in neutral with clutch out. Exceptions to this exist, such as where the potential for needing to move suddenly to avoid being hit by another vehicle obviously must take priority.

Norm

 

There's plenty of use for heel-toe even in street driving (ok agressive street driving) because the simple fact of the matter is that most of us don't have enough feet to take all the steps necessary to quickly downshift going into a corner while braking and maintaining max rpms.

Unfortunately, I've found it too difficult to heel-toe on the stock pedals. So, I alternate braking with blipping the throttle for downshift and then braking again (an imperfect solution to be remedied by some pedals soon).

Double clutching in circumstances where one needs to heel-toe but can't *really* makes things more difficult.

But alas, you will have the least amount of wear on your synchros!

 

"at least given a little thought" Hey Norm give it a rest. I never disageed with you that theoretically you're right about double clutching saving wear and tear on the transmission, BUT I submit that practically it makes virtually NO difference. Geez one guy already posted that he's never double clutched and he's gone 120,000 miles with no problems. Do you have any practical evidence of just how much longer the transmission is going to last by double clutching or do you just want to continue to make people feel like, if they don't learn to double clutch, they're guuna wear their transmissions out???

"anybody who downshifts such that the revs in the lower gear are more than, say, 1000 rpm above the rpm's in the gear shifted from should seriously consider it" Give me a break. Like I mentioned earlier I did a 6-1 shift last night at 65 mph and it was no big deal. If the syncros were being excessively overloaded by such an act I know I'd be able to feel it through the shifter, and if they were REALLY being overloaded the transmission wouldn't even have gone into 1st.

I've had enough transmissions apart in my lifetime to know that they're a lot tougher than what you're saying is going to lead people to believe.

 

You, too? (Same work-around here)

I'd probably do a pedals mod myself, but I think my wife would object more strenuously than I'd care to endure.

Norm

 

Well, the only time my wife drives my car is when I have to take hers in for service!

But, I guess she might step on the wrong pedal. Hmmmm.....

Otherwise she doesn't mind the mods like y-pipe/intake/pulley/ftsb and $200 tires. It only means that she spends more money on the house! LOL.

Do you actually double-clutch in that situation, though?

 

Paul (and to whom it may concern) – Sorry I sound a little strident on this topic. What mystifies me the most is the apparent refusal-to-learn-how / refusal-to-do / why-should-I-even-bother attitude that seems to be present. It just isn't that hard to do. Now, I'm sure that when I was 18 or 20 or so I didn't double-clutch my downshifts either, but that was because nobody ever mentioned it unless/until you got tuned in to sports cars.

I'm a structural engineer by education and by profession, with some experience in fatigue-related component life. I'd also have to rate myself as an 'advanced driveway mechanic' and, yes, I've rebuilt transmissions. Even Maxima transaxles.

FWIW, synchros aren't big beefy parts like final drive gears nor are they made of anything as durable as hardened steel. They're fairly small, relatively soft and work by acting as cone brakes.

I hope I haven't given the impression that just a few single-clutch shifts, regardless of rpm difference, will result in immediate synchro failure. Or even die after a few power shifts. That's not the case. It's the accumulated damage over time, heavy damage from each of a few high load cycles being as bad as very light damage from each of a large number of cycles. It's not linear.

I can't put any numbers on anybody's specific tranny life, but one general yardstick of estimated fatigue life is expressed as a number of cycles and is related to the inverse 5th power of the stress in the parts. Synchro dimensional wear is probably not that bad, so doubling the demand on the synchro every time will probably not wear it out 32 times as fast. But a 50% increase in stress done all the time suggests (1/1.5)^5 or 13.2% of original life span, doubling the stress drops that to 3.1% of original life span. If the relation between stress and lifespan was half (or more) of life for a doubled load I might think differently. Again, FWIW.

Some more FWIW: From some Chrysler publication many years ago I remember that their then-new 4-speed manual tranny was considered stronger than most, and was tested without synchro failure over 75 power shifts. Since that was the only data point published, I have to wonder about their actual condition. Hmmmm.

Norm

 

Hey it's not like I don't know how to double clutch it's just that I really don't think it's worthwhile to bother doing and thus don't think a lot of people need to worry themselves about learning how to do it. I can shift without the clutch pretty seamlessly and yet I don't do that a lot either. Basically I just drive the car the was Nissan expects people to drive it and they sure don't mention anything about double clutching.

Funny thing is that "when I was 18 or 20" I not only knew about double clutching I was doing it all the time, but it sure had nothing to do with "sports cars", I was driving a 10 wheel tandem dump truck with two transmissions and had to be double clutching on the up-shifts as well as the down-shifts.

Figures that Chrysler would think 75 power-shifts without a failure is a good thing. I sure hope Nissan has higher standards than that because I did by first full throttle power shift when the car had less than 300 miles on it. I'm sure over the next few years I'm VERY likely to accumulate more than 75 such shifts and I sure don't expect the syncros to fail as a result.

I took a new GSXR-1100 with N2O activation at full throttle, went out and power-shifted that puppy with no problems. Man I probably put more than 75 power shifts on that bike the first day I had it at the track.

 

It's a little different situation here. For weekdays and weekend use not involving me the Max is hers and bought with that in mind. She can drive the car she has named "Cranky" (the Malibu) but greatly prefers not to. Her comment at the Philadelphia auto show last weekend regarding the new T-bird was "No stick? Then we don't want it.", so I feel pretty fortunate in that respect. Most mods aren't a problem, especially if done as an upgrade simultaneously with a repair/replacement (take note, guys) but tinkering with something as all-the-time as the driver/car interface in "her" car would be just begging for trouble. Even people as dense as I am catch on given enough time.

Norm

 

I thank you for all the information you supplied. I have been practicing the double clutch more often, and no I have not seen The Fast and the Furious. If I can save some tranny life after numerous dumps from fifth to third I gotta.

 

Me either. And thanks.

Norm

 

In single cluthing mode I
a) Push the clutch
b)downshift from 3 to 2
c) blip the throttle so i wind up at an engine speed higher than my previous gear
d) let out the clutch

Using this method, when the cluth engages, engine and tranny is spinning, more or less at the same speed. Therefore I would think that the single clutch method would also save the synchros. No?

How would double clutching be better for the synchros than what I just described above?

DW

 

When the clutch is disengaged the engine cannot speed up the clutch disc or the tranny input shaft. The whole point of having a clutch is to disconnect engine power from the tranny so you can shift easily. However, this means that everything "downstream" of the clutch friction surfaces cannot get "blipped" with the clutch disc (on the downstream side of the clutch assembly) and flywheel/pressure plate (the upstream side) surfaces separated.

I'm not disagreeing with the value of a single-clutch-with-a-blip. I will freely agree that blipping as you single-clutch on a downshift is much better than doing nothing. And I'll even concede that the single-clutch-with-blip method represents a bigger reduction in wear over the no-blip than a double-clutch does over the single-clutch-with-blip, since the larger amount of potentially "wrong-speed" mass is in the flywheel, pressure plate, and crank, i.e. on the upstream side.

Maybe this whole thing is a function of mind-set, similar to not wanting to settle for a lower score on an exam when you could have pulled a 98, or of not being satisfied with a 15.9 et when quicker was within easy reach.

Norm

 

This has been a very interesting thread. We may not double shift because we are lazy but I think we understand the advantage and the reason for doing it.

Threads like this are the reason that I'm still a member of this forum. It is very rare on here anymore that a thread doesn't degenerate into a "post *****" or smiley contest.

 

i second that statement!!!