double clutching

[lj]

i know some of you guys will think this is a stupid question but im new to driving. my parents have a hj75 troopy.

i was just wondering what the purpose of double clutching is and when/how to do it properly

thanks

[PRZOOK]

When downshifting from 4th gear to 2nd at 80 kph, you need to raise the engine speed from 2200 rpm to 5000. To prevent excessive synchroniser wear, the clutch is depressed and the shifter is moved to neutral. The clutch is then released, and the accelarator is depressed to bring the engine speed up to where it needs to be for the lower gear. The clutch is then depressed again and the shift lever moved into the lower gear. When the clutch is released the second time, the engine is already turning the proper speed.

There ya go. it is to prevent excessive synchroniser wear.

[twinnie]

on the earlyer models it was used to get into 2nd and 1st at any speed but with new cars (1980 onwards) it's not usaly needed exept for stopping wear but as a learner driver just concentrate on driving normaly testers don't like fancy stuff like double clutching. i'm only on my p's still so i know and a few of my mates found out the hard way.

Matt

[Evan]

With modern synco gearboxes its really not needed.
When downshifting to a low gear from a high speed its useful to make the shift smoother and prevent some wear but not essential.

Of course going into first gear on just about any nissan gearbox i find you need to double clutch and match revs, where as on toyota boxes dont seem to need to do it.
Could be just the cars i have driven but its been the same on a fair number of nissans and toyotas i have driven.

[lj]

thanks for the help guys

[bru21]

instead of double clutching, i like to do a bit of double fletching

[Heathx4]

When downshifting from 4th gear to 2nd at 80 kph, you need to raise the engine speed from 2200 rpm to 5000. To prevent excessive synchroniser wear, the clutch is depressed and the shifter is moved to neutral. The clutch is then released, and the accelarator is depressed to bring the engine speed up to where it needs to be for the lower gear. The clutch is then depressed again and the shift lever moved into the lower gear. When the clutch is released the second time, the engine is already turning the proper speed.

Just to nit pick, you're actually bringing the gearbox speed up by double clutching aren't you? You could bring the engine up without releasing the clutch of course. Releasing the clutch in neutral and giving the acc a tap gets the input gears of the gear box spinning so they match approx with the output gears. Is that right?

[N*A*M]

double clutching is for trucks. there are a lot of misunderstood opinions on this. just search the net for double clutching and laugh at all the stupid responses.

rev matching on the downshift is what we're talking about here. even so, it's not essential unless you are racing and need to be in gear and in the power band on exiting a corner. and that's using heel+toe and you go straight to the low gear (you don't wait in neutral). don't worry about it if you are learning to drive stick. just be smooth with the clutch and pick the right gear for your speed.

[Shadow]

it was also for old dog boxed trucks where you had to double clutch on every shift (up and down). but the modern synchro gearbox has resolved this need....

[Daisy]

double clutching is for trucks. there are a lot of misunderstood opinions on this. just search the net for double clutching and laugh at all the stupid responses.

rev matching on the downshift is what we're talking about here. even so, it's not essential unless you are racing and need to be in gear and in the power band on exiting a corner. and that's using heel+toe and you go straight to the low gear (you don't wait in neutral). don't worry about it if you are learning to drive stick. just be smooth with the clutch and pick the right gear for your speed.

Agreed with NAM on this. I drive a heavy truck and i know this so....

[-Nemesis-]

What's the go with the neutral part>? I always heel + toe when i'm getting into it in my XR8 but don't use neutral. What's the point of N? Or is it easier for some people?

[stumped]

What's the go with the neutral part>? I always heel + toe when i'm getting into it in my XR8 but don't use neutral. What's the point of N? Or is it easier for some people?

always wondered what the deal was with taking the clutch out again, never actually bothered with that when rev-matching as nam calls it....

... is the neutral thing a truck thing... to do with gearbox speed??

[Heathx4]

Ha, how a seemingly simple question can turn tricky. As most people have realised, there must be more to it than the rev-matching exercise used in the heel-toe method for example. That can be a useful technique, mostly in racing, or as I use it, to stop wear on the clutch and for smoother deceleration via the gears. That is, when I drop down a gear to reduce speed, I might give the acc a tap as I'm going from 4-3 or 3-2 so when I release the clutch the engine doesn't have to spool back up via the clutch. You get slightly less engine braking, but it is smoother and doesn't load the clutch as much.

I have always thought of double clutching as a gearbox speed matching thing (hence the need for clutch out in N) as I described earlier. But on second thoughts, the gearbox speed is going to drop fairly dramatically once you release the clutch again isn't it? Can someone tell me what is left spinning and what will be stopped in short time when you push the clutch in? Perhaps instead, double clutching is simply to line up the gears for the next engagement - much as you might do when the reverse gear wont slot in - just release the clutch in neutral, give the acc a kick, and try again.

[Ando_13]

Double clutching is for trucks, not needed in lighter vehicles (cars and 4bies). If your 4bies needs it, I be getting your gearbox checked!

[Wendle]

the work truck i have been using to drag my buggy around on needs to be double clutched, and it is a pain in the arse! why you would do it voluntarily on a vehicle that didn't need it is beyond me?

[Fieldsy]

the work truck i have been using to drag my buggy around on needs to be double clutched, and it is a pain in the arse! why you would do it voluntarily on a vehicle that didn't need it is beyond me?

I agree I have spent quite a bit of time in 5 speed macks with crash box's and get sick to death with double clutching. I would say 99% of trucks on the road today don't even need to be double clutched.

but I tell you what when you drive something without syncros it makes you realize that to get double clutching to work you have to have the rev's spot on, so much so that when you have it just right you can even get away without useing the clutch. ie upchange; get the rev's up in gear, back off, gearleaver into neutral, hold while rev's drop, notch into next gear. or down; let rev's drop in gear, gear lever into neutral, rev in neutral, slip into lower gear. mind you all this is bad for the box, clutch, whole bloody driveline,

Then you have Dino chaingeing but let's save that for another thread

[mkpatrol]

[quote="PRZOOK"]When downshifting from 4th gear to 2nd at 80 kph




Why would you want to do that? Doing that would definately wear your synchros.
Double clutching is only for vehicles with no synchros in the gearboxes. Waste of time otherwise.

[Tojo]

its usefull if your clutch fails. As Fieldsy said you can change gears without using the clutch.

[bad_religion_au]

you guys use the clutch to shift gears??? i only use it to go back to 1st and to take off from the lights (long story short, ran my 40 for a year on a shitty clutch master)

rev in gear, back off slightly and smoothly slip it into neutral, match engine revs, into next gear.

after time you don't usually have to stop in neutral you match shift speed to engine dropoff...

[Bazz107]

HI,

I belive that you should know how to change gears without a clutch, have had expensive tow trips saved by the fact that i can change gears without a clutch all together. Mate of mine had Slave cylinder on hilux die, 200 clicks from nearst town, Drove the lux into town got rebuild for 100 dollars much better than the several that it would have cost for towing and the time wasted trying to get towed. But should not be used for every day driving.

Byron

[bad_religion_au]

actually clutchless shifting done right will cause no ill effects. if you force it out of gear, instead of backing off slightly to assist it, or force it in gear instead of spot on matching your revs, it does damage, but if you perform these tasks properly, there is no drama, actually can be healthier than shifting back from 4-3 say, and making the engine match road speed by just dumping the clutch.

[mkpatrol]

its usefull if your clutch fails. As Fieldsy said you can change gears without using the clutch.

Bwahahahah, do you realise what you just said. Whats the point in double clutching if its buggered.
Thats gold

[berazafi]

If the cluch isnt depressed the syncros wont spool up, the gear will either crunch or go in, forget learning to double clucth just learn to drive without a cluch it would be far more useful

[Dozoor]

don,t want to go into this But , Some boxs like it some don,t
The basis of double clutching as stated by a few people was in early non synchro boxs mainly trucks , if where talking trucks -- you are in second your mainshaft and cluster gear are turning at 2000 rpm ,
you need first to slow you down , the jump from first to second in most old trucks is substantial , 3.8 maybe down to around the 7-1 mark
your engine will need to double its revs , place your clutch in to grab neut let your clutch back out to increase gear speed , (in these sorts of vehicle it was not uncommon to just drop your foot on the throttle until you heard the valves float , or bounce as people call it , while the clutch is out this increases your main and cluster speed to a more apropriate
match , clutch goes in agian and you slip[ it into first ---

Its really just driving without a clutch

If you are driving a heavy vehicle you should learn how to match engine ,gear, road speed -

Some boxs like the RRangers and others have a clutch brake as well,
For instance when you pull up at the lights and go to grab a low gear
All you may get is a huge cruntch on one of these , If you depress the clutch hard agianst the floor this activates the clutch brake stopping the still spinning gear trian .If its adjusted right offcourse

Just some thoughts ,
Larry.