Double De-Clutching

My mum today asked me if I "Double De-Clutched" when I shifted down gears (eg. 4-3, 3-2). I'd no idea what that meant, having used automatics most of my life. But after some searches, I found some videos which show it being (please do call me wrong if I am) increasing the engine RPM during the neutral change during a gear change, to match the equal value of a new gear when shifting into that gear. Is that right? I've never known it - if I shift down a gear, it's usually do it to slow me down before a junction or roundabout, so I actually want the additional engine braking that pulls me back. Otherwise, if I'm coming up on a red light or other "stop" point, i'm quite happy at 60 mph to put the clutch in, and just coast/wheel brake until I stop. In fact, I could sometimes just coast with the clutch in for half a mile or longer while traffic is gradually slowing down to a junction.

What is the actual use of this "double de-clutch"?

(edited 8 years ago)

Reply 1

CurlyBen

It's not necessary on cars with modern gearboxes. When shifting the input and output speeds have to be synchronised and in simple gearboxes that's achieved by double declutching, but in virtually any car gearbox built in the last 40 years or so a synchromesh unit achieves the same effect. Double declutching is virtually redundant now, although it's still used sometimes in racing or for some specialised applications.

Reply 2

cole-slaw

What are you driving, an articulated lorry?

Double de-clutching is unnecessary and considered bad driving nowadays, as is heel and toe and left foot braking. Brakes to slow, gears to go.

Reply 3

FXX

The modern equivalent is blipping the throttle before engaging the clutch when downshifting. This way you're not relying on the slip of the clutch plates to bring the engine speed back up. Makes for a much smoother gear change and good fun if you have a decent sounding car.

Reply 4

spotify95

Original post by CurlyBen

I can second you on that. I don't drive yet (I'm hoping to in the next few years) but I do know a bit about car gearboxes. The only car I know of that required a "double de-clutch" was a 1963 spec car, and that was only when going down into 1st gear. You have to go back into the 1940's to find vehicles that required double de-clutch on all of the gears.

So yeah, unless you happen to drive a vehicle (or need to drive a vehicle) that is about 50 years old, double de-clutching is not necessary.

Original post by cole-slaw

What are you driving, an articulated lorry?Double de-clutching is unnecessary and considered bad driving nowadays, as is heel and toe and left foot braking. Brakes to slow, gears to go.

It's unnecessary unless you have an ancient vehicle (see above). Though I doubt most students will be going around in 1960's spec vehicles! :tongue:

(edited 8 years ago)

Reply 5

dhr90

Might not be necessary, but it can be fun!

Reply 6

Minardi

Helpful in one of our old tractors on the road, the syncro isn't brilliant on it so a double de clutch helps no end! In anything modern and car shaped it shouldn't ever be needed.

Original post by cole-slaw

What are you driving, an articulated lorry?

Double de-clutching is unnecessary and considered bad driving nowadays, as is heel and toe and left foot braking. Brakes to slow, gears to go.

As to the comment on engine braking - I know that's the way it's taught now (and was when I learnt), but it doesn't mean I agree with it (not aimed personally at you, aimed at the idea in general). I lack the mental dexterity to explain myself, suffice to say I think it's an essential skill, particularly if you are driving a full loaded car or on trickier surfaces. Dropping down a couple of gears on a slippery incline will descend you in a slower, controlled manner. Dipping the clutch and hitting the brakes is much less controlled, particularly if you are the sort who stabs the brakes. Anything heavier than a car often comes with a special pedal to give increased engine braking, they are even fitting tractors with it now, I read somewhere the system offers a 40% increase in braking performance.

Heel and Toe? There's a time and a place for it. Left foot braking? I do it when I drive an auto. I've left foot braked for years on two pedal ag kit, it's completely natural to me.

Reply 7

cole-slaw

Original post by Minardi

Helpful in one of our old tractors on the road, the syncro isn't brilliant on it so a double de clutch helps no end! In anything modern and car shaped it shouldn't ever be needed.

As to the comment on engine braking - I know that's the way it's taught now (and was when I learnt), but it doesn't mean I agree with it (not aimed personally at you, aimed at the idea in general). I lack the mental dexterity to explain myself, suffice to say I think it's an essential skill, particularly if you are driving a full loaded car or on trickier surfaces. Dropping down a couple of gears on a slippery incline will descend you in a slower, controlled manner. Dipping the clutch and hitting the brakes is much less controlled, particularly if you are the sort who stabs the brakes. Anything heavier than a car often comes with a special pedal to give increased engine braking, they are even fitting tractors with it now, I read somewhere the system offers a 40% increase in braking performance.

Heel and Toe? There's a time and a place for it. Left foot braking? I do it when I drive an auto. I've left foot braked for years on two pedal ag kit, it's completely natural to me.

Why are you slowing down on an incline anyway? you should be in an appropriate low gear before beginning the descent. If you need to engine brake, you've hit the slope going too fast.

heel and toe is incompetence, pure and simple. just time your gear change correctly.

Reply 8

scriberg

only lorry drivers are taught how to double clutch, its just an old technique which is used for rev matching

Reply 9

CurlyBen

Original post by cole-slaw

On an incline you need to use braking (of the service and/or engine varieties) to keep your speed down. It's not such an issue in a car, but just relying on service brakes with a large, heavily laden vehicle on a long hill can lead to boiled brakes which isn't much fun. Some trucks (particularly in the US) enhance the engine braking with jake brakes/compression brakes.

As for heel and toe, I suspect you don't know what it is - it's a performance driving technique, it's certainly nothing to do with incompetence.

Reply 10

Nuffles

Original post by cole-slaw

....

Someone's got a bee in their butt.

I have an HGV license and occasionally drive HGVs. HGVs often have a fourth pedal which changes the exhaust timing, increasing the 'drag' on the engine and thus inducing more engine braking. Very useful for long descents to control your speed, seeing as you have 30-40 ton behind you.

Left foot braking is absolutely fine. I can't say I do it much personally, but if you like putting your foot down a bit or you go to some track days then it certainly has its benefits, especially on turbo cars it allows you to keep the turbo spooled. It's also useful if your car is stuck on mud or ice and you don't have traction control.

I double declutch quite a bit. The synchro on third in my car is a bit worn out (I need to get around to changing the gearbox oil, actually) and I do it on the work van because again the gearbox is pretty shagged and it appreciates it - it slips into gear so much more easily when double clutched.

(edited 8 years ago)

Reply 11

Alfissti

I doubt there are very many HGVs that require double-clutching either these days. Most of the newer ones are automatics and that is certainly the case with those used by most well known hauliers.

Reply 12

Minardi

Original post by Alfissti

I doubt there are very many HGVs that require double-clutching either these days. Most of the newer ones are automatics and that is certainly the case with those used by most well known hauliers.

Very true, although alot of drivers I see don't like them that much. They make maneuvering on slippy farm yards very difficult.

Reply 13

sailorben

Double declutch is just unnecessary on modern cars, I do rev match on downshifts though. Not really necessary, but I like the throttle blip and the smoothness, without having to worry about gradually releasing the clutch.
Also allows me to downshift when I wouldn't if I didn't rev match, to use the engine breaking. No point using brakes if I don't have to... save them for the country road seshs.

Reply 14

CurlyBen

Original post by Nuffles

I have an HGV license and occasionally drive HGVs. HGVs often have a fourth pedal which changes the exhaust timing, increasing the 'drag' on the engine and thus inducing more engine braking. Very useful for long descents to control your speed, seeing as you have 30-40 ton behind you.

Which licence do you have, C+E? I thought about doing it after I'd spent a summer onion carting (20 ton, 30' trailers) but never quite got round to it. Did you get it whilst you were working somewhere or just decided it would be useful to have?

Reply 15

JC.

The last thing I owned that neccesitated double declutching was a '56 land rover series 2 that only had synchro in 3rd and top.
No point in doing it doing this in something with a modern 'box unless the gearbox itself is knackered and you're trying to nurse it on a bit longer.

Unless your car looks a bit like this one of mine, chances are it's something you'll never need to worry about. :wink:

Reply 16

Nuffles

Original post by CurlyBen

Just C/Class 2. I decided it'd be useful to have, although I'll probably go back and do the C+E at some point too. I just need to get the CPC training sorted out now. Sigh. I currently drive a 3.5t box van for a living but looking at moving on up in the world and just got a couple of calls about jobs involving 7.5t+ trucks, which means I need to get my tacho card sorted too as it got nicked when my wallet did a month or so ago.

(edited 8 years ago)

Reply 17

Minardi

Original post by Nuffles

I still need to do my B+E! Dad still does all the Land Rover and Trailer work! I will probably do my C1 in time aswell, will be handy to have. I'd like to do full C+E, but it's a dear game and I have no immediate need for it.

Reply 18

KCLeblanc

Original post by Minardi

I will probably do my C1 in time aswell, will be handy to have. I'd like to do full C+E, but it's a dear game and I have no immediate need for it.

I would try to do C instead of C1. It's literally all the same process for both licences, the only difference is the vehicle you will be taking your test in. C1 will most likely be a 5.5 tonne Transit/Sprinter while C will be an 18t lorry.

Doing C1 only really makes sense if you only ever want to drive 7.5 tonners.

Reply 19

Nuffles

Original post by KCLeblanc

I'm fairly sure he meant C1 as in Class 1, i.e. the old C+E (full artic) and C2 meaning Class 2, i.e. the old C license. I did my Class 2 in this bad boy:

Original post by Minardi

Yeah B+E is the next one as it's fairly cheap and much more useful than a full C+E/Class 1 to me at the moment, and then probably a forklift license too as half the rigids on the roads these days seem to have a forklift hanging off the back of them.