Double clutching, blip once or twice?

[k76]

I'm struggling with moving from single clutch heel/toe downshifts to double clutch downshifts. I can do the single clutch version just fine, but when I double clutch I just can't get that nice smooth feeling when you release the clutch. I don't have the best coordination in the world, and this really is torture for my long legs. But I think I'm doing something wrong.

It's either:

clutch in - move shifter to neutral - clutch out - blip throttle - clutch in - engage gear - clutch out
When I do this I can engage the gear nicely, but the revs have dropped by the time I do the final declutch, and the car jerks abit.

I've also tried
clutch in - move shifter to neutral - clutch out - blip throttle - clutch in - engage gear - blip throttle - clutch out
which is better in theory, but I struggle to get my legs to do it properly. The last blip needs to be a very quick half blip, I tend to overdo it and the car lunges forward instead.


Any hints?


Kris

[Luke]

Personally, I never found two blips to be necessary. Maybe you could just try giving the throttle a sharper, longer stab?

[Davidm1600]

Hi Kris

To the best of my knowledge and from my experience, your first description is the correct method.  I am not sure I can think of any benefit of the second blip on the throttle as you describe.  You can actually do the double declutch going down or up through the gears.  This is typical of race cars from the past which had no synchro and most truck drivers used to double declutch going up through the gears.

To be truthful, for modern cars I actually don't think that there is a lot or no need to do it, but comming from an old car mentality, I still do it with my '03 156 JTS as much as I would with my '69 1750 GTV.

From my experience, there is only two ways to learn the method. By practice, and accept at first it may seem strange, or through necessity, have a gearbox with failing synchros (ie. like my GTV) or a car with no synchromesh (old pommie cars for one), and in that case you will most definitely learn to do it correctly.  It is all about trying to match engine revs with the cars speed, and yes if you are not quick enough the revs will drop. I got to the stage where I could actually change gears without use of the clutch and not crunching gears.  (Mind you I practised this on a crappy old/rusted out work Ford Escort van), and basically couldnt care less if it suffered a little.

If you do get it right it should be an automatic thing and not require any thinking to do it.  Keep practising mate !!

[Simon Aarons]

I agree, i have never blipped the throttle twice while downshifting, in-fact i have never had the need to double clutch while downshifting.

I don't find it necessary, even on the race track and by no means does my car have a great gearbox. I have found going from 3rd to 2nd is done very smoothly by just single clutching and matching the revs. Though i was probably only traveling at 60-65k's through the corner, any faster and its better to stay in 3rd!

[k76]

Thanks all,

I think I got myself confused with the second blip, trying too hard to match the revs perfectly when engaging the gear. I too learned to do clutchless shifts with my first car, a very high milage corolla. Apply very light pressure on the stick, blip the throttle and you can feel on the stick when the revs are matched and it almost just falls into gear.

When I think about it I probably need to shift abit faster, and work on timing my blip better. It keeps my commute interesting. I've been using my wife's Yaris recently, blippping the throttle is about the most exciting thing I can do with that car...

Kris

[Mat Francis]

+1 for a single blip. My first impression is that it is probably just a confidence issue, i went through the same thing whilst learning it. I found it a scary thing to do, but when you get the revs right (or really bloody close) you should be able to let the clutch out as fast as your leg can move (smoothly of course), meaning the revs don't have time to drop off to much as you describe. It took me at least 18 months for this to be second nature in the Alfetta. I can't get anywhere close in the 75. Keep practising!

Heh, and on a side note, nothing beats clutch less shifts for shits and giggles. Jimmy and i once got his beamer from frankston to ringwood without using the clutch (with the exception of traffic lights of course). The best bit? he was driving, i was on the gears 

[Jekyll and Hyde]

Personally, I never found two blips to be necessary. Maybe you could just try giving the throttle a sharper, longer stab?

What he said.  Need a bit bigger rev!  Incidentally, you can practice this without needing the brake pedal if you want (for example coasting up to a set of lights, going uphill), which can help getting the 'feel' right.  And as mat said, you can dump the clutch in at full speed when done right...

[Tim Jobson]

Hi Guys,

What is the advantage or disadvantage of :

Clutch in - blip accelerator to bring revs up while moving shift lever to lower gear - Clutch out   ?

Tim

[Davidm1600]

Tim, as mentioned in modern cars with excellent synchos - nil.  It is a technique largely that originated in cars from the past when they had either no synchros or poor synchos and it helped make for smooth gear changes while maintaining revs and therefore speed.  This applied very much to racing in old cars.

[Tim Jobson]

I suppose my question was more to do with what technique is  better for the gearbox syncros,

Clutch in - blip accelerator to bring revs up while moving shift lever to lower gear - Clutch out   

or

clutch in - move shifter to neutral - clutch out - blip throttle - clutch in - engage gear - clutch out

I have always used the first technique to keep the car more stable when changing down, is it not as good as the second method to help wear on syncros???

Tim

[Davidm1600]

Tim, sorry mate I misunderstood your question  Ok While I am not a mechanic and perhaps someone with better knowledge may wish to provide more definitive/technically correct advice, my guess is that to an extent it probably doesnt matter which method one uses, as per your description.  The key being to try to match the engine revs to speed to put less stress on the sychos in the box.

As we all know, Alfa 2nd gear synchros in 105s and 116s are notoriously weak.  Hence if one can master the correct technique this will give some level of protection from undue wear.

From my experience, and advice heard from other Alfa owners a part of the problem lays in driving off in the first instance with cold oil.  Not allowing the car to warm up.  Typically when using the car first thing in a day, baulking between the gears is not uncommon, (due to cold/thick oil) etc.  Hence the other trick also is to run up through the gears before heading off.

Now if this is so for the older models I am not sure why this might not equally be so for modern cars, suffice to say that perhaps the design of modern synchos, gearboxes is better and inherently less subject to synchro failure.

As to the two techniques you describe, I am pretty certain the second method you describe is technically the correct way to double declutch.  Dave

[AndrewO]

Hi Tim,

Hopefully someone will correct me if I get this wrong.

The first method has the clutch disengaged all the time so all you are doing is matching the engine to the drive shaft.  It makes for smoother changes because the clutch has far less work to do (both sides spinning at the same speed). 

The second method (full double de-clutching) has the clutch engage half way through to fully engage the gearbox so the synchros (input shaft and output shaft) are at the same speed so there is no load there when you swap cogs, and after that (the double part) you engage the clutch with it doing less work with the engine and driveshaft at the same speed.

The first method works well and is good for 90% of use because it also helps the synchros a little bit by the way the input and output shafts are connected (don't ask me how).  The second is ideal for long life, or if you have a real problem with your gearbox.

[Colin Byrne]

there is already a good thread on this, but
1st method- will do nothing for your synchro, by dis-engauging the clutch you have seperated the engine from the gerbox, so nothing you do to the engine is going to effect the gearbox.  it will however reduce the likelyhood of compression lock.
2nd method- when done corectly will match gbox input and output shafts and significantly reduce sgnchro wear

[shane wescott]

It's always been one blip for me. Luckily for me the first car I bought (while on Learners) was a '71 1750 Berlina.

Any resemblence to a 2nd gear sychro was purely coincidental and never intended by the manufacturer :-)

So I had to learn double clutch fast. It's all about practice, and a short sharp jab on the throttle is required.

IMHO Part of DBL clutching is gearbox maintenance, and part is listening to the engine rev :-)

Catch ya

Shane

[WilliamB1750]

  This is typical of race cars from the past which had no synchro and most truck drivers used to double declutch going up through the gears.
Keep practising mate !!

And we still do in modern trucks, because a number of them still use unsychronised gearboxes. I just had a quick look through you tube etc to see if I could find a nice video, this one was the closest I could find   http://www.youtube.com/watch?v=JliPGde8jMM&NR=1  and you will notice that he doesn't actually double clutch when changing down.

2nd method- when done corectly will match gbox input and output shafts and significantly reduce sgnchro wear

And that is the point of double clutching, reducing synchro wear is a benificial by product, but to have the engine in the correct gear and at the correct revs for the corner.
This is how it works in the truck  http://www.youtube.com/watch?v=YfsyZQAjKvM&feature=PlayList&p=B7BBB1E177928594&playnext=1&playnext_from=PL&index=15  Listen to the revs