BXProject

[David]

Ah, still, to this day, i can't much see the point of double de clutching. Surely its quickest not to use the clutch at all?

You've never driven something with a complete crash gearbox have you? Unless you get the revs absolutely spot on (IE to within about 10 rpm of each other) you will shag the synchro rings and/or bugger the selector clutches by clutchless changing, and to get that ~10rpm accuracy is a slowish process.

On a good car gearbox, double-de-clutching doesn't really make things much faster, but on something with a much heavier gearbox, it allows you to change gear significantly faster, and generally much smoother.

[docchevron132]

/\ what he said.
When you first start driving crash boxes (especially commercial stuff) it's really difficult to get right everytime.
Once you get used to it, the change is very fast and slick.
The other thing to bear in mind, again especially with commercial stuff, is that the engine takes a long time to die down, if you dont have the clutch depressed, by the time the engine revs have fallen enough to match the next gear up, invariably the bloody thing has stopped!

[Philhod]

been there, done that

Funnyly enuff I never lost it with the AEC horizontal engines, they seemed to slow down a lot quicker than say, a Crossley big straight six. I'm sure the fuel kept dribbling in after you had taken your foot off completely, with those. It was the same when you switched it off,I know it didn't but it seemed to run on for about 2 minutes

[Bx Bandit]

But not using the clutch at all still requires the engine revs to synch with the gear being selected no? At least, when I've tried not using the clutch the bugger won't go in gear until the revs fall (changing up). Or, to put it another way, by not using the clutch AND getting a quicker gear change must knacker the gears/synchros????

So crash boxes and larger vehicles aside, surely the quickest way to change gear in a car (without fucking the gears/synchros) is as per the standard method?

[David]

So crash boxes and larger vehicles aside, surely the quickest way to change gear in a car (without fucking the gears/synchros) is as per the standard method?

Double-De-Clutching effectively achieves what a synchro does, but using engine power, so by DDC'ing a car gearbox, you remove 90+% of the wear on the synchro, or do the job of the synchro if it's fooked.

[Vanny]

I'm sure the fuel kept dribbling in after you had taken your foot off completely, with those. It was the same when you switched it off,I know it didn't but it seemed to run on for about 2 minutes

Erm, if the fuel didn't keep dribbling in, wouldn't the fucker stall?

[docchevron132]

you're missing the point Vanny.
Whe you consider the Anti-Stall on big fuck off diesels can make a difference between returning to idle in 3 seconds or 3 minutes (I'm not joking) then if they are the slightest whack out it fucks things up a treat.
Add to that a flywheel that weighs as much as a house (ok, slight exageration) etc and seriousley, they can run on for a day and a half if anything other than base fuelling is passing the injector tips.

[Vanny]

nope Docco, i'm not missing the point, just didnt have all the answers so asked the question!

On the DDC, it seems your all showing me what i thought, it's a pointless antiquated task, used only on old stuff that clunks, so for your average joe theres no point. AIM still bang on about it, like many other things they haven't updated in for ever. On the flip side, i often dont bother with the clutch when changing (up?) in the Focus, its pretty easy to swap without it, can't do that in the Corsa or the valver mind.

[David]

On the DDC, it seems your all showing me what i thought, it's a pointless antiquated task

If you understand the concept of DDC, then your can make your gearchanges silky smooth, and not generate the "shunt" that 99% of drivers seem to manage as you bring the clutch up in the next gear.

It's more a case of it doesn't get used these days because modern gearboxes don't demand it. However, just because you can "get away" without DDC, doesn't mean it's not a good skill to have.

[Bx Bandit]

Well, as Vanny say's, DDC is virtually a redundant operation in a modern car when the snchro's are ok. And I hadn't thought of Davids point that if you DDC coreectly, then you can reduce/eliminate wear on synchro's and DDC of course would come in handy on my box with fooked synchro's on 3rd & 4th. Not strictly necessary as it will change gear so long as you take your time and a good DDC'er may do it quicker.
As far as the shunt that David mentions, I put that down to being lazy (and I don't mean you're lazy David!). It's easy just to take time and let the clutch out slowly. In fact, when I went round the Castle Coombe circuit in a Formula Ford, I got full marks for smooth gear change (I shan't mention the rest of the scores! )

[Philhod]

I'll be honest, I haven't ddc'd for ages, but since this discussion I've been doing it all the time
I'm now back to expert standard, making fast smooth changes and like David says, saves wear on the synchro's. It would render your box smooth Bandit were you to get a bit good

[docchevron132]

Not strictly necessary as it will change gear so long as you take your time and a good DDC'er may do it quicker.

Erm, have tried ditching the gear oil and using 15/40?


I dont tend to DDC on upshifts since I got used to "the point" at which its all in synchronisation and just slip the stick in (missus), I rarely DDC on upshifts in crash boxes these days, just waight a bit, but usually DDC on downshifts, especially in the valver since the diff has more backlash than I'd like really.
That said unless you're giving it beans in the TD it's a bastard to DDC in, duno why, it just is.

[Vanny]

stiffer clutch?

[docchevron132]

Nah, they're both exactley the same, vite point too, they have to be so I can drive them.
It's more to do with the revs I think,
The TD is easier to DDC in if you run it up to about 2.5K +. But since I rarely use that many revs then it's an issue.
I can go for weeks without going past 2.2K revs. Low revs and very tall gearing thats widely spaced seems to not work for DDCing in it..

[Bx Bandit]

Not strictly necessary as it will change gear so long as you take your time and a good DDC'er may do it quicker.

Erm, have tried ditching the gear oil and using 15/40?


I dont tend to DDC on upshifts since I got used to "the point" at which its all in synchronisation and just slip the stick in (missus), I rarely DDC on upshifts in crash boxes these days, just waight a bit, but usually DDC on downshifts, especially in the valver since the diff has more backlash than I'd like really.
That said unless you're giving it beans in the TD it's a bastard to DDC in, duno why, it just is.

I changed the oil two years ago mate. I think there is some sort of additive in the box though as the oil doesn't come out clear, it's various shades of brown/beige. Reverse always crunches too, long after the TD box would.
What's 15/40 dude?

[Philhod]

Err I think he means viscosity dude. Or is it viscosite in French?

The Picasso box ddc's very well, but than it never crunches anyway.

With the BX normal changes have to be precise, if you mistime anything it crunches

Perhaps that's why it doesn't ddc too well???

[jonathan_dyane]

It's odd, but of all the BE1/3 cars I have driven, BX's have had the most variable of gear change quality. My father had a 91 diesel which had a terribly stiff and unpleasant gearchange which was not linkage related, however in the 40 000 or so miles he had it it never got any worse. My old TZD had a particularly notchy and slow change, but again never deteriorated while I had the car. Thankfully the change in my current BX is as good as it gets for a BE.

Comments?

PS, the Doc's reference to 15/40 is to use normal 15/40 engine oil in your gearbox, which apparently is what was originally specified when the BE1 came out, and gives for a better change. Haven't tried it yet, but will be when my BX goes back together!