Myles Posted April 28, 2005 Share Posted April 28, 2005 In my tintop (Focus), I am now in the habit of double-declutching where possible. Now, that's all well-and-good, but my question is about the behaviour of the gearbox when I stop the car and pop it into reverse... In some cars I've driven (old Cavs IIRC), the handbook recommends pausing before changing into reverse - and in reality, if you didn't, then you could struggle to select reverse - irrespective of any nasty graunching sounds... Anyway, I had been under the impression that a double-declutch into R should be beneficial - to give the various shafts etc. a chance to slow-down/stop/whatever - but in actual fact, I can always feel a slight graunch as the gear slots in - whereas a single-declutch (although notchy) seems fine... So what's going on, Alfie? Is it a case that the double-declutch is allowing some of the gears to sort themselves out - allowing a faster initial change which is then met by the stubborn reverse cogs??? ps - *no* I don't blip the throttle going into reverse... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Joe 90 Posted April 28, 2005 Share Posted April 28, 2005 Some/many/most (I'm not up to speed any more) cars don't have syncro on reverse, others do. I think the japs were first to introduce it, and it might have become more common. Adding syncro to reverse increases the gearbox losses, so there are good reasons for keeping the old 'crash' arragement. SEP field working, not spotted in 103,300 miles. Some photos on webshots, updated 25 Jan Link to comment Share on other sites More sharing options...
Myles Posted April 28, 2005 Author Share Posted April 28, 2005 Yes - but (especially) if the box has no reverse synchro, shouldn't double-declutching make the change smoother rather than worse? Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Sheds Moderator Posted April 28, 2005 Share Posted April 28, 2005 If you have no reverse synchro then I think a pause is better than DD. DD will still allow the input shaft to turn at engine speed, say 800 rpm. The shaft may not have time to stop before you engage the gears. Pausing OTOH will allow the input shaft to be disengaged from the engine and stop of its own accord. DD is only beneficial when everything is turning in the same direction IMO. Obviously the introduction of a reverse idler gear throws this out. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted April 28, 2005 Share Posted April 28, 2005 DDC will do nothing for you when slotting first or reverse at standstill. The whole point of DDC is to use the engine to spin up the input shaft to the same speed it will be running at after the gear has been engaged. When at standstill, the output shaft is stationary, so the matching speed for the input shaft is... zero. So what you need is to let everything settle down having come to rest and disengaged the clutch - hence the pause. If you have clutch drag you will always get a graunch. Link to comment Share on other sites More sharing options...
Myles Posted April 28, 2005 Author Share Posted April 28, 2005 Right. That clears it up Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
vikebo Posted April 28, 2005 Share Posted April 28, 2005 Interesting, anyone know how you pop into reverse when driving like this then? http://www.koreus.com/files/200411/maitrise.html Just curious... Eivind Link to comment Share on other sites More sharing options...
Joe 90 Posted April 28, 2005 Share Posted April 28, 2005 A trick learnt on knackered old MGs is to stick it into first whilst stationary before going into reverse. This counteracts clutch drag so that the reverse cogs are all stopped. SEP field working, not spotted in 103,300 miles. Some photos on webshots, updated 25 Jan Link to comment Share on other sites More sharing options...
susser Posted April 28, 2005 Share Posted April 28, 2005 Oliver's got it right. Selecting first stops the input shaft using the First gear synchro, then it slips into reverse easily. However,,if you really like "double clutching instead of granny clutching" as some twat said on 2 fast 2 furious. (another story altogether !!)you can. Like this;Stop engine, engage clutch, declutch, start engine, engage reverse. QED. 😳 Link to comment Share on other sites More sharing options...
andy couchman Posted April 28, 2005 Share Posted April 28, 2005 Spose the other reason to double declutch is when going from first reverse to second reverse. What, some of you only have one reverse gear? 😬 Andy Link to comment Share on other sites More sharing options...
susser Posted April 29, 2005 Share Posted April 29, 2005 Woss goin' on then Andy. You got 2 reverses ?. Non synchro ? You want to double declutch when braking hard for a corner IN REVERSE . Go on then tell us what you drive 🤔 Link to comment Share on other sites More sharing options...
Myles Posted April 29, 2005 Author Share Posted April 29, 2005 a BEC, obviously. Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
susser Posted April 29, 2005 Share Posted April 29, 2005 oright then Myles woss a BEC then Link to comment Share on other sites More sharing options...
Myles Posted April 29, 2005 Author Share Posted April 29, 2005 Bike Engined Car. In general, they need a special solution for reversing. Some of them use an electric reverse, others a mechanical reverse-box powered via the normal transmission. These are almost always seperate boxes - so you'll effectively get as many reverse gears as forwards... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
mav Posted April 29, 2005 Share Posted April 29, 2005 Bike Engined Car Link to comment Share on other sites More sharing options...
susser Posted April 29, 2005 Share Posted April 29, 2005 DOH ! 😳 Link to comment Share on other sites More sharing options...
Nifty Posted April 30, 2005 Share Posted April 30, 2005 2 reverse gears...pah ❗ I frequently have the choice of 24 or 36 *tongue* As Peter said earlier double declutching does nothing when trying to connect a moving shaft to a stationary shaft.Similarly, if you lose your clutch you can change between forward gears or drop into neutral but you won't get the car off the line or backwards without stopping it and then starting in gear (this isn't strictly true but the alternative involves brute force and likely gear damage ... as well as a well timed application of throttle to lurch you forward/back rather than stopping). I learnt this the interesting way when the line between master and slave failed on my Mini when I was a considerable distance out in rural Victoria. Keep off the straight and narrow 😬 Link to comment Share on other sites More sharing options...
Myles Posted May 27, 2005 Author Share Posted May 27, 2005 Pah! I'm still confused. I've been mixing single and double-declutches into reverse by way of investigation. The Focus will pop into reverse easily and without graunching immediately with a single-declutch - but even if I wait 5 or so seconds between a double-declutch, I get an engagement graunch (felt rather than heard - I'm not grinding teeth)... WossitallaboutAlfie? Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Colin Mill Posted May 27, 2005 Share Posted May 27, 2005 Caterham have thought of eveything: by arranging that nice input shaft rumble you can time the engagement of reverse perfectly. Just get the stick over to the left, drop the clutch and as the rumble is about to stop snick it in. And there we all were thinking it was a fault. 😬 BTW I think double declutching into reverse while rolling forward requires running the engine backwards! Colin Link to comment Share on other sites More sharing options...
Myles Posted May 27, 2005 Author Share Posted May 27, 2005 BTW I think double declutching into reverse while rolling forward requires running the engine backwards ...I'm not that mechanically unsympathetic. Car ain't moving. Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Colin Mill Posted May 27, 2005 Share Posted May 27, 2005 No, I'm not either (Ok I did it once in my tin-top to see if it was a syncro reverse - it was) Does the input shaft rumble die away when you press the clutch down in neutral? I wonder if you have just enough clutch drag to keep the input shaft turning. I found that If I wait for the input to definitely stop then I only have about a 30% chance of getting the thing into reverse - perhaps its because its new. The carefully timed snick seems the only reliable way. Link to comment Share on other sites More sharing options...
Myles Posted May 27, 2005 Author Share Posted May 27, 2005 I *am* talking about the Focus - the 7 is a whole-different ball-game and I rarely double-declutch at all in that. This is a pretty-academic discussion - as someone pointed out - there's little point in DD'ing into reverse - but I'm still trying to work out why the change is smoother with virtually no delay and with no assistance from a DD... Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
susser Posted May 27, 2005 Share Posted May 27, 2005 Sometimes you can't get into reverse because the dogs don't line up or the synchro cone teeth are point to point. The answer then is to engage whilst the shaft is still turning. The specified clutch spin down time for my BMW is 9 seconds. So you have got to engage reverse before the elapse of 9 seconds if you want the dogs to be still moving (slowly) when you snick em in. Kind of thing. Type stuff. Link to comment Share on other sites More sharing options...
Colin Mill Posted May 27, 2005 Share Posted May 27, 2005 'sright - good explaination on http://www.singster.co.uk/mascot%20mar-apr%202003%20(4).html but I don't see why they say DD can cause undue wear on the synchro rings, not unless you keep cocking it up. I never got out of the habit from driving old Landrovers and Fiat 500s where the synchros were absent either by design or age. Link to comment Share on other sites More sharing options...
Myles Posted May 27, 2005 Author Share Posted May 27, 2005 Haven't read that article yet - but assuming you're not blipping the throttle(heel'n'toe) during a DD (almost impossible for me to manage in the Focus), then it's very likely that the engine-speed has dropped way-too-low and therefore the synchros will take a large battering as the engine is driven back up to speed. I can only really to a decent DD (including blip) in the Focus in situations where you're just blending your speed down (across a gear-boundary) without braking. Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
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