aleda Posted June 25, 2015 Report Share Posted June 25, 2015 Hi all, having joined the 'cracked diff club' I have been researching on here and came across a post that stated one reason for cracked diff mounts was poor use of overdrive. Would appreciate advice on using overdrive correctly, it was completely overhauled in 2011. Quote Link to post Share on other sites
mike3md Posted June 25, 2015 Report Share Posted June 25, 2015 Not sure how much searching on "overdrive" you have done, but did you see this? http://www.tr-register.co.uk/forums/index.php?/topic/51488-am-i-using-the-overdrive-properly-or-abusing-it/?hl=overdrive Mike Quote Link to post Share on other sites
TR5tar Posted June 25, 2015 Report Share Posted June 25, 2015 (edited) Hi Christine (Is that you or the car?),I remember a thread some months ago where the use and (perceived) abuse of overdrive was discussed - http://www.tr-register.co.uk/forums/index.php?/topic/51488-am-i-using-the-overdrive-properly-or-abusing-it/?hl=overdrive Overdrive being relatively new to me at that time, it was a useful guide. However, there are differing opinions (as is often the case). Some feel that no or little special treatment is required, whereas others feel differently. What I do nowadays is always disengage before changing gear, and I always try to hold the revs constant while I disengage (rather than coming off the power). It makes for a smooth change in my car, but for others it'll be different I'm sure. Darren P.S. Mike beat me to it with the link (above)! Edited June 25, 2015 by TR5tar Quote Link to post Share on other sites
john.r.davies Posted June 25, 2015 Report Share Posted June 25, 2015 (edited) No need to disengage gear/clutch. When engaging overdrive at a constant speed, lift the throttle slightly. And on disengaging, press down, again slightly. This will minimise the jolt going in either direction, due to a mismatch between the wheels' and engine speed as the o/d engages/diengages, and any strain on the drive train. That's all! John Edited June 25, 2015 by john.r.davies Quote Link to post Share on other sites
stuart Posted June 25, 2015 Report Share Posted June 25, 2015 Just keep your foot down going in or out of overdrive. Stuart. Quote Link to post Share on other sites
littlejim Posted June 25, 2015 Report Share Posted June 25, 2015 Just keep your foot down going in or out of overdrive. Stuart. That technique gives me a 'clunk' free result. Quote Link to post Share on other sites
TR NIALL Posted June 25, 2015 Report Share Posted June 25, 2015 You really need Power On when Engaging OD makes for a much smoother engagement. Quote Link to post Share on other sites
mike3md Posted June 25, 2015 Report Share Posted June 25, 2015 Followed the previous thread on using overdrive, and see similar advice here (from some) about keeping some throttle on when coming out of overdrive, and understand the reasons. I always find that counterintuitive if changing down and using engine braking - where the natural inclination is to lift off the throttle, and probably apply the right foot to the middle pedal, as you come down through the gears (eg o/d 4th to 4th, to 3rd etc). I appreciate that this can be overcome by heel and toeing, if you have the ankle dexterity to do it. If there is time on slowing I therefore tend to de clutch while flicking the o/d out. Mike Quote Link to post Share on other sites
RogerH Posted June 25, 2015 Report Share Posted June 25, 2015 Hi Mike, indeed changing down has that reverse logic of increasing engine speed. However this is to allow the road speed and engine speed to match - otherwise you don;t have engine braking but gearbox breaking/braking instead. Pressing the clutch is for cowards Roger Quote Link to post Share on other sites
mike3md Posted June 25, 2015 Report Share Posted June 25, 2015 Roger, Always more retardation effect if the engine speed and road speed don't match! ;-) .....but pressing the accelerator while slowing down (and for most, not at the same time using the foot brake) feels odd, especially as drive is still engaged. Not the same as heel and toe, where the clutch is also used (most of the time). Mike Quote Link to post Share on other sites
stuart Posted June 25, 2015 Report Share Posted June 25, 2015 You should be reading the road better so you are in the correct gear for that particular situation. Stuart. Quote Link to post Share on other sites
peejay4A Posted June 26, 2015 Report Share Posted June 26, 2015 I engage it when I need it and disengage when I don't. I just concentrate on the road. No special technique required. Quote Link to post Share on other sites
ianc Posted June 26, 2015 Report Share Posted June 26, 2015 If overdrive is engaged with little throttle, there will be a jarring of the transmission - undesirable. If overdrive is disengaged on the over-run, the rear wheels may be locked momentarily - highly undesirable! To get smooth engagement of overdrive, have the throttle hard open - if the overdrive doesn't like this, it needs to be checked by a specialist. To get smooth disengagement, just press the throttle very lightly as the switch is flicked. Ian Cornish Quote Link to post Share on other sites
Superaquarama Posted June 27, 2015 Report Share Posted June 27, 2015 (edited) To get smooth engagement of overdrive, have the throttle hard open - if the overdrive doesn't like this, it needs to be checked by a specialist. Although I think you need to be somewhat more gentle when not in 4th gear, which I've always understood is why some mfrs such as Jaguar only allowed o/d via top gear. Edited June 27, 2015 by Superaquarama Quote Link to post Share on other sites
ianc Posted June 27, 2015 Report Share Posted June 27, 2015 Early TR2s had the 22/1275 Laycock overdrive, which used 1.125" operating pistons and was on top gear only. A change was made to the 22/1374 unit, which uses 1.375" pistons and operates on 2nd, 3rd and top gears. The 22 refers to the fact that the overdrive fitted on TRs had a gear ratio of 0.82, and if you divide 1 by 0.82 you will get 1.2195, so an increase in output speed of 21.95%, which Laycock rounded to 22. There were other versions giving as much as 32% increase in output speed - available on Standard 10, for example! Ian Cornish Quote Link to post Share on other sites
stuart Posted June 27, 2015 Report Share Posted June 27, 2015 To get smooth engagement of overdrive, have the throttle hard open - if the overdrive doesn't like this, it needs to be checked by a specialist. Although I think you need to be somewhat more gentle when not in 4th gear, which I've always understood is why some mfrs such as Jaguar only allowed o/d via top gear. The only one you really need to be a little careful of is with the IRS cars using 2nd overdrive, there can be a bit of a violent engagement if used at full chat! Jaguars use of overdrive only on top was because the amount of torque available and their use of the "Compact" overdrive unit, that said my 3.8 MK2 overdrive survived many years of heavy use of O/drive in 2/3/4 but that was with heavy re-enforcing of rear axle Panhard rod mount and torque arm mounts. Stuart. Quote Link to post Share on other sites
Superaquarama Posted June 27, 2015 Report Share Posted June 27, 2015 (edited) my 3.8 MK2 overdrive survived many years of heavy use of O/drive in 2/3/4 but that was with heavy re-enforcing of rear axle Panhard rod mount and torque arm mounts. Stuart. Interesting, Stuart ! Can you recall you managed to wangle o/d in the lower gears, or did you just bypass the switch ? I inadvertently did so with a Volvo P1800 once after a clutch change and it worked in all gears. Once put it into o/d reverse in the middle of Madrid, made a noise like wheels spinning and expected to have jiggered it, but fortunately no harm done ! Edited June 27, 2015 by Superaquarama Quote Link to post Share on other sites
stuart Posted June 28, 2015 Report Share Posted June 28, 2015 Your right it was with the switch bypassed but on the Jag there is a large warning segment on the column that lights up and says "Overdrive" and we did all know about never reversing with it in back then as we raced them as well. Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted June 28, 2015 Report Share Posted June 28, 2015 After switching on the overdrive there is maybe a second's delay before it engages. At the exact moment it is due to engage I lift the throttle and re-apply it Switching out of o/d I momentarily dip the clutch and blip the throttle, like a double de-clutch. Have done that for decades. And never needed an od rebuild. Peter Quote Link to post Share on other sites
stillp Posted June 28, 2015 Report Share Posted June 28, 2015 After switching on the overdrive there is maybe a second's delay before it engages. Seems a bit sluggish Peter? Perhaps you do need an OD rebuild! Pete Quote Link to post Share on other sites
Peter Cobbold Posted June 28, 2015 Report Share Posted June 28, 2015 (edited) Pete, It has worked like that for many years. My view is that rebuilds of anything classic-related carry their own risk these days, mainly to due with QC on repro parts. Some repro gearbox parts are I gather suspect. So if it anything on the 6 works "OK" I leave well alone. Peter And for good measure I've kept a spare od gearbox, gearbox was rebuilt around 1985. Edited June 28, 2015 by Peter Cobbold Quote Link to post Share on other sites
stillp Posted June 28, 2015 Report Share Posted June 28, 2015 Peter, I agree - if it ain't broke, etc. My O/D is virtually instant though, unless it's very hot. Pete Quote Link to post Share on other sites
David James Posted June 28, 2015 Report Share Posted June 28, 2015 I mainly use the overdrive on 4th as a 5th gear with clutch up and down. Could see little point on using the overdrive on 2nd and 3rd with the type of driving I did in my 2. Why would one need 7 gears for road use with a flexible engine? Like a manual XJ6 S1 with overdrive I had for a while both overdrives engaged quickly and seemed to appreciate the cossetting use of the clutch. Perhaps I was too old to learn to adapt to any new driving styles! Regards David Quote Link to post Share on other sites
stuart Posted June 29, 2015 Report Share Posted June 29, 2015 Depends on which overdrive you have, early A type was instantaneous as it had continuous built pressure and engaged with quite a discernible thump, later A type still had continuous pressure but had a cushioned engagement which though still instantaneous didnt have the associated thump. J type overdrives as they have to build pressure everytime do take a second or so to engage and put less of a strain on the drive train. Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted June 29, 2015 Report Share Posted June 29, 2015 Depends on which overdrive you have, early A type was instantaneous as it had continuous built pressure and engaged with quite a discernible thump, later A type still had continuous pressure but had a cushioned engagement which though still instantaneous didnt have the associated thump. J type overdrives as they have to build pressure everytime do take a second or so to engage and put less of a strain on the drive train. Stuart. Thanks Stuart, Mine's a J type. So what I had been thinking was a fault isnt a fault after all. Its cured !! - after nearly 40 years. Peter Quote Link to post Share on other sites
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