tegwin
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| posted on 18/3/09 at 10:46 AM |
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Overdrive driving
I have an overdrive fitted to the 4sp box on the TVR..
Its operated via an electrical switch on the gearknob..
I have wired it so it only works in 3-4 gear...
However.. how do I actually use it?
Presumably I work my way up through the gears until I am finished with 4th, and then what? Stand on the clutch, flick the switch and bring the
clutch up.... ? Im not sure how exactly one is supposed to drive with such a contraption attached!
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Xtreme Kermit
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| posted on 18/3/09 at 10:54 AM |
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I believe that you go 1, 2, 3, 3od, 4, 4od
As far as I can remember you do not need to dip the clutch but it has been a long time since I drove a car with overdrive.
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sickbag
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| posted on 18/3/09 at 10:56 AM |
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My father used to have a Jag with overdrive, although he only used it in fourth.
You just flick the switch to on or off - no need to use the clutch with it at all.
Finally back on the job!
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mcerd1
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| posted on 18/3/09 at 10:57 AM |
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I thought that it went something like:
1, 2, 3, 3OD, 4, 4OD (no clutch needed for the OD)
I've got it on the scimitar but I've not tried it yet - its been off the road since I was 2 years old  (its the next project once the
dax is finished)
[edit] damm, too slow again...
[Edited on 18/3/09 by mcerd1]
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chrsgrain
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| posted on 18/3/09 at 11:01 AM |
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I expect its the same as the o/d on the TR4 and 5, you don't need to use the clutch as its got a hydraulic clutch in the mechanism - so just use
it as an intermediate gear, 3, 3OD, 4, 4OD.... nice for gently dropping a cog to overtake.
Lots more information here
Chris
Spoing! - the sound of an irony meter breaking...
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sickbag
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| posted on 18/3/09 at 11:02 AM |
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I'm not sure if you'd get any benefit using it while in 3rd, as the ratio difference between 3rd with overdrive will be quite close to 4th
without overdrive. Although this was on a 4.2Ltr series 1.
[Edited on 18/3/09 by sickbag]
Finally back on the job!
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aka Keith
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| posted on 18/3/09 at 11:02 AM |
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My old spitfire had overdrive. And to concur with what has been said earlier it was , 1,2,3, 3OD, 4, 4OD, if you wanted to use it.
No need to use the clutch,
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mcerd1
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| posted on 18/3/09 at 11:06 AM |
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my dad had it on an old rangerover (perkins diesel conversion) - he only ever used OD in 4th on that one (no clutch)
I guess it depends on the ratios - any idea what they are ?
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t16turbotone
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| posted on 18/3/09 at 11:09 AM |
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if its a laylock overdrive, use in 3rd and fourth whenever you like, no clutch just switch in and out as you please, had o/d in my dolly sprint few
years back
make sure inhibit switch is good, if for any reason overdrive gets selected in reverse gear you will be left with many pieces on the drive
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tegwin
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| posted on 18/3/09 at 12:08 PM |
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Hmm.. Will see how it goes..... Not sure if it actually works yet... 
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Would the last person who leaves the country please switch off the lights and close the door!
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yellow melos
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| posted on 18/3/09 at 01:21 PM |
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Yeah, older relative used to have a triumph Dolamite with one on, you could not use it in 1st or 2nd due the the power of the eingine breaking them (
Yeah... even in a dolamite )
anyway, don't need to clutch.. the basically invoke a secondary planetary gear in the diff or gearbox that give a slighty higher ratio.
meant to be for those time that 4th is too high and 3rd is too low....gind of thing
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deezee
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| posted on 18/3/09 at 01:29 PM |
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My 1972 MGB GT had overdrive on 3rd and forth. I only used it in forth for motorway cruising really.
I loved driving around with the car in 3rd OD. You could flick it out of overdrive and instantly get 500rpm out the engine. Made overtaking loads
more fun. Its like an instant gearchange.
Ahhh, I want a sequential box now.
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Canada EH!
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| posted on 18/3/09 at 03:02 PM |
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Old Healey racers used overdrive 3rd for corners that were a little too fast for 3rd and pulled the engine too low in 4th, 4th OD for the back
straight at Mosport.
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BenB
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| posted on 18/3/09 at 05:18 PM |
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Do overdrive units take any power during normal running?!?! Just wondered about adding one to the BEC to lower cruising RPMs!!! Wonder how much grunt
an overdrive box will take....
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BenB
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| posted on 18/3/09 at 05:24 PM |
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Looks like a Hone overdrive will take the grunt. Shame they're rare as hen's teeth....
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Mix
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| posted on 18/3/09 at 05:30 PM |
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Hi
The OD on my Scimitar was always available, (in third and fourth), and as such I believe always taking energy to drive. It was actuated by oil
pressure using the gearbox oil as a transmission fluid, (I found this out when the OD became sluggish, restoring the gearbox oil level fixed the
problem).
In past days OD was nice to have but nowadays with more flexible engines it's just added weight.
Regards Mick
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rusty nuts
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| posted on 18/3/09 at 06:41 PM |
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Might pay to ease off the throttle as you engage the overdrive . My brother didn't and smashed his overdrive and twisted the splines on the
third motion shaft of the gearbox. Had to use a sledge hammer to smash the overdrive off of the gearbox.
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