Jonathan Pryse Posted February 22, 2019 Report Share Posted February 22, 2019 Second newbie question.... Picking Spitfire 1500 up Saturday then driving home around M25.... Being born in 1967 I've never used overdrive before! I understand it's just an extra 'ratio' but when and how is it used? Is 4th + overdrive work a bit like 5th? I've heard people say you can use it from 3rd too?? Not sure why you would want to. And most basic question is how do you engage? I assume clutch is needed at same time as flicking the switch?? Just to reassure you it does work - I had it inspected before purchase!! Thanks for your kind responses in advance - it will make my journey far less daunting!! Link to comment Share on other sites More sharing options...
Paul H Posted February 22, 2019 Report Share Posted February 22, 2019 You don’t need to use your clutch , I take my foot off the accelerator and flick the switch then use the accelerator gently . I’m sure you will receive more advice from more experienced users. I don’t bother using overdrive in 3rd gear . Don’t forget to switch off overdrive when slowing down. I found adding a warning light for overdrive very very useful . I have a Vitesse Mk 2 Paul 1 Link to comment Share on other sites More sharing options...
Clive Posted February 22, 2019 Report Share Posted February 22, 2019 Yes, think of it as a 5th gear. 3rdOD can be useful in traffic sometimes, but I rarely use it. You will love it as you whizz round the M25 (hopefully!), and instantly appreciate the advantages on a longer trip. Welcome to ownership. Hopefully you will enjoy it and use it a great deal. I see you are near Dover/Folkstone, so idea place for exploring Europe.... 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 22, 2019 Report Share Posted February 22, 2019 The od will work in 3rd and 4th, but 3rd od is same ratio as 4th , as the ratios are not spread out well by triumph You can use throttle or just feather the clutch to smooth out any head jerking changes, You can overtake in 3rd and flick to re use the toque band of the engine, without any foot work it will be fine changing under power Its all down to how you want to your driving style, use either foot to smooth out a change or not its all,down to how you drive. Obvious smoothed is less stress on the whole drive live but there are times when enthusiasm wins Pete 1 Link to comment Share on other sites More sharing options...
RogerH Posted February 22, 2019 Report Share Posted February 22, 2019 Hi Jon, I have a 4A with better spaced gear ratio's (and 22% OD ratio) so 3rd and 3rd/OD compliment each other. Your 3rd and 3rd/OD (albeit another 4th) will be handy on very hilly runs (think Black Forrest etc) . 3rd gear around the hairpins then click into 3rd/OD for the short straight, then back into 3rd for next hairpin. Saves a lot of leg work. Be kind to the OD when, in particular, coming out of OD. This can be mighty rough. My method - in 4th get up to 45-50mph - leave throttle as is and engage OD. The revs will drop. All should be smooth. From 4th/OD to 4th - keep a steady throttle (do not let the revs drop) disengage OD - the revs will rise - ease off the throttle to slow down - keep it smooth. You can use the clutch at any time but why would you. This simply causes more wear due to use. OD is a blessing on long runs in particular. Enjoy the car. Roger . 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 22, 2019 Report Share Posted February 22, 2019 when it comes to smooth changes the A type is more harsh than a D type and J type is less harsh than a D type things got damped as the units evolved .all do a good and reliable job Pete Link to comment Share on other sites More sharing options...
RogerH Posted February 22, 2019 Report Share Posted February 22, 2019 1 hour ago, Pete Lewis said: when it comes to smooth changes the A type is more harsh than a D type and J type is less harsh than a D type things got damped as the units evolved .all do a good and reliable job Pete Hi Pete, thanks for that. D & J type = unknown territory Roger Link to comment Share on other sites More sharing options...
JumpingFrog Posted February 22, 2019 Report Share Posted February 22, 2019 4 hours ago, Pete Lewis said: The od will work in 3rd and 4th, but 3rd od is same ratio as 4th , as the ratios are not spread out well by triumph This is true for "close ratio" gearboxes (GT6, Vitesse, TR7, Dolly 1850) which have 3rd = 1.25. But not so with the wider ratios in a Spitfire, 3rd = 1.39:1. Assuming a 25% J-Type, 3rd + OD is 1.1:1, which is a decent intermediate gear for low-speed cruising. E.g. with a 3.63 diff, 30mph @ ~1800 rpm or 40mph @ ~2400rpm. Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 22, 2019 Report Share Posted February 22, 2019 Atype has an accumaltor to store up energy ( from memory) and is a more mechanical hydraulic solenoid shift D type is just mechanical hydraulic shift J type is just hydraulic probably all eveloved to make cost more effective than was it any good or not, but as they all work for years its all water under the bridge Pete Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 22, 2019 Report Share Posted February 22, 2019 Ive just rebuilt a spitty with vitesse 2nd 3rd ratios , makes a good job less thrash more varrooom Pete Link to comment Share on other sites More sharing options...
JohnD Posted February 22, 2019 Report Share Posted February 22, 2019 JF, If OD 3rd isnt the same as normal 4th, its damn near! And that can useful if you want be able to slip between 3rd & 4th easily, just leave in 3rd and use the O/d, eg high speed curvy, if not bendy roads. If you like 'smooth driving' and why not, there can be slight jolts on moving in and out of O/d, as the engine accomodates the change in speed that the road wheels dictate. So, when changing into O/d, feather the throttle to allow a reduction in engine speed more easily, and apply slightly more throttle when coming out, to aid the speed up. When your passneger can say, what's that lever you keep using on the column? You know you're a master! The probelm may arise when slowing right dwon, and into second, as the cut out on the gearbox will disngage O/d, but as soon as you move back up to 3rd, your in 4th (O/d 3rd, 4th or near to it) . Can be embarassing! There are circuits published that will electronicvally disengage your O/d selector switch/lever so that you always go back up to normal/3rd. My solution has benea small warning light that works in parallel with the O/d switch. JOhn 1 Link to comment Share on other sites More sharing options...
Mjit Posted February 22, 2019 Report Share Posted February 22, 2019 I've always flat shifted in both my o/d equiped 2.5 saloon and Spitfire and never had any issues. My Spitfire's got a bits'a drive train, with 1300 engine/1500 gearbox/god knows diff. and find o/d 3rd very useful as it's not quite the same as 4th. Around town the car's much happier with the extra RPM of o/d3rd vs 4th - though as a 1300cc it also has less torque than a 1500cc, and when waiting for an A road overtaking gap being able to drop o/d3rd to 3rd with just the flick of a switch helps you make progress. I don't think anybody's covered how an O/D works. On a 1500 Spitfire it should be a J-type, which means a little in/out button on the top gearstick (and if you keep getting electric shocks, with the insulation rubbed through on the wires that run down inside the gear stick). Stuck on the back of the engine you have the same 4 speed gearbox as every other 1500 Spitfire but stuck on the back of that, rather than just a lump of metal that covers the output shaft up to the point it bolts to the prop. shaft you have the O/D unit. This is basically a separate, 2 gear gearbox but rather than being operated by a second gear stick (like the similar high/low ratio selector (2 speed gearbox) on an old Land Rover) it contains a little hydraulic pump and a valve controlled by an electrical circuit...which brings us back to the switch at the top of the gear stick. Flick the switch "in" and you complete the circuit to the valve. The valve opens and feeds pressurised oil in to the 'in' side of the O/D. The oil foces the gears in to the 'in' position and the output shaft of the O/D now turns faster than the output shaft of the main gearbox. Flick the switch 'out', the circuit closes, the valve closes, the oil stops being pumped to the 'in' side of the O/D, and the gears fall back to the 'out' position, at which point the output shaft of the O/D turns at the same speed as the output shaft of the main gearbox. Slightly over-simplified but hopefully gives you an idea of what's going. 1 Link to comment Share on other sites More sharing options...
Colin Lindsay Posted February 22, 2019 Report Share Posted February 22, 2019 It does, so many thanks. I use O/D third for town centre driving; just flick it in or out from the column switch and it's very simple without taking your hands off the wheel, but I find that O/D 4th makes quite a difference for higher speed cruising eg dual carriageways or motorways. Mine is a J-type from a Dolomite 18/50 so no idea of the ratio, but it feels so much more relaxed. Link to comment Share on other sites More sharing options...
Anglefire Posted February 22, 2019 Report Share Posted February 22, 2019 I slightly regret not getting a spitfire with O/D - but guess one can be retrofitted without too much drama - though I assume the prop is a different length? Link to comment Share on other sites More sharing options...
Clive Posted February 22, 2019 Report Share Posted February 22, 2019 yes, prop is a shorter one. Mounts etc are different, but wiring is a doddle on a 1500. Local chappie will be refurbing a 1500 OD box in the next few weeks..... (apparently from a very low mileage dolomite 1500 that dissolved on a driveway). Link to comment Share on other sites More sharing options...
Anglefire Posted February 22, 2019 Report Share Posted February 22, 2019 Hum, wonder what the cost of that will be...... Link to comment Share on other sites More sharing options...
Clive Posted February 22, 2019 Report Share Posted February 22, 2019 I can ask..... and check what it comes with. 1 Link to comment Share on other sites More sharing options...
JumpingFrog Posted February 22, 2019 Report Share Posted February 22, 2019 5 hours ago, JohnD said: JF, If OD 3rd isnt the same as normal 4th, its damn near! I wouldn't go as far as damn near, I agree it's close. Here's a table anyway. Lower bit of the table are speeds in MPH for different revs. Link to comment Share on other sites More sharing options...
JohnD Posted February 22, 2019 Report Share Posted February 22, 2019 Anglefire, You can't just bolt an O/d on the back of an ordinary gearbox. Needs different output shaft. J. 1 Link to comment Share on other sites More sharing options...
Anglefire Posted February 22, 2019 Report Share Posted February 22, 2019 Thanks John, Clive did clarify that point. Link to comment Share on other sites More sharing options...
Jonathan Pryse Posted February 23, 2019 Author Report Share Posted February 23, 2019 20 hours ago, Mjit said: I've always flat shifted in both my o/d equiped 2.5 saloon and Spitfire and never had any issues. My Spitfire's got a bits'a drive train, with 1300 engine/1500 gearbox/god knows diff. and find o/d 3rd very useful as it's not quite the same as 4th. Around town the car's much happier with the extra RPM of o/d3rd vs 4th - though as a 1300cc it also has less torque than a 1500cc, and when waiting for an A road overtaking gap being able to drop o/d3rd to 3rd with just the flick of a switch helps you make progress. I don't think anybody's covered how an O/D works. On a 1500 Spitfire it should be a J-type, which means a little in/out button on the top gearstick (and if you keep getting electric shocks, with the insulation rubbed through on the wires that run down inside the gear stick). Stuck on the back of the engine you have the same 4 speed gearbox as every other 1500 Spitfire but stuck on the back of that, rather than just a lump of metal that covers the output shaft up to the point it bolts to the prop. shaft you have the O/D unit. This is basically a separate, 2 gear gearbox but rather than being operated by a second gear stick (like the similar high/low ratio selector (2 speed gearbox) on an old Land Rover) it contains a little hydraulic pump and a valve controlled by an electrical circuit...which brings us back to the switch at the top of the gear stick. Flick the switch "in" and you complete the circuit to the valve. The valve opens and feeds pressurised oil in to the 'in' side of the O/D. The oil foces the gears in to the 'in' position and the output shaft of the O/D now turns faster than the output shaft of the main gearbox. Flick the switch 'out', the circuit closes, the valve closes, the oil stops being pumped to the 'in' side of the O/D, and the gears fall back to the 'out' position, at which point the output shaft of the O/D turns at the same speed as the output shaft of the main gearbox. Slightly over-simplified but hopefully gives you an idea of what's going. Really useful explanation as to how it works. Helps a lot when you understand what is happening when the overdrive is engaged. Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 23, 2019 Report Share Posted February 23, 2019 its an epicyclic gearbox the cone clutch is on its outer 'ring' the hydraulic pistons engage or disengage the clutch which is a tapered facing into a cone . the rate of hydraulic operation determines the rate of engagement and from A D and J this has improved to smooth out changes as the unit designs evolved over the years each type has different power capabilities . Pete Link to comment Share on other sites More sharing options...
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