Tipidave Posted October 3, 2022 Report Share Posted October 3, 2022 I have read various threads in the topic of converting a std 1200 herald to an overdrive and I find myself somewhat bemused by all of the options and potential pitfalls. Can anyone describe what would be the best overdrive to look for and talk me through the steps needed to convert? Link to comment Share on other sites More sharing options...
Colin Lindsay Posted October 3, 2022 Report Share Posted October 3, 2022 I wrote an article on a simple conversion for the current Courier, if you've got it. J-type overdrive Spitfire 3-rail gearbox and mount, Vitesse propshaft, a switch, and some cable. Needs no cutting or balancing as it's all a straight fit into the existing setup. It gives a 25% reduction in revs, and is about the simplest conversion you'll do. Pitfalls are buying the gearbox, which is always a gamble - worn internals or else a duff Overdrive, but you just have to take the chance, and on mine the solenoid was sticking so needed cleaning out. Otherwise it fitted easily and has worked very well ever since. Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 3, 2022 Report Share Posted October 3, 2022 a Dtype is more straight forward and well within the power of a 1200 J type is a more improved evoluton but D types were the std fit on all exept the younger 1500 spit with a single rail box what ever you get you will need the appropriate adaptor and a new mainshaft so needs a gearbox strip and use your current internals if they are ok Pete Link to comment Share on other sites More sharing options...
daverclasper Posted October 3, 2022 Report Share Posted October 3, 2022 Mike Papworth sells complete units (maybe depends what he has as stock, as getting rarer, I imagine?), which I assume he will have checked/reconditioned and offered a guarantee/. Maybe a safer, more straightforward way of going about it Link to comment Share on other sites More sharing options...
Clive Posted October 3, 2022 Report Share Posted October 3, 2022 The biggest downside is the cost🤐 For a complete conversion that is guaranteed good (as opposed to "I was told it was good when I bought it") expect to pay £1000, probably double that for a reconditioned setup. Yes, cheap od boxes do turn up, but not often, and usually unknown condition. You pays your money etc. a 1200 herald should be OK with an OD on the level/mild inclines, but may struggle going up anything more in OD top. However, my experience says OD is a fantastic bit of kit if you drive any distance. No use around town, but good A road through to motorways it is a godsend, everything is much more relaxed. However, with the costs involved, do decide if it would present value to you. Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 3, 2022 Report Share Posted October 3, 2022 the cost effective option is to swap to a 3.63:1 diff we have a locql 1200 and it runs very well on this higher ratio diff certainly a much simpler job Pete Link to comment Share on other sites More sharing options...
Colin Lindsay Posted October 3, 2022 Report Share Posted October 3, 2022 No-one these days is making gearboxes nor sufficient parts, so buying any is a gamble. All you can do is buy from a reputable breaker who will replace if anything fails. That's my second Chic Doig box, and both were £175. Why pay hundreds more for effectively the same thing? Add a second-hand Vitesse prop £30 - £50, switch, mount and wiring maybe £30 max, and it's still cheap. I don't use O/D top for hills anyway, any more than I'd use 5th or 6th in the modern, so off for hills and town centres (unless O/d 3rd) and back on for long cruises on the carriageway. I can only quote from experience and so far, so good. Link to comment Share on other sites More sharing options...
Tipidave Posted October 4, 2022 Author Report Share Posted October 4, 2022 Thanks for all of the answers. I think that I will try to piece together all of the components… I am not in a rush. 👍 Link to comment Share on other sites More sharing options...
Tipidave Posted October 8, 2022 Author Report Share Posted October 8, 2022 As a bit of an aside… I have now received my October copy of the Courier and have read Colin’s most excellent article on installing an overdrive … I do like these little synchronicities in life. Just as I start to ponder a way forward… within a week a most useful article plops through my letterbox. So… thanks for that 👍👍👍😀😀 Link to comment Share on other sites More sharing options...
Tipidave Posted October 12, 2022 Author Report Share Posted October 12, 2022 Is there any reason that I should not use a spitfire 1500 gearbox with j type overdrive. I think it has the switch gear in the gear knob. Thanks David Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 12, 2022 Report Share Posted October 12, 2022 most 1500 used the single rail gearbox this would need a change of clutch disc to a rolled spline shaft from your 10 spline machined shaft this may involve a complete change of cover and a redrill of the flywheel others have suggested whats needed in this swap over Pete Link to comment Share on other sites More sharing options...
Clive Posted October 12, 2022 Report Share Posted October 12, 2022 14 minutes ago, Tipidave said: Is there any reason that I should not use a spitfire 1500 gearbox with j type overdrive. I think it has the switch gear in the gear knob. Thanks David No reason at all, but be aware that: 1. Clutch plate needs changing to a dolomite 1300 type. This assume you have a diaphragm clutch, not the early coil spring type. 2. OD switcjes on gearknobs can be an issue, the column type is more reliable and easier/cheaper to source. 3. The 1500OD box is longer that the 3 rail types. You will need a custom length propshaft. With big flange at the front, small at the back to fit your existing diff. There is a "modifcation" (bodge) I had to do. Space the engine forward an inch, then you can use a vitesse non-od prop, flange size issue still there. (I did the swap at the weekend, needed the car for work on the Monday. But it worked fine, I did many thousands of miles, as did subsequent owners) Link to comment Share on other sites More sharing options...
Colin Lindsay Posted October 12, 2022 Report Share Posted October 12, 2022 On 08/10/2022 at 08:06, Tipidave said: As a bit of an aside… I have now received my October copy of the Courier and have read Colin’s most excellent article on installing an overdrive … I do like these little synchronicities in life. Just as I start to ponder a way forward… within a week a most useful article plops through my letterbox. So… thanks for that 👍👍👍😀😀 Autographs / additional information available on request... However as Clive says above, using the 1500 single rail box means that it sits further back in the car, so you'll need to cut and balance a prop and probably have to trim the centre tunnel to bolt it on. 3-rail is an inch at least shorter and a straight fit, hence I went for the simplest option. Link to comment Share on other sites More sharing options...
johny Posted October 12, 2022 Report Share Posted October 12, 2022 2 hours ago, Tipidave said: Is there any reason that I should not use a spitfire 1500 gearbox with j type overdrive. I think it has the switch gear in the gear knob. Thanks David Also first gear ratio will be different going from 3.75 to 3.5 to 1 but not sure how much difference that will make to pull aways in your car.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted October 12, 2022 Report Share Posted October 12, 2022 On Heralds, first gear was recommended for steep hill starts only. Moving off in second was recommended in the handbook! Link to comment Share on other sites More sharing options...
johny Posted October 12, 2022 Report Share Posted October 12, 2022 Even for the 1200 as I believe the 1360 kept the same 3.75 ratio but of course had more power? Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 12, 2022 Report Share Posted October 12, 2022 most cars with a crash 1st were more hill start /emergency low ratio, start in 2nd was common practice back in the old days it disappeared when speeds increased and diff ratios all went higher ratio to aid the revs /speed and having 4 or 5 gears on synchro became needed to spread the torque range across the speed range Pete Link to comment Share on other sites More sharing options...
johny Posted October 12, 2022 Report Share Posted October 12, 2022 Suppose we need someone who has done the conversion to comment on how starts/hillstarts in a 1200 Herald compare before and after. I know my Vitesse would actually be better with a higher first gear ratio... Link to comment Share on other sites More sharing options...
Pete Lewis Posted October 12, 2022 Report Share Posted October 12, 2022 we have a local 1200 + 3.63:1 diff he has some good hills around 1 in 8 but need to ask him to do a hill start with 4 up and see if the clutch sliptime gets him going Pete Link to comment Share on other sites More sharing options...
johny Posted October 12, 2022 Report Share Posted October 12, 2022 Ha, yes if it can do that then a 1500 gearbox is no problem👍 Link to comment Share on other sites More sharing options...
Wagger Posted October 12, 2022 Report Share Posted October 12, 2022 On 08/10/2022 at 08:06, Tipidave said: As a bit of an aside… I have now received my October copy of the Courier and have read Colin’s most excellent article on installing an overdrive … I do like these little synchronicities in life. Just as I start to ponder a way forward… within a week a most useful article plops through my letterbox. So… thanks for that 👍👍👍😀😀 Yes, Colin did a grand job both with the task and the documentation. He deserves a reward from the cars. Hope it does monster mpg Colin. Link to comment Share on other sites More sharing options...
Tipidave Posted October 14, 2022 Author Report Share Posted October 14, 2022 I may have sourced a suitable candidate box to start the conversion process… can anyone help to diagnose the following numbers that are stamped on the candidate… -FC 67790 this is stamped, the following are in the casting--303546---N295---303709R, thanks in anticipation david Link to comment Share on other sites More sharing options...
Colin Lindsay Posted October 14, 2022 Report Share Posted October 14, 2022 FC6**** will be Spitfire Mk2, probably a D-type overdrive if it has one. Needs a relay, but the plus side is that the solenoids are a fifth of the price of J-type... Link to comment Share on other sites More sharing options...
johny Posted October 14, 2022 Report Share Posted October 14, 2022 That should be pretty much identical to your existing box so no synchro on first gear but identical ratios and if needed most parts are transferable between the two👍 Link to comment Share on other sites More sharing options...
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