thescrapman Posted November 9, 2020 Report Share Posted November 9, 2020 Bit of assistance needed. Converting a single rail 1850 box into a 3-rail box. My previous notes said it should be easy, but have hit 2 problems. What adaptor between gearbox and overdrive do you need to use, original is too tall, and leaves a gap, and more importantly, can you use the original single rail mainshaft, or is a different one needed? I am suspecting I may have messed up! Link to comment Share on other sites More sharing options...
johny Posted November 9, 2020 Report Share Posted November 9, 2020 I believe you have to get a special mainshaft ie a 3 rail one but with a big bearing tip to match the 1850 input shaft. They were being made at one stage but dont know if thats still the case.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted November 10, 2020 Report Share Posted November 10, 2020 Just a query when we're on the topic - is the 1850 input shaft still available, or does anyone have the spec / part number? I may need one and there have been a few unidentified NOS input shafts for same online, so I'd like to keep an eye out for one just in case. Link to comment Share on other sites More sharing options...
johny Posted November 10, 2020 Report Share Posted November 10, 2020 believe its TKC1268 and of course having the fine splines will need the Dolomite clutch friction plate. They must be quite rare as specific to the last of the line 1850s so NOS difficult but occasionally a used box comes up like the non OD one that hasnt sold for ages on ebay at 60quid.... Link to comment Share on other sites More sharing options...
68vitesse Posted November 10, 2020 Report Share Posted November 10, 2020 From Rimmers Dolomite parts manual. Regards Paul Link to comment Share on other sites More sharing options...
Colin Lindsay Posted November 10, 2020 Report Share Posted November 10, 2020 Same as GT6 MK3, then... but still hard to find. Thanks! Link to comment Share on other sites More sharing options...
68vitesse Posted November 10, 2020 Report Share Posted November 10, 2020 I have a three rail box with J type overdrive with fine input shaft in my Vitesse, when it shed two teeth from third gear on the cluster got replacement parts from Mike Papworth. Regards Paul Link to comment Share on other sites More sharing options...
Nick Jones Posted November 10, 2020 Report Share Posted November 10, 2020 Colin, it should be possible to transfer the internals from a single rail to 3 rail casing (any 4 synchro one) and pop any 4 synchro top housing/selector mech on it. You do use the single rail mainshaft. The single rail OD adapter (the long one) is quite tall where takes the selector rod in its original application and this part of it sits above the 3 rail casing split line. You might need to relieve the edge of the top housing to miss it but nothing more that I recall. It’s been 30 years since I did one mind, although I do have most of the parts to do another to hand. Nick Link to comment Share on other sites More sharing options...
Nick Jones Posted November 10, 2020 Report Share Posted November 10, 2020 20 hours ago, johny said: I believe you have to get a special mainshaft ie a 3 rail one but with a big bearing tip to match the 1850 input shaft. They were being made at one stage but dont know if thats still the case.... No. Only if you are trying to make a J type box that is the same length as the D type. For that you also need the ( now rare and expensive) OD adapter from an early 3 rail Dolly 1850 box. The mainshaft needed was never a factory but is available from Mike Papworth Nick Link to comment Share on other sites More sharing options...
thescrapman Posted November 10, 2020 Author Report Share Posted November 10, 2020 45 minutes ago, Nick Jones said: Colin, it should be possible to transfer the internals from a single rail to 3 rail casing (any 4 synchro one) and pop any 4 synchro top housing/selector mech on it. You do use the single rail mainshaft. The single rail OD adapter (the long one) is quite tall where takes the selector rod in its original application and this part of it sits above the 3 rail casing split line. You might need to relieve the edge of the top housing to miss it but nothing more that I recall. It’s been 30 years since I did one mind, although I do have most of the parts to do another to hand. Nick Length is not a problem, I need to get a propshaft anyway. Issue is the long adaptor having its internals open to the outside world at the top I am told. I don't have the bits to hand to look at, as someone else is putting them together for me. All I have is a 1500 Spitfire OD box and a 3 rail casing to look at and visualise. Trying not to buy a different ( and currently very very expensive) mainshaft and almost as expensive adaptor. Link to comment Share on other sites More sharing options...
johny Posted November 10, 2020 Report Share Posted November 10, 2020 As Nick says it looks from these pictures that the existing adaptor could be used as the only problem is the hole that would be left exposed in the face of the adaptor against the gearbox case and Im sure it wouldnt be impossible to plug this if necessary.... https://www.ebay.co.uk/itm/Triumph-Spitfire-MK4-1500-Overdrive-Adaptor-Plate/363161237257?hash=item548e18b709:g:7SEAAOSw8OteUtcX Link to comment Share on other sites More sharing options...
Peter Truman Posted November 10, 2020 Report Share Posted November 10, 2020 I've done it ie single into 3 rail 4 syncro case and selectors, yes the single rail adapter will fit the top hole doesn't get used the earlier Spit iV gasket is used theres enough sealing face. Beware the existing 3 rail reverse lever on the idler shaft it doesn't align with the 3 rail gear selectors and needs major surgery I think my problem was I used the single rail reverse idler shaft spacer which is longer maybe I should have used the shorter 3 rail spacer sleeve BUT would the single rail reverse idler gear then have cleared and engaged correctly? also there's a small washer that has to be fitted to the reverse selector rod to avoid engaging two gears simultanuosly! On our Spits conversion of J type and Single rail into a 3 Rai box casing I used the Spit IV J type 3 rail adapter which needed a 1in additional spacer annulus as the single rail mainshaft is 1in longer. Somewhere in my archives computer files I have my email comms with John Kipping then in NZ telling me what I needed and to watch out for he was very helpful and I'll always be in his debt! In the attached pic you'll notice the early Herald thinwall bellhousing it's been replaced with the later thicker alloy one same casting as cast iron one and far stronger. 3 Rail J Type Conversion - 1in Adapter.pdf Link to comment Share on other sites More sharing options...
thescrapman Posted November 10, 2020 Author Report Share Posted November 10, 2020 Extra info back from Gearbox man, the shaving of the adaptor is necessary as per Nick, and he had mis-read that there was an open hole. There is a breather that gets sealed by the gasket, and the other hole that isn't open to the outside. So my gearbox will,be done in a day or so, ready for collection. Glad my memory and notes were correct. Thunk there is a national shortage of mainshafts or some serious profiteering, Rimmers has single rail ones at over £300 now. And that is a standard one Link to comment Share on other sites More sharing options...
thescrapman Posted November 10, 2020 Author Report Share Posted November 10, 2020 peter, if you can find your comms with JK it would be very interesting Link to comment Share on other sites More sharing options...
Nick Jones Posted November 11, 2020 Report Share Posted November 11, 2020 15 hours ago, thescrapman said: Issue is the long adaptor having its internals open to the outside world at the top I am told. I don’t believe this is correct. There is a separate drilling at the top of the adapter that carries the selector rod in the single rail application, which is redundant when fitted to the 3 rail casing, but iirc has no internal link to anything else and can be ignored. I have the parts in question loose at home and can check this evening if you like? Edit: note to self..... read whole thread before replying. Glad its resolved Colin. Yes, parts are getting very pricey...... Think I paid £170 a couple of years back for a D type mainshaft with larger spigot...... Does perhaps mean that the box of oily scrap in the corner is actually of some value. Trying to get an MX5 box into my GT6 at present....... not a match made in heaven...... lots of mods (to the box, trying to minimise car mods) are needed, involving machine tools and TIG welders.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted November 11, 2020 Report Share Posted November 11, 2020 15 hours ago, thescrapman said: Issue is the long adaptor having its internals open to the outside world at the top I am told. I don't have the bits to hand to look at, as someone else is putting them together for me. All I have is a 1500 Spitfire OD box and a 3 rail casing to look at and visualise. I have photos of Herald 3-rail versus Spitfire single-rail for comparison; I know they're not Dolomite 1850 / GT6 boxes but they may help in giving some idea of the differences? Link to comment Share on other sites More sharing options...
thescrapman Posted November 11, 2020 Author Report Share Posted November 11, 2020 Colin Do you need fine spline ( later 1850) or course spline ( early 1850 and Mk3 GT6) input shaft? I may have a course one left over from the rebuilds of my 2 gearboxes. I needed to break a non OD box From a Mk3 GT6 to get a good layshaft cluster. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted November 11, 2020 Report Share Posted November 11, 2020 Lol now you're asking! I think mine just used the original clutch plate from a GT6 but I can't remember, it was purchased back in 2001 and hasn't really been out since 2005... I've found photographs taken at the time but can't remember if the close-up shots are the non O/D one that was removed and given away or the replacement, which was 3-rail 1850 Dolomite. The photos all appear to show coarse splines. If it's only the splines that differ then the next clutch can be changed to fit, but I'm almost certain it's coarse. In fact I can remember, when the gearbox was fitted in 2004 after the engine rebuild, reusing the old clutch plate and thinking I should really have bought a new one, in which case it's definitely the original GT6 version. The photos I have of an old input shaft being used as a clutch centralising tool show coarse splines. Link to comment Share on other sites More sharing options...
Peter Truman Posted November 11, 2020 Report Share Posted November 11, 2020 here's 2 pics of a 3 rail gearbox fitted with a J type O/D using the single rail Jtype OD gearbox to OD adapter, don't know who or when i was done but I found it when getting ready to convert a Dolly 1850 single rail into a 3 rail for my Mk2 Vitesse. The pic's show how the single rail adapter extends successfully above the 3 rail gearbox case. Link to comment Share on other sites More sharing options...
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