rogerguzzi Posted January 31, 2019 Share Posted January 31, 2019 Hello All As you know I have my Spitfire single rail gearbox in pieces I have made a new clutch bearing carrier with a lip seal(instead of scroll type) plus the later ones are longer? Then my mind started to fantasize about having overdrive on 2nd gear! My reasoning is I run a 28% overdrive and some times when we are touring and fully loaded and in the mountains it would be nice to have a gear between 2nd and 3rd? My calculations show that at 30mph 2nd is 3600rpm(manual figures) but in overdrive(28%) it would be 2800rpm Now I have had a good look at the top cover and operating lever and I think I can drill a hole at about 28degs and to the side and in front of the 3rd & 4th one then weld a boss on I could have a switch that would give o/d in 2nd. I have ordered a reversing light switch and a NOS Lucas o/drive switch The reversing light would be the easiest to fit but I do not think it is sealed against oil getting into the switch. Now you can tell me I am completely bonkers(but then we already know that!) Roger ps 1st photo scroll type and later seal type(Triumph) others new on left I fitted a small seal to maintain strength Link to comment Share on other sites More sharing options...
oldtuckunder Posted January 31, 2019 Share Posted January 31, 2019 16 minutes ago, rogerguzzi said: Now I have had a good look at the top cover and operating lever and I think I can drill a hole at about 28degs and to the side and in front of the 3rd & 4th one then weld a boss on I could have a switch that would give o/d in 2nd. Dumb idea, but rather than fitting switches to allow overdrive in 2nd, 3rd, 4th would it be easier to rig something that disallowed it in 1st and Reverse? Alan Link to comment Share on other sites More sharing options...
JohnD Posted January 31, 2019 Share Posted January 31, 2019 A logic problem, Alan, that I think you'll work out has the same solution, either way! John Link to comment Share on other sites More sharing options...
Nick Jones Posted January 31, 2019 Share Posted January 31, 2019 So what is the rpm at 30mph? Are you not just creating another third gear, albeit an electrically actuated one? If it is at a useful interval, go for it! Alan’s suggestion definitely worth considering though too long since I’ve been into a single rail to make any useful suggest beyond that. Reverse already has a switch of course so just first to worry about. Link to comment Share on other sites More sharing options...
mpbarrett Posted January 31, 2019 Share Posted January 31, 2019 is the OD ok for the torque? I know the OD on the TR6 had overdrive (D type?) on 2, 3 and 4th gear so I guess a 4 cylinder would be ok. Wonder why it wasn't done before? Easy way is to make a bracket for a first gear switch and a relay driven from the reverse switch that inhibits OD when in reverse. I made my own bracket for a couple of micro switches for 3rd and 4th gear (as I didn't have the original switches or brackets), so that if you change from 3 to 4 in OD it drops the OD out so you go 3, 3OD, 4, 4OD instead of staying in OD in-between 3OD and 4OD. Only problem with this is that 3OD and 4 is I think almost the same ratio!! mike Link to comment Share on other sites More sharing options...
Nick Jones Posted January 31, 2019 Share Posted January 31, 2019 A-type OD on the TRs is the one considered manly enough to be used in second. Can’t remember about J-type but possibly not. Should be ok for a 1500 4 pot though. Might be some benefit to raising the operating pressure to increase the clutch clamping force. This is the main difference between J-types used on bigger engined cars. Increased parasitic losses is the downside. Link to comment Share on other sites More sharing options...
rogerguzzi Posted January 31, 2019 Author Share Posted January 31, 2019 Hello Nick 30 mph = 2nd 3600 2nd o/d 2800(28%) 3rd 2315 so yes a 7 speed gearbox! (the TR people rave about a 7 speed gearbox?) I think if a J type can take a TR6 at 150? bhp in 3rd it should cope with 90 to 100 bhp max(I hope from my new engine!) Plus (here we go again?) of grinding a gap in the overdrive operating arm so it drops out between 3rd and 4th gears(same as the big boxes) so my home built(simple logic box will drop the o/d out) Roger ps double daft now? Link to comment Share on other sites More sharing options...
rogerguzzi Posted January 31, 2019 Author Share Posted January 31, 2019 Hello Mike I think you may be talking of a 3 rail gearbox? Its all inside on a single rail! Roger ps there is the remote bit but I do not think there is enough room or accuracy to fit a switch here but I will look Link to comment Share on other sites More sharing options...
toofast2race Posted February 1, 2019 Share Posted February 1, 2019 J Types don't like engaging at low propshaft rpm - they slip on engagement. Must be a pressure thing. A types always have the pressure ready to slam the OD clutch in whereas the J Type the pressure has to build once the solenoid is flipped. At least that's my understanding. My 2100 has J overdrive on 2nd but its next to useless unless engaging at 6500rpm - it has usually kicked in by the time I'm on the rev limiter at 7200. I assume that playing with the pump setting and spring pressures in the overdrive and new linings would help/solve these issues. When I got a rebuilt comp spec overdrive from Rugby overdrive spares http://www.odspares.com/ they reckoned with modified settings and better material clutches that they now fit as standard, you could use overdrive in all forward gears. Link to comment Share on other sites More sharing options...
SDerbyshire Posted February 1, 2019 Share Posted February 1, 2019 7 hours ago, toofast2race said: J Types don't like engaging at low propshaft rpm - they slip on engagement. Must be a pressure thing. A types always have the pressure ready to slam the OD clutch in whereas the J Type the pressure has to build once the solenoid is flipped. At least that's my understanding. My 2100 has J overdrive on 2nd but its next to useless unless engaging at 6500rpm - it has usually kicked in by the time I'm on the rev limiter at 7200. I assume that playing with the pump setting and spring pressures in the overdrive and new linings would help/solve these issues. When I got a rebuilt comp spec overdrive from Rugby overdrive spares http://www.odspares.com/ they reckoned with modified settings and better material clutches that they now fit as standard, you could use overdrive in all forward gears. Thanks for this informtion, my j type overdrive is less willing to engage in 3rd than 4th, guess this is why! steve Link to comment Share on other sites More sharing options...
mpbarrett Posted February 1, 2019 Share Posted February 1, 2019 (edited) 9 hours ago, rogerguzzi said: Hello Mike I think you may be talking of a 3 rail gearbox? Its all inside on a single rail! Roger ps there is the remote bit but I do not think there is enough room or accuracy to fit a switch here but I will look yes sorry mine is 3 rail and everything is on the outside if room is tight you could always use an electronic magnetic proximity detector, usually short range but can be very small. Use that to drive a relay with another relay driven from reverse to ensure you don't engage reverse and OD. As others have said the problem might be lack of pressure from the oil pump as the speed will be low. Cant remember what it was like on my TR6 don't think I used OD on second very often.... mike Edited February 1, 2019 by mpbarrett Link to comment Share on other sites More sharing options...
Nick Jones Posted February 1, 2019 Share Posted February 1, 2019 8 hours ago, toofast2race said: J Types don't like engaging at low propshaft rpm - they slip on engagement. Yes. Good point! Another key difference between A and J is that the A pump is in circuit all the time and maintaining pressure against an accumulator so will always engage but can sometimes drop out again at really load speed. J-type only pump pressure when engaged to reduce parasitic losses. Seem to remember reading somewhere (Dolly 1500 WSM maybe) that the OD should engage at speeds over 30 mph in third. The one in my Herald used to do a bit better and kick in at around 22 mph in 3rd. Down to the condition of the pump itself I guess. Spitty could be a bit worse due to the higher 3.63 gearing giving lower mainshaft speeds and thus lower pumping rate for a given road speed. Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 1, 2019 Author Share Posted February 1, 2019 Hello All Thank's for all your input and I was going to forget the idea but after a bit more research I found a question had been asked on the TRR forum. Most of the people say it works ok but a lot do not need it with the TR6 but others say it is great and works ok? The second gear ratio is a touch taller than Spitty and the diff is taller as well so if it works on a TR6? Spitty's gearbox output shaft would be going a bit quicker? So seeing I have ordered the switches its game on again? and its worth a try(and it keeps my old brain going!) Plus I still fancy a 7 speed gearbox (boys and toys?) some comments I did this about 8 years ago. The overdrive is still as original, and I use it all the time. I am aware that it is considered unsuitable, so only rarely engage while under heavy acceleration. My engine produces circa 180bhp. The only overdrive issues I have had are those bloody awful aftermarket micro-switches, with terminals made of re-cycled dog poo! They snap off if you look at them sideways. Get secondhand Lucas versions from TRshop. Make sure the operating height is correct. Follow wiring as in CP. In my opinion, it's a good mod I did mine about 20 years ago with no issues so far, its very useful around town and in traffic but I rarely use it when driving hard I have a Stag gearbox with a 28% J type OD, built for me by Pete Cox, who also modified it to work in 2nd gear ( as already stated, it's as simple as using an A type top cover with the extra switch ) and I have to say it's really made a difference ( it's in a TR4 ) - fitting was a bit of a pain but perfectly do-able. I don't thrash it if I'm using 2nd OD but as suggested by several others, it makes driving in towns or slow speed areas more pleasureable, with far fewer gearchanges if you don't want to - cruising is also far more relaxed. Roger Link to comment Share on other sites More sharing options...
Nick Jones Posted February 1, 2019 Share Posted February 1, 2019 Crack on. Watching with interest. Just suggest making sure the OD pump is as good as it can be so it works as well as it can at low speeds. Link to comment Share on other sites More sharing options...
toofast2race Posted February 2, 2019 Share Posted February 2, 2019 Somewhere in the historic archives , Special Tuning - Dolonite Sprint BL Abingdon homologation papers there is a explanation on how to uprate the J type OD pressures. My mates at Markich Triumph have an original copy ( for Bathurst wannabes?!) - I’ll try to copy it Link to comment Share on other sites More sharing options...
Nick Jones Posted February 2, 2019 Share Posted February 2, 2019 Understand that they run different pressures for different applications anyway. More engine torque, more pressure. There is also a mod that changes the rate of engagement - makes ‘em somewhat abrupt for road use. Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 2, 2019 Author Share Posted February 2, 2019 Hello All Yes I know they use different pressures for bigger/heavier cars When I built mine last time (5 years ago) I bench tested it with an electric motor as Buckley suggests and it was right for a spitfire. Will be at stoneleigh next Sunday I will ask the o/d people about pressures and perhaps buy a stronger spring etc Just received the switches this morning and the o/d one is proper Lucas dated 1996 and only about £6 free p&p Roger Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 2, 2019 Author Share Posted February 2, 2019 Hello All A bit of progress and a C**k up! The new Lucas switch I bought has a much bigger thread!!!! I have drilled and threaded the top cover to take a reversing light switch and ground a small radius on the lever and it works. My only concern is it is not sealed against oil like the o/d ones and the stem is thinner! So I may look at making a boss to be welded on and incorporate a larger plunger inside and perhaps buy another o/d switch or thread it to suit the bigger one Still its looking do able? Roger Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 4, 2019 Author Share Posted February 4, 2019 Hello All I decided to get a boss welded onto the top cover so that's with a mates son who is the dogs doo dah's at welding. I had a look at the Moss catalogue and the 4 springs are the same in a TR6 as Spitty so I do not think it will slip in direct drive ever? I found this information on pressures. Triumphs Only, Inc. - Triumph Technical Service Bulletin "J" Type Overdrive Unit- All Models April, 1973 A new "J" Type Overdrive Unit is currently being incorporated on the Triumph range of vehicles; consequently, the "A" and "D" Types will be discontinued. Incorporation of the "J" Type Unit was effective commencing with the following vehicle identification numbers: Model Vehicle Ident. # Color Number Part # Working Pressure Stag LE 20857 Yellow 115837 312377 510-540 TR-6 CF 1 Blue 115838 313242 430-460 Spitfire * Lilac 115840 313305 320-350 GT-6 * Lt. Green 115850 313304 350-380 * - Estimated incorporation -- Late February, 1973 Hydraulic Pressure Test When running in direct drive, a residual pressure of 20 lbs. per square inch maintains the overdrive unit in a primed condition and provides lubrication. When overdrive is selected, the hydraulic pressure is increased to within the figures quoted above, To check the operating pressures: 1. Check that the gearbox oil level is correct. 2. Remove the hexagon headed plug adjacent to the solenoid and fit hydraulic pressure gauge L188A together with the adaptor L188A-2. 3. Jack up the rear wheels and run the transmission at approximately 25 m.p.h. Note 1. When in direct drive the residual pressure reading should be approximately 20 lb./in. Note 2. When the overdrive is engaged, the pressure should be as specified. Interchageability Of Parts "J" Type Overdrive parts are not interchangeable with those for "A" or "D" Type Units. Roger Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 5, 2019 Author Share Posted February 5, 2019 Hello All Been thinking again(dangerous?) If Triumph say test at 25 mph on a TR6 that would be about 1150 rpm in 4th so my guess is that they expected those pressures at 1000 rpm on the gearbox output shaft? (22mph) Or 2100 rpm in 2nd Which on Spitty 1000 rpm would be about 18 mph in 4th So 18 mph in 2nd is about 2150 rpm or about 1700 rpm in O/D 2500rpm = 21.5mph 2nd & 27.5mph 2nd O/D So with a bit of luck it will prove a useful gear at times. Roger Link to comment Share on other sites More sharing options...
IainR Posted February 6, 2019 Share Posted February 6, 2019 TBH I have OD 2nd on my 6 and have never really found a use for it on the road. But, I do find OD 2nd very useful on the short straight between the Hairpin and Barn at Cadwell. Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 6, 2019 Author Share Posted February 6, 2019 47 minutes ago, IainR said: TBH I have OD 2nd on my 6 and have never really found a use for it on the road. But, I do find OD 2nd very useful on the short straight between the Hairpin and Barn at Cadwell. Hello Ian I can see that it may not be useful on a TR6 but on Spotty I sometimes find the jump between 2 nd and 3 rd a bit much when we are fully loaded and on mountain passes its either rev the nuts off or bog down if not careful. The mod is half done now so worth a try (plus I love tinkering?) Roger I can see it may be not much use on a TR6 but on Spitty I some times find the jump between 2nd I can see on a TR6 it may be not worth it but on Spitty the jump between 2nd and 3rd Link to comment Share on other sites More sharing options...
IainR Posted February 7, 2019 Share Posted February 7, 2019 It may well be Roger, and at the very least you can join in the I have a seven speed box conversations whilst leaning on the bar. I know that on my mk3 spit with standard OD then OD 3rd was the ratio of choice in traffic for much the same reasons you quote for the OD 2nd option. I never explored the 2nd gear option in those days and spitty has now long gone to the great Triumph dealer in the sky. Link to comment Share on other sites More sharing options...
rogerguzzi Posted February 7, 2019 Author Share Posted February 7, 2019 Hello Ian The thought had not crossed my mind !!!!!!!!! I might even say 8 and not mention one is reverse! Roger ps I have modified a coupling so I can drive the input shaft at 1425 rpm direct from a 1/2 horse motor which I think is just about right it should give 26 mph in 4th and 19mph in 3rd but only 12.5 mph in 2nd! But if it works in 3rd that would be ok as 18 to 20 mph in 2nd would give the 1000 rpm needed I think? Link to comment Share on other sites More sharing options...
IainR Posted February 8, 2019 Share Posted February 8, 2019 22 hours ago, rogerguzzi said: The thought had not crossed my mind !!!!!!!!! Link to comment Share on other sites More sharing options...
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