classic225 Posted October 11, 2013 Report Share Posted October 11, 2013 Hi, As my 3A and 4 have non overdrive boxes,I was always on the lookout for overdrive gearboxes.I now found two overdrive boxes from TR2's. Would a 2 overdrive box fit in the 3A and/or would the overdrive bolt on(after changing the outgoing shaft)the 4 gearbox,so I wouldn't loose the 1st syncro gear. Thanks Quote Link to post Share on other sites
EdwinTiben Posted October 11, 2013 Report Share Posted October 11, 2013 Hi ! It would fit as a swap i believe, take a look at http://www.tr3a.info/gearbox_swap.htm I was advised to use the tr4 overdrive because it has bigger pistons in comparison to the tr2 OD. Quote Link to post Share on other sites
vivdownunder Posted October 11, 2013 Report Share Posted October 11, 2013 Firstly check the Overdrives. Early TR2 units with ID plate 22/61275 were weaker and only suitable for use on top gear (not the TV show!). Later TR2's had the stronger O/D 22/61374 that operated on 2nd, 3rd and top. 3 synchro gearboxes after TS26825 are longer lasting than TR2 gearboxes. a needle roller bearing replaced the plain bush on the mainshaft. If fitting a 3 synchro O/D to a 4 synchro box, the adaptor plate can be different. You'll need to instal supplementary O/D looms, relays and engagement switches. That's a toggle switch on the dash for the 3A and an additional RHS lever switch on the TR4. Viv Quote Link to post Share on other sites
BlueTR3A-5EKT Posted October 11, 2013 Report Share Posted October 11, 2013 Hi, As my 3A and 4 have non overdrive boxes,I was always on the lookout for overdrive gearboxes.I now found two overdrive boxes from TR2's. Would a 2 overdrive box fit in the 3A and/or would the overdrive bolt on(after changing the outgoing shaft)the 4 gearbox,so I wouldn't loose the 1st syncro gear. Thanks As stated the TR2 original overdrive was only man enough for engagement in 4th gear. See the reference numbers given in this thread. Yes the TR2 overdrive gearbox as an assembly will slot into your TR3A. All you need to do is add wiring. Yes you could bolt the overdrive to the back of your existing 3 synchro non overdrive gearbox but only once you had swapped the mainshaft from the overdrive gearbox and the overdrive mounting plate. The overdrive mainshaft from the TR2 gearbox which is 3 synchro will not fit a 4 synchro gearbox assy. See the Moss catalogue for part number changes. 3 synchro http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=2002 4 synchro http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=2003 The same overdrive adaptor plate fits all TR gearboxes TR2-6 when the A type overdrive is used. Cheers Peter W Quote Link to post Share on other sites
classic225 Posted October 11, 2013 Author Report Share Posted October 11, 2013 Thanks guys,great info! The reason I would go for a TR2 box is that it's the only one I can get my hands on for now. TR3 and 4 overdrive are not cheap,and difficult to find for a "normal" price. I can buy two TR2's and they both have overdrive's,seems a bit of a waste to part the cars out but I want an overdrive pretty bad in my cars. Yves Quote Link to post Share on other sites
BrianC Posted October 12, 2013 Report Share Posted October 12, 2013 The early overdrives can be upgraded to operate on 3rd and 4th by replacing the clutch operating pistons with the later, larger diameter ones. [see TR2-3A Workshop Manual]. Of course you also have to replace or modify the top cover to incorporate the additional isolator switch. Probably woth checking with a specialist such as Overdrive Repair Services (ORS) in Sheffield for parts/prices and labour for a reliable job. Quote Link to post Share on other sites
classic225 Posted October 12, 2013 Author Report Share Posted October 12, 2013 Thanks Brian, Great info. Yves Quote Link to post Share on other sites
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